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Metabolic activity pattern in the motor and somatosensory cortex of monkeys performing a visually guided reaching task with one forelimb
~ ) Pergamon
0306-4522(95)00516-1
Neuroscience Vol. 72, No. 2, pp. 325 333, 1996 Elsevier ScienceLtd Copyright © 1996 IBRO Printed in Great Britain. All rights reserved 0306-4522/96 $15.00 + 0.00
M E T A B O L I C A C T I V I T Y P A T T E R N IN THE M O T O R A N D S O M A T O S E N S O R Y C O R T E X OF M O N K E Y S P E R F O R M I N G A V I S U A L L Y G U I D E D R E A C H I N G T A S K WITH ONE FORELIMB* Y. D A L E Z I O S , V. C. R A O S and H. E. S A V A K I t Laboratory of Functional Brain Imaging, Department of Basic Sciences, Division of Medicine, School of Health Sciences, University of Crete, P.O. Box 1393, GR-71110 Iraklion, Crete, Greece A~traet--The [~4C]deoxyglucose method was used to map the metabolic activity in the primary somatosensory and motor cortex in monkeys (Macaca nernestrina) performing a unimanual task. The task required visually guided reaching and target holding at a rate of about 10 movements per min. The entire dorsoventral extent of the cortical region lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulci was. reconstructed on the sagittal plane, from horizontal sections aligned on the fundus of the central sulcus. The metabolic mapping of the control monkey demonstrated homogeneous activity all around the central sulcus, bilaterally. The mapped activity in the performing monkeys displayed two different patterns. The first pattern, contralateral to the moving forelimb, was characterized by several discrete regions of increased metabolic activity, which were symmetrically distributed in a mirror image fashion around the fundus of the central sulcus. These activated regions correspond to the lower body, forelimb, and mouth areas of representation of body parts in previously reported maps in primary motor and somatosensory cortical areas. The second activity pattern ipsilateral to the moving forelimb, displayed activated somatosensory and motor regions corresponding only to the lower body, and mouth representations. Our study provides a continuous, high resolution map of activity pattern in the entire primary motor and somatosensory cortices, which demonstrates that the reaching forelimb is controlled by a discrete subregion in the contralateral somatosensorimotor cortex, whereas other subregions of body representation are actively involved, bilaterally, during the performance of a relatively simple motor behaviour. Key words: primary motor cortex, primary somatosensory cortex, central sulcus, reaching movements, [J4C]deoxyglucose.
Ipsilateral corticospinal fibres, originating from the trunk and proximal limb areas of the m o t o r cortex 5,25,26,2s'3s have been considered responsible for mediating control over the ipsilateral f o r e l i m b : '25 The long standing paradox of a split-brain monkey reaching accurately to a visual target with the forelimb contralateral to its "blind" hemisphere 7'29 has been explained by the implication of this descending corticospinal pathway. It has been proposed that control of the reaching forelimb in the split-brain monkey is shifted from the visually deafferented contralateral hemisphere to the visually intact ipsilateral o n e : The 2-[14C]deoxyglucose ([14C]DG) method applied on intact and split-brain monkeys performing a unimanual reaching task after visual pattern discrimination, revealed activation of the somatosensorimotor cortex in the hemisphere contralateral to the moving
forelimb, irrespective of whether this hemisphere was intact or visually deafferented. 32 Thus, in contrast to Brinkman and Kuypers' proposal, 4 it was recently suggested that visually guided reaching with the forelimb contralateral to a "blind" hemisphere is subserved by that hemisphere's somatosensorimotor cortex and not by the cortex of the ipsilateral "seeing" hemisphere. 3z The objective of the present study was to further examine the underlying mechanisms of reaching, by providing a detailed, quantitative, bilateral, pictorial view of the metabolic pattern of activity within the entire precentral primary m o t o r (MI) and postcentral primary somatosensory (SI) cortex in monkeys performing a unimanual, visually guided, arm reaching and key pressing task. This allows us to avoid averaging glucose utilization rates within relatively wide M I subregions, and to obtain measures of metabolic activity within the specific m o t o r areas of body representation (i.e. mouth, hand, arm, lower body). To this end, the distribution of the [14C]DG labelling in the cortex around the central sulcusof each hemisphere in horizontal autoradiographic brain sections (three adjacent 20-/~m-thick sections
*Part of this work was presented at the 19th annual meeting of the European Neuroscience Association. tTo whom correspondence should be addressed. Abbreviations: [14C]DG, [14C]deoxyglucose; LCGU, local cerebral glucose utilization; L/R % DIF, left to right hemispheric differences; MI, primary motor cortex; SI, primary somatosensory cortex. 325
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every 140/~m) of control and reaching monkeys was r e c o n s t r u c t e d in t w o d i m e n s i o n s , o n t h e s a g i t t a l plane.
EXPERIMENTAL PROCEDURES
Subjects Three adult female Macaca nemestrina monkeys weighing between 3.5 and 4.0 kg were used. The first monkey was trained to perform the visually guided reaching task with its right forelimb. The second monkey was trained to perform the same task with its left forelimb. The third monkey was an untrained normal control, seating in front of the nonfunctioning test panel and receiving neither visual stimuli nor liquid reward during the [14C]DG experiment. All three monkeys had their head fixed, while a water delivery tube was positioned close to the m o u t h of the two performing animals. Task and apparatus The test panel in front of the monkey contained two push-buttons which could be illuminated from behind. They were spaced 8.7 cm from each other and arranged in a line 45 ° distal to the frontal plane, in 3-D space. The central, start-button was located in the midsagittal plane (0 °) at shoulder height and 25 cm from the monkey, whereas the peripheral, target-button was located 45 ° to the right or to the left, for the monkey reaching with the right or the left forelimb, respectively. The intertrial intervals ranged between 1 and 1.5 s. The monkey was required to press and hold the illuminated central button for 1.5 2.5 s, until this was turned off and the peripheral button was lit up. Within the specified upper limit of reaction and movement time (1.35 s) the monkey was required to release the central and press the peripheral button. After holding the peripheral button for 1-1.5 s, a liquid reward was delivered. The two trained monkeys reached a performance criterion of > 90% correct responses, resulting in 8 12 single-directional movements per min during the 45 min of the [14C]DG experimental period. Measurement o f glucose utilization On the experimental day, monkeys were subjected to femoral vein and artery catheterization under ketamine hydrochloride anaesthesia (20 mg/kg, i.m.). The monkeys were allowed 4-5 h to recover from anaesthesia. The procedure used for determining the local cerebral glucose utilization ( L C G U ) was the same as that previously described. 32 The measurement of L C G U was initiated by the intravenous injection o f [t4C]DG as a pulse of 100 # Ci/kg of, 2-deoxy-D-[1-14C]glucose (specific activity 50-55 mCi/mmol, NEN) dissolved in physiological saline. Timed arterial samples were collected from the catheterized femoral artery during the succeeding 45 min at a predetermined schedule. Plasma [~4C]DG concentrations were determined by liquid scintillation spectrometry, and plasma glucose concentrations were measured with a Beckman Glucose Analyser. At 45 min after the [14C]DG administration, the animal was killed by intravenous injections of 50 m g o f sodium thiopental in 5 ml saline, and then a saturated potassium chloride solution to stop the heart. The brain was removed, frozen in Freon at - 5 0 ° C , and stored at - 7 0 ° C until sectioned for autoradiography. Three 20-/~m thick adjacent horizontal sections of brain were cut every 1 4 0 # m in a cryostat at - 2 0 ° C , and autoradiographs were prepared by exposing these sections (together with precalibrated [~4C]standards) with medical X-ray film (Kodak OM1) in X-ray cassettes. The intermediate sections, which were not cut for autoradiography, were used for histologic staining. Quantitative densitometric analysis of autoradiographs was carried out with a computerized image-processing system (Imaging Research Inc., Ontario, Canada), which
allowed integration of the L C G U values over the entire extent of each area of interest. L C G U was calculated from the kinetic constants for the monkey, 23 by the operational equation of the [t4C]DG method. 37 Normalization of the L C G U values was based on the average white matter value pooled across all three monkeys (16/~mol/100g/min). Left to right hemispheric differences (L/R % D I F ) were calculated, and analysed by the paired t-test, as previously described. 32 In a similar way, per cent activation in each region (i) within each hemisphere in the active (A) monkeys was calculated in comparison to the value of the homologous cortical area in the control inactive (C) monkey, by the equation: %Ci = ( A i ~ i)/C i * 100. Two dimensional reconstruction A two dimensional reconstruction of the metabolic activity pattern within the entire dorsoventral extent of the cortical area lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulci in each hemisphere was generated on the sagittal plane. The distribution of activity in the anteroposterior extent in each horizontal section was determined by measuring L C G U values pixel by pixel (resolution, 35 50 ~tm/pixel) along a line parallel to the surface of the cortex approximately midway through its depth (covering cortical layers I I V , see Fig. 1B, DR). The data arrays resulting from anteroposterior image segmentation in adjacent horizontal sections were aligned around the fundus of the central sulcus. The plotting resolution of both anteroposterior and dorsoventral dimensions was 100~m. Occasional missing data arrays in the dorsoventral dimension were filled using linear interpolation between neighbouring values. The m a p of hemispheric differences was obtained by computer generated subtraction of the digitized ipsilateral metabolic m a p from the one contralateral to the moving arm, after alignment of the two maps around the fundus of the central sulcus. The activated regions in the precentral and the postcentral banks in our m a p s were compared to previously reported MI and SI maps of body representation. Specifically, the lower body-hindlimb (b) representation in the MI m a p of Fig. 23 published by Woolsey 43 covers 27% (3.7 cm) of the total mediolateral extent of the precentral bank (13.5 cm). The shoulder-arm (a) representation covers 18% (2.4 cm), the hand-digits (h) area 21% (2.8 cm), and the m o u t h (m) area 34% (4.6 cm) in the same map. For reasons of comparison, in Fig. 1A (Rc), the borders of the respective relative extents in our maps are marked on the bottom abscissa which represents the dorsoventral extent of the central sulcus. These markings should be considered as only indicative borders, not only because of the way they were estimated, but also because of the known overlaps between cortical motor areas controlling distinct body parts. The relative extent of the same areas in the postcentral bank were similarly estimated to be, b = 32%, a = 22%, h = 24%, and m = 22% in SI-3b m a p of Fig. 1 published by K a a s ' group. 3~ In Fig. IA (Rc), the respective relative extents in our m a p s are labelled on the top abscissa. Unfortunately, histologic staining of the frozen sections from the nonperfused brains in our study, did not allow for discrimination of cytoarchitectural borders. Thus, the boundaries between areas 3a, 3b, 1, and 2 indicated in Fig. 1A (Rc) were calculated according to those reported earlier (Figs 3 and 8 of Juliano et al.2t). These labellings should also be considered as only indicative borders. RESULTS Both monkeys performing visually guided reaching m o v e m e n t s d u r i n g t h e [14C]DG e x p e r i m e n t d i s p l a y e d m e t a b o l i c a c t i v a t i o n in M I ( a r e a 4) a n d SI ( a r e a s 3, a n d 1-2) b i l a t e r a l to t h e m o v i n g f o r e l i m b w h e n c o m p a r e d w i t h t h e c o n t r o l m o n k e y (see % C in
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Table 1). Smaller, bilateral, metabolic activation was measured in the transition of premotor area 6 to primary motor area 4, lying between the posterior crown of the arcuate and the anterior crown of the central sulcus. Paired t-test statistics revealed that the metabolic activation within MI and SI in the hemisphere contralateral to the moving forelimb was always significantly higher than that in the ipsilateral homologous cortical area (see L/R and R/L%DIF in Table 1). In contrast, there was no consistently significant side to side difference within the region of transition of area 6 to area 4. In summary, the quantitative estimation of average glucose utilization value within the entire extent of MI and SI demonstrated that moving one forelimb to a visual target activates the primary motor and somatosensory cortices bilaterally, although the contralateral side is significantly more activated than the ipsilateral one. The question remained, which areas of body representation in MI and SI reflect the measured activation? Is it, simply, the forelimb area of representation which is bilaterally activated displaying higher contra- than ipsilateral values, or the distribution of metabolic activation within the different areas of representation is more complex? We attempted to answer this question by the two dimensional (2-D) reconstruction of metabolic maps of the cortex around the central sulcus. The 2-D reconstructed metabolic maps exhibit different global spatiointensive patterns depending on (i) the performance on the task, and (ii) the side of the hemisphere relative to the moving forelimb. The reconstructed maps of the cortex around the central sulcus in the left and right hemispheres (L and R) of the inactive control monkey (c) are both rather homogeneous (Fig. IA: Lc and Rc). The metabolic activity in the two unimanually performing monkeys display two different patterns. The first activity pattern, which is observed contralateral to the moving forelimb in both active monkeys, displays a fish-bone shape around the fundus of the central sulcus. In other words, this pattern is characterized by several discrete regions of increased metabolic activity, which are symmetrically distributed as mirror images around the fundus of the central sulcus, and which extend in the precentral and postcentral banks as well as beyond the anterior and posterior crowns of the sulcus (Figs 1A and 1B: CONTRA). In general, the metabolic activations in the precentral bank which correspond to MI regions are lower than those in the postcentral mirror image areas which correspond to SI regions. The symmetric activation pattern around the fundus of the central sulcus refers to a symmetry around the approximate MI-SI border, which is similar to that illustrated in Woolsey's homuncular representation. Comparison of our metabolic maps with previously reported MI and SI somatotopic maps revealed that the activated regions in the somatosensorimotor cortex contralaterai to the moving forelimb cover all body part representations, i.e. the
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lower body-hindlimb (b), the arm-shoulder (a), the hand-digits (h), and the mouth (m) areas (see Fig. 1A: Rc for indicative dorsoventral levels of body part representations). The second activity pattern, which is observed ipsilateral to the moving forelimb in both active monkeys, displays precentral MI and postcentral SI regions, which are activated symmetrically around the fundus and correspond mainly to the lower body-hindlimb and mouth areas (Figs 1A and I B: IPSI). In summary, during a simple, liquid rewarded, unimanual, visuomotor task, (i) the forelimb representation within the MI and SI is activated only in the hemisphere contralateral to the moving arm, whereas (ii) the lower body and the mouth representations are activated within the MI and SI in both hemispheres. Area 3a, which is located around the depth of the fundus, is more active in both hemispheres in the monkey moving the left than in the monkey moving the right forelimb. However, the maps of hemispheric differences in the two reaching monkeys are similar, demonstrating specific activation only within the forelimb area in both MI and SI (Figs 1A and IB: CONTRA-IPSI). Four metabolic bands parallel to the posterior crown of the central sulcus are observed in the activated SI-forelimb area, with a peak to peak distance varying between 2 and 5 mm. Some of these bands extend beyond the posterior crown, within the SI area 2. Computer generated magnification of the activated MI-forelimb region, reconstructed at a higher resolution (28#m/pixel), displayed bands symmetric to the SI-forelimb ones as to the axis (fundus) of the central sulcus, and parallel to the anterior crown (Fig. 2). The region of cortical transition of area 6 to area 4 in both hemispheres of both performing monkeys is more active and labelled in a less uniform manner than the homologous region in the control monkey. Although the effect within the transition of area 6 to area 4 appears to be mostly bilateral, a region which is specifically activated in the hemisphere contralateral to the moving forelimb is differentiated in the map of hemispheric differences in both reaching monkeys. This region is located caudal to the posterior crown of the arcuate sulcus and at the same dorsoventral level with the MI-forelimb area (Figs 1A and 1B: CONTRA-IPSI).
DISCUSSION
The present study is the first to provide a quantitative, bilateral, pictorial view of the metabolic pattern of activity within the cerebral neocortex around the central sulcus (cortex lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulcus) in monkeys performing a visually guided reaching task with one forelimb. The observed symmetry between the MI and SI patterns of activity as to the fundus of the central sulcus is in
accordance with the overall macroscopic somatotopic pattern in Woolsey's homuncular representations in MI and SI. 43 Comparison of our data with existing functional maps of the body representation around the central sulcus 3~'43 demonstrates for the first time that the areas corresponding to the lower body and the mouth representations are activated in the MI. Thus, the present results verify the motor control of a reaching forelimb by the contralateral rather than the ipsilateral hemisphere, in contrast to a previous proposal based on the anatomic projections from MI to ventral horn cells innervating the proximal musculature of the ipsilateral limb, 4 and in accordance with our recent suggestion. 32 Within the area of SI-forelimb representation contralateral to the moving forelimb, "the activated patches observed in the individual horizontal autoradiographic sections formed active bands in the reconstructed metabolic map. L C G U metabolic studies of the visual, auditory, and somatosensory cortex have demonstrated labelling patterns consisting of "columns" or "strips". ~'~3"2~The active "strips" in SI are reported to vary with the stimulus location and the field size on the skin. 2~ Discrete forelimb skin stimuli were reported to evoke elongated active [14C]DG "modules" within an extensive region of SI, with a peak to peak distance 2-6mm. 4° This is consistent with the distance between two adjacent metabolically active bands in the SI-forelimb representation in our study. Observed bands in our study may be related to the reported cortical inpuwoutput clusters associated with callosal, associational, and thalamocortical projections. 17"~9'2° However, the reported gradient of callosal projections, with area 3b displaying few, area 1 intermediate, and area 2 dense connections, 24 is the inverse of the intensity of metabolic activity observed in our map. Also, the distribution and density of the association connections within areas 3b, 1, and 2 ~8"4~do not correspond to the LCGU spatiointensive pattern observed in this study. The pattern we observed is more consistent with the thalamocortical projection system, which is heavy in areas 3a, 3b, and less dense in areas 1, 2. 30.36 The observed metabolic fractionation of the SI-forelimb area into elongated units may reflect the continuous representation of each activated forelimb segment across the distinct maps in SI subregions. 3j Our finding that, more active bands are located between the fundus and the posterior crown of the central sulcus (area 3), fewer ones are located around the crown (area 1), and there is a lack of discretely activated bands caudal to this crown (area 2), is compatible with the reported discrete representation in area 3, ~5 wide field representation in area 1, ~6 and extensively overlapping representation in area 2 where multiple functions apart from body parts are represented. 14 Within the area of MI-forelimb representation, although no activated patches were apparent by visual inspection of the individual horizontal
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Fig. 1. Two dimensional reconstruction of the LCGU values (in/~mol/100 g/min) in the cortical region lying between the posterior crown of the arcuate (lower border) and the anterior crown of the intraparietal sulcus (upper border of reconstructed images). Solid line at zero anteroposteriority represents the fundus of the central sulcus, which was used as the landmark for alignment of adjacent horizontal sections. Dotted lines represent the anterior (lower) and the posterior (upper) crowns of the central sulcus. (A) CONTRA and IPSI, left and right hemispheres, respectively, in the monkey reaching with the right forelimb. CONTRA-IPSI, map generated after subtraction of the reconstructed ipsilateral central sulcus from the one contralateral to the moving forelimb. Lc and Rc, left and right hemispheres in the control inactive monkey. Approximate boundaries of body part representations in the precentral MI and postcentral SI cortical areas are labelled in the bottom and top abscissae of Rc map, respectively: a, arm-shoulder; b, body-hindlimb; h, hand-digits; m, mouth. Indicative borders between areas 3a, 3b, 1, and 2 are marked at the level of the forelimb representation in SI. LCGU, scale of local cerebral glucose utilization values in all reconstructed maps but the one representing the interhemispheric differences. LCGU Dif, scale of values in the maps representing the interhemispheric differences. (B) IPSI and CONTRA, left and right hemispheres, respectively, in the monkey reaching with the left forelimb. CONTRA-IPSI, as in case A above. DR, diagrammatic representation of the anteroposterior extent of the reconstructed cortical area (dashed line) in horizontal sections at 10 dorsoventral levels spaced about 2 mm apart. A, anterior; AS, arcuate sulcus; CS, central sulcus; D, dorsal; I, intraparietal sulcus; P, posterior; V, ventral.
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autoradiographic sections, a metabolically active region was observed in the caudal zone of the precentral bank contralateral to the moving forelimb within the reconstructed metabolic maps. This finding is compatible with the suggestion that neurons in caudal MI contribute to proprioceptive and cutaneous guidance of ongoing movements. 12 The bands seen within the activated MI-forelimb region at a
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higher resolution, were not arranged in a concentric "ringlike''42 or "horseshoelike ''34 pattern, and did not span both areas 4 and 6. 34,42Instead, these bands were parallel to each other, and displayed an anteroposterior periodicity falling within the range of dimensions of both the somatosensory input and motor output clusters reported in M I . 2'3'27 However, given that (i) the anterior, and posterior ventrolateral, as well as the ventromedial thalamic neurons, which mediate input from the globus pallidus, the cerebellum, and the substantia nigra, respectively, converge on single cortical modules in MI, 6 (ii) the projection of the supplementary and cingulate motor areas to the forelimb region of MI has no precise topographical organisation,39 and (iii) several intrinsic connections exist inside the MI, 39 the activated bands in our study may not reflect somatotopic representation based on input and output. Alternatively, these bands may represent the spatial organization of motor cortical neurons encoding specific kinematic or dynamic parameters of reaching movements.8'9'22'33The bilaterally activated band we observed in the ventral part of MI-forelimb area in the reaching monkeys, complements the neurophysiologic finding that a specialized efferent zone exists between the face and digit representations of MI which contains cells related to bilateral hand movements, l Cutaneous input at this cortical level may play a role in tactile guidance of volitional arm movements. Our finding that the transition between cortical premotor area 6 and primary motor area 4 was bilaterally activated, and displayed smaller side-toside difference than MI cortex, may reflect the fact that the central representation of the forelimb peripheral fields is distributed bilaterally within the postarcuate area 6, and contralaterally within the precentral cortical area 4.42 The present study demonstrates for the first time that extensive portions of MI and SI, outside the representation of the forelimb, are activated during the performance of a simple visually guided reaching task with one forelimb. The intensive bilateral participation of extended subregions of MI and SI (e.g. lower body-hindlimb and mouth areas) in this simple motor behaviour is surprising. This finding demonstrates that the lower body and the mouth play a very active role during the performance of the task, for the adjustment of body posture and the uptake of liquid, respectively. Given that several populations of taskrelated cells, beyond the forelimb-related ones, are activated during the performance of this simple reaching task, careful interpretation of electrophysiologic and metabolic data is required. For example, subtraction of the metabolic activity map in the ipsilateral from that in the contralateral hemisphere is required for the revelation of the specifically involved forelimb sensorimotor areas. Finally, the bilaterality of effect within the body and mouth areas in the MI and SI cortex is compatible with the described dense callosal connections in the trunk and
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face representations, 24'35 as well as with the reported substantial bilateral i n p u t f r o m the orofacial region to the cortical representation of face.l° CONCLUSION In s u m m a r y , this is the first time t h a t the q u a n t i t a t ive spatial m e t a b o l i c activity p a t t e r n in the somatos e n s o r i m o t o r cortex has been reconstructed in m o n k e y s p e r f o r m i n g a reaching task. T h e continuous, high resolution, 2-D reconstructed m a p o f hemispheric differences in the cortex a r o u n d the central sulcus illustrates for the first time by a noninvasive m e t h o d , the areas of forelimb representation within M I a n d SI in the primate. Moreover, in c o n t r a s t to a long-standing previous proposal, 4 a n d in accordance to o u r recent suggestion, 32 the present results verify the m o t o r control of a reaching forelimb by the contralateral r a t h e r t h a n the ipsilateral hemisphere.
F u r t h e r m o r e , a surprising new finding is the bilateral participation of a n extended p o r t i o n of M I a n d SI (i.e., lower b o d y - h i n d l i m b a n d m o u t h areas of representation) in a relatively simple m o t o r b e h a v i o u r such as u n i m a n u a l reaching to visual targets. Finally, metabolic d a t a in the present f o r m a t of a continuous, high resolution m a p m a y be used as a d a t a b a s e for future image analysis c o m p a r i s o n s with similarly reconstructed m a p s generated during the p e r f o r m a n c e of various other tasks. Thus, task related cell populations, a n d consequently function specific cortical regions m a y be revealed. Acknowledgements--We are grateful to Roberto Caminiti
for allowing us to use his laboratory in Universita degli Studi di Roma "La Sapienza" for part of our study. We thank Catherine Dermon and Stefano Ferraina for excellent technical assistance, Paul B. Johnson, Emmanuel Guigon and Adonis Moschovakis for constructive comments. Work supported by HCM Grant ERBCHRXCT 930266.
REFERENCES
1. Aizawa H., Mushiake H., Inase M. and Tanji J. (1990) An output zone of the monkey primary motor cortex specialized for bilateral hand movement. Expl Brain Res. 82, 219-221. 2. Asanuma H., Arnoid A. and Zarzecki P. (1976) Further study on the excitation of pyramidal tract cells by intracortical microstimulation. Expl Brain Res. 26, 443-461. 3. Asanuma H. and Rosen I. (1972) Topographical organization of cortical efferent zones projecting to distal forelimb muscles in the monkey. Expl Brain Res. 14, 243-256. 4. Brinkman J. and Kuypers H. G. J. M. (1972) Splitbrain monkeys: cerebral control of ipsilateral and contralateral arm, hand, and finger movement. Science 176, 536 539. 5. Brinkman J. and Kuypers H. G. J. M. (1973) Cerebral control of contralateral and ipsilateral ann, hand and finger movements in the split-brain rhesus monkey. Brain 96, 653-674. 6. Darian-Smith C., Darian-Smith I. and Cheema S. S. (1990) Thalamic projections to sensorimotor cortex in the macaque monkey: use of multiple retrograde fluorescent tracers. J. comp. Neurol. 299, 17-46. 7. Gazzaniga M. S. (1964) Cerebral mechanism involved in ipsilateral eye hand use in split-brain monkeys. Expl Neurol. 10, 148 155. 8. Georgopoulos A. P., Caminiti R. and Kalaska J. F. (1984) Static spatial effects in motor cortex and area 5: quantitative relations in a two-dimensional space. Expl Brain Res. 54, 446-454. 9. Georgopoulos A. P., Kalaska J. F., Caminiti R. and Massey J. T. (1982) On the relations between the direction of two-dimensional ann movements and cell discharge in primate motor cortex. J. Neurosci. 2, 1527-1537. 10. Huang C.-S., Hiraba H. and Sessle B. J, (1989) Input output relationships of the face motor cortex in the monkey (Macaca fascicularis). J. Neurophysiol. 61, 350 362. I 1. Hubel D. H., Wiesel T. N. and Stryker M. P. (1978) Anatomical demonstration of orientation columns in Macaque monkey. J. comp. Neurol. 177, 361-380. 12. Humphrey D. R. and Tanji J. (1991) What features of voluntary motor control are encoded in the neuronal discharge of different cortical motor areas? In Motor Control: Concepts and Issues (eds Humphrey D. R. and Freund H.-J.), pp. 413-444. Wiley, Chichester. 13. Hungerbuhler J. P., Saunders J. C., Greenberg J. and Reivich M. (1981) Functional neuroanatomy of the auditory cortex studied with [2-14C]-deoxyglucose. Expl Neurol. 71, 104-121. 14. Iwamura Y., Tanaka M., Hikosaka K. and Sakamoto T. (1980) Overlapping representation of fingers in area 2 of the somatosensory cortex of the conscious monkey. Brain Res. 197, 516-520. 15. Iwamura Y., Tanaka K., Hikosaka K. and Sakamoto T. (1983) Functional subdivisions representing different finger regions in area 3 of the first somatosensory cortex of the conscious monkey. Expl Brain Res. 51, 315 326. 16. Iwamura Y., Tanaka K., Sakamoto T. and Hikosaka K. (1983) Converging patterns of finger representation and complex response properties of neurons in area 1 of the first somatosensory cortex of the conscious monkey. Expl Brain Res. 51, 327-337. 17. Johnson P. B., Angelucci A., Ziparo R., Minciacchi D., Bentivoglio M. and Caminiti R. (1989) Segregation and overlap of callosal and association neurons in frontal and parietal cortices of primates. A spectral and coherency analysis. J. Neurosci. 9, 2313 2326. 18. Jones E. G., Coulter J. D. and Hendry S. H. C. (1978) Intracortical connectivity of architectonic fields in the somatic sensory, motor and parietal cortex of monkeys. J. comp. Neurol. 181, 291-348. 19. Jones E. G., Coulter J. D. and Wise S. P. (1979) Commissural columns in the sensory-motor cortex of monkeys. J. comp. Neurol. 188, 113-136. 20. Jones E. G. and Wise S. P. (1977) Size, laminar, and columnar distribution of efferent ceils in the sensory-motor cortex of monkeys. J. comp. Neurol. 175, 391-438.
Activity pattern in sensorimotor cortex during reaching
333
21. Juliano S. L., Hand P. J. and Whitsel B. L. (1981) Patterns of increased metabolic activity in somatosensory cortex of monkeys Macaeafascicularis, subjected to controlled cutaneous stimulation: a 2-deoxyglucose study. J. Neurophysiol. 46, 1260-1284. 22. Kalaska J. F., Cohen D. A. D., Hyde M. L. and Prud'homme M. (1989) A comparison of movement direction-related versus load direction-related activity in primate motor cortex, using a two-dimensional reaching task. J. Neurosci. 9, 2080 2102. 23. Kennedy C., Sakurada O., Shinohara M., Jehle J. and SokoloffL. (1978) Local cerebral glucose utilization in the normal conscious macaque monkey. Ann. Neurol. 4, 293001. 24. Killackey H. P., Gould H. J., Cusick C. G., Pons T. P. and Kaas J. H. (1983) The relation of the corpus callosum connections to architectonic fields and body surface maps in sensorimotor cortex of new and old world monkeys. J. comp. Neurol. 219, 384-419. 25. Kuypers H. G. J. M. (1964) The descending pathways to the spinal cord, their anatomy and function. In Progress in Brain Research, Vol. 11, Organization o f the Spinal Cord (eds Eccles J. C. and Schade J. C.), pp. 188-202. Elsevier, Amsterdam. 26. Kuypers H. G. J. M. and Brinkman J. (1970) Precentral projections of different parts of the spinal intermediate zone in the rhesus monkey. Brain Res. 24, 29-48. 27. Kwan H. C., MacKay W. A., Murphy J. T. and Wong Y. C. (1978) Spatial organization of precentral cortex in awake primates. II. Motor outputs. J. Neurophysiol. 41, 1120-1131. 28. Liu C. N. and Chambers W. W. (1964) An experimental study of the cortico-spinal system in the monkey (Macaca mulatta). The spinal pathways and preterminal distribution of degenerating fibers following discrete lesions. J. comp. Neurol. 123, 257-284. 29. Myers R. E., Sperry R. W. and McGurdy N. M. (1962) Neuronal mechanisms in visual guidance of limb movement. Arch. Neurol. 7, 195-202. 30. Nelson R. J. and Kaas J. H. (1981) Connections of the ventroposterior nucleus of the thalamus with the body surface representations in cortical areas 3b and 1 of the cynomolgus macaque (Macaca fascicularis). J. comp. Neurol. 199, 29-64. 31. Nelson R. J., Sur M., Fellman D. J. and Kaas J. H. (1980) Representations of the body surface in postcentral parietal cortex of Macaca fascicularis. J. comp. Neurol. 192, 611-643. 32. Savaki H. E., Kennedy C., Sokoloff L. and Mishkin M. (1993) Visually guided reaching with the forelimb contralateral to a "blind" hemisphere: a metabolic mapping study in monkeys. J. Neurosci. 13, 2772-2789. 33. Schwartz A. B., Kettner R. E. and Georgopoulos A. P. (1988) Primate motor cortex and free arm movements to visual targets in three-dimensional space. I. Relations between single cell discharge and direction of movement. J. Neurosci. 8, 2913-2927. 34. Sessle B. J. and Wiesendanger M. (1982) Structural and functional definition of the motor cortex in the monkey (Macaca fascicularis). J. Physiol. 323, 245~65. 35. Shanks M. F., Pearson R. C. A. and Powell T. P. S. (1985) The callosal connections of the primary somatic sensory cortex in the monkey. Brain Res. Rev. 9, 43-65. 36. Shanks M. F. and Powell T. P. S. (1981) An electron microscopy study of the termination of thalamocortical fibres in area 3b, 1 and 2 of the somatic sensory cortex in the monkey. Brain Res. 218, 35-47. 37. Sokoloff L., Reivich M., Kennedy C., Des Rosiers M. H., Patlak C. S., Pettigrew K. S., Sakurada O. and Shinohara M. (1977) The [~4C]-deoxyglucose method for the measurement of local cerebral glucose utilization: theory, procedure, and normal values in the conscious and anesthetized albino rat. J. Neurochem. 28, 879-916. 38. Tigges J., Nakagawa S. and Tigges M. (1979) Efferents of area 4 in a South American monkey (Saimiri). I. Terminations in the spinal cord. Brain Res. 171, 1-10. 39. Tokuno H. and Tanji J. (1993) Input organization of distal and proximal forelimb areas in the monkey primary motor cortex: a retrograde double labeling study. J. comp. Neurol. 333, 199-209. 40. Tommerdahl M., Favorov O. V., Whitsel B. L., Nakhle B. and Gonchar Y. A. (1993) Minicolumnar activation patterns in cat and monkey SI cortex. Cereb. Cortex 3, 399-411. 41. Vogt B. A. and Pandya D. N. (1977) Cortico-cortical connections of somatic sensory cortex (areas 3, 1 and 2) in the rhesus monkey. J. comp. Neurol. 177, 179-192. 42. Wong Y. C., Kwan H. C., MacKay W. A. and Murphy J. T. (1978) Spatial organization of precentral cortex in awake primates. I. Somatosensory inputs. J. Neurophysiol. 41, 1107 1119. 43. Woolsey C. N., Settlage P. H., Meyer D. R., Sencer W., Pinto Hamuy T. and Travis A. M. (1952) Patterns of localization in precentral and "supplementary" motor areas and their relation to the concept of a premotor area. Res. Pubis Ass. Res. nerv. ment. Dis. 30, 233~64. (Accepted 23 November 1995)
0306-4522(95)00516-1
Neuroscience Vol. 72, No. 2, pp. 325 333, 1996 Elsevier ScienceLtd Copyright © 1996 IBRO Printed in Great Britain. All rights reserved 0306-4522/96 $15.00 + 0.00
M E T A B O L I C A C T I V I T Y P A T T E R N IN THE M O T O R A N D S O M A T O S E N S O R Y C O R T E X OF M O N K E Y S P E R F O R M I N G A V I S U A L L Y G U I D E D R E A C H I N G T A S K WITH ONE FORELIMB* Y. D A L E Z I O S , V. C. R A O S and H. E. S A V A K I t Laboratory of Functional Brain Imaging, Department of Basic Sciences, Division of Medicine, School of Health Sciences, University of Crete, P.O. Box 1393, GR-71110 Iraklion, Crete, Greece A~traet--The [~4C]deoxyglucose method was used to map the metabolic activity in the primary somatosensory and motor cortex in monkeys (Macaca nernestrina) performing a unimanual task. The task required visually guided reaching and target holding at a rate of about 10 movements per min. The entire dorsoventral extent of the cortical region lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulci was. reconstructed on the sagittal plane, from horizontal sections aligned on the fundus of the central sulcus. The metabolic mapping of the control monkey demonstrated homogeneous activity all around the central sulcus, bilaterally. The mapped activity in the performing monkeys displayed two different patterns. The first pattern, contralateral to the moving forelimb, was characterized by several discrete regions of increased metabolic activity, which were symmetrically distributed in a mirror image fashion around the fundus of the central sulcus. These activated regions correspond to the lower body, forelimb, and mouth areas of representation of body parts in previously reported maps in primary motor and somatosensory cortical areas. The second activity pattern ipsilateral to the moving forelimb, displayed activated somatosensory and motor regions corresponding only to the lower body, and mouth representations. Our study provides a continuous, high resolution map of activity pattern in the entire primary motor and somatosensory cortices, which demonstrates that the reaching forelimb is controlled by a discrete subregion in the contralateral somatosensorimotor cortex, whereas other subregions of body representation are actively involved, bilaterally, during the performance of a relatively simple motor behaviour. Key words: primary motor cortex, primary somatosensory cortex, central sulcus, reaching movements, [J4C]deoxyglucose.
Ipsilateral corticospinal fibres, originating from the trunk and proximal limb areas of the m o t o r cortex 5,25,26,2s'3s have been considered responsible for mediating control over the ipsilateral f o r e l i m b : '25 The long standing paradox of a split-brain monkey reaching accurately to a visual target with the forelimb contralateral to its "blind" hemisphere 7'29 has been explained by the implication of this descending corticospinal pathway. It has been proposed that control of the reaching forelimb in the split-brain monkey is shifted from the visually deafferented contralateral hemisphere to the visually intact ipsilateral o n e : The 2-[14C]deoxyglucose ([14C]DG) method applied on intact and split-brain monkeys performing a unimanual reaching task after visual pattern discrimination, revealed activation of the somatosensorimotor cortex in the hemisphere contralateral to the moving
forelimb, irrespective of whether this hemisphere was intact or visually deafferented. 32 Thus, in contrast to Brinkman and Kuypers' proposal, 4 it was recently suggested that visually guided reaching with the forelimb contralateral to a "blind" hemisphere is subserved by that hemisphere's somatosensorimotor cortex and not by the cortex of the ipsilateral "seeing" hemisphere. 3z The objective of the present study was to further examine the underlying mechanisms of reaching, by providing a detailed, quantitative, bilateral, pictorial view of the metabolic pattern of activity within the entire precentral primary m o t o r (MI) and postcentral primary somatosensory (SI) cortex in monkeys performing a unimanual, visually guided, arm reaching and key pressing task. This allows us to avoid averaging glucose utilization rates within relatively wide M I subregions, and to obtain measures of metabolic activity within the specific m o t o r areas of body representation (i.e. mouth, hand, arm, lower body). To this end, the distribution of the [14C]DG labelling in the cortex around the central sulcusof each hemisphere in horizontal autoradiographic brain sections (three adjacent 20-/~m-thick sections
*Part of this work was presented at the 19th annual meeting of the European Neuroscience Association. tTo whom correspondence should be addressed. Abbreviations: [14C]DG, [14C]deoxyglucose; LCGU, local cerebral glucose utilization; L/R % DIF, left to right hemispheric differences; MI, primary motor cortex; SI, primary somatosensory cortex. 325
326
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every 140/~m) of control and reaching monkeys was r e c o n s t r u c t e d in t w o d i m e n s i o n s , o n t h e s a g i t t a l plane.
EXPERIMENTAL PROCEDURES
Subjects Three adult female Macaca nemestrina monkeys weighing between 3.5 and 4.0 kg were used. The first monkey was trained to perform the visually guided reaching task with its right forelimb. The second monkey was trained to perform the same task with its left forelimb. The third monkey was an untrained normal control, seating in front of the nonfunctioning test panel and receiving neither visual stimuli nor liquid reward during the [14C]DG experiment. All three monkeys had their head fixed, while a water delivery tube was positioned close to the m o u t h of the two performing animals. Task and apparatus The test panel in front of the monkey contained two push-buttons which could be illuminated from behind. They were spaced 8.7 cm from each other and arranged in a line 45 ° distal to the frontal plane, in 3-D space. The central, start-button was located in the midsagittal plane (0 °) at shoulder height and 25 cm from the monkey, whereas the peripheral, target-button was located 45 ° to the right or to the left, for the monkey reaching with the right or the left forelimb, respectively. The intertrial intervals ranged between 1 and 1.5 s. The monkey was required to press and hold the illuminated central button for 1.5 2.5 s, until this was turned off and the peripheral button was lit up. Within the specified upper limit of reaction and movement time (1.35 s) the monkey was required to release the central and press the peripheral button. After holding the peripheral button for 1-1.5 s, a liquid reward was delivered. The two trained monkeys reached a performance criterion of > 90% correct responses, resulting in 8 12 single-directional movements per min during the 45 min of the [14C]DG experimental period. Measurement o f glucose utilization On the experimental day, monkeys were subjected to femoral vein and artery catheterization under ketamine hydrochloride anaesthesia (20 mg/kg, i.m.). The monkeys were allowed 4-5 h to recover from anaesthesia. The procedure used for determining the local cerebral glucose utilization ( L C G U ) was the same as that previously described. 32 The measurement of L C G U was initiated by the intravenous injection o f [t4C]DG as a pulse of 100 # Ci/kg of, 2-deoxy-D-[1-14C]glucose (specific activity 50-55 mCi/mmol, NEN) dissolved in physiological saline. Timed arterial samples were collected from the catheterized femoral artery during the succeeding 45 min at a predetermined schedule. Plasma [~4C]DG concentrations were determined by liquid scintillation spectrometry, and plasma glucose concentrations were measured with a Beckman Glucose Analyser. At 45 min after the [14C]DG administration, the animal was killed by intravenous injections of 50 m g o f sodium thiopental in 5 ml saline, and then a saturated potassium chloride solution to stop the heart. The brain was removed, frozen in Freon at - 5 0 ° C , and stored at - 7 0 ° C until sectioned for autoradiography. Three 20-/~m thick adjacent horizontal sections of brain were cut every 1 4 0 # m in a cryostat at - 2 0 ° C , and autoradiographs were prepared by exposing these sections (together with precalibrated [~4C]standards) with medical X-ray film (Kodak OM1) in X-ray cassettes. The intermediate sections, which were not cut for autoradiography, were used for histologic staining. Quantitative densitometric analysis of autoradiographs was carried out with a computerized image-processing system (Imaging Research Inc., Ontario, Canada), which
allowed integration of the L C G U values over the entire extent of each area of interest. L C G U was calculated from the kinetic constants for the monkey, 23 by the operational equation of the [t4C]DG method. 37 Normalization of the L C G U values was based on the average white matter value pooled across all three monkeys (16/~mol/100g/min). Left to right hemispheric differences (L/R % D I F ) were calculated, and analysed by the paired t-test, as previously described. 32 In a similar way, per cent activation in each region (i) within each hemisphere in the active (A) monkeys was calculated in comparison to the value of the homologous cortical area in the control inactive (C) monkey, by the equation: %Ci = ( A i ~ i)/C i * 100. Two dimensional reconstruction A two dimensional reconstruction of the metabolic activity pattern within the entire dorsoventral extent of the cortical area lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulci in each hemisphere was generated on the sagittal plane. The distribution of activity in the anteroposterior extent in each horizontal section was determined by measuring L C G U values pixel by pixel (resolution, 35 50 ~tm/pixel) along a line parallel to the surface of the cortex approximately midway through its depth (covering cortical layers I I V , see Fig. 1B, DR). The data arrays resulting from anteroposterior image segmentation in adjacent horizontal sections were aligned around the fundus of the central sulcus. The plotting resolution of both anteroposterior and dorsoventral dimensions was 100~m. Occasional missing data arrays in the dorsoventral dimension were filled using linear interpolation between neighbouring values. The m a p of hemispheric differences was obtained by computer generated subtraction of the digitized ipsilateral metabolic m a p from the one contralateral to the moving arm, after alignment of the two maps around the fundus of the central sulcus. The activated regions in the precentral and the postcentral banks in our m a p s were compared to previously reported MI and SI maps of body representation. Specifically, the lower body-hindlimb (b) representation in the MI m a p of Fig. 23 published by Woolsey 43 covers 27% (3.7 cm) of the total mediolateral extent of the precentral bank (13.5 cm). The shoulder-arm (a) representation covers 18% (2.4 cm), the hand-digits (h) area 21% (2.8 cm), and the m o u t h (m) area 34% (4.6 cm) in the same map. For reasons of comparison, in Fig. 1A (Rc), the borders of the respective relative extents in our maps are marked on the bottom abscissa which represents the dorsoventral extent of the central sulcus. These markings should be considered as only indicative borders, not only because of the way they were estimated, but also because of the known overlaps between cortical motor areas controlling distinct body parts. The relative extent of the same areas in the postcentral bank were similarly estimated to be, b = 32%, a = 22%, h = 24%, and m = 22% in SI-3b m a p of Fig. 1 published by K a a s ' group. 3~ In Fig. IA (Rc), the respective relative extents in our m a p s are labelled on the top abscissa. Unfortunately, histologic staining of the frozen sections from the nonperfused brains in our study, did not allow for discrimination of cytoarchitectural borders. Thus, the boundaries between areas 3a, 3b, 1, and 2 indicated in Fig. 1A (Rc) were calculated according to those reported earlier (Figs 3 and 8 of Juliano et al.2t). These labellings should also be considered as only indicative borders. RESULTS Both monkeys performing visually guided reaching m o v e m e n t s d u r i n g t h e [14C]DG e x p e r i m e n t d i s p l a y e d m e t a b o l i c a c t i v a t i o n in M I ( a r e a 4) a n d SI ( a r e a s 3, a n d 1-2) b i l a t e r a l to t h e m o v i n g f o r e l i m b w h e n c o m p a r e d w i t h t h e c o n t r o l m o n k e y (see % C in
Activity pattern in sensorimotor cortex during reaching
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Table 1). Smaller, bilateral, metabolic activation was measured in the transition of premotor area 6 to primary motor area 4, lying between the posterior crown of the arcuate and the anterior crown of the central sulcus. Paired t-test statistics revealed that the metabolic activation within MI and SI in the hemisphere contralateral to the moving forelimb was always significantly higher than that in the ipsilateral homologous cortical area (see L/R and R/L%DIF in Table 1). In contrast, there was no consistently significant side to side difference within the region of transition of area 6 to area 4. In summary, the quantitative estimation of average glucose utilization value within the entire extent of MI and SI demonstrated that moving one forelimb to a visual target activates the primary motor and somatosensory cortices bilaterally, although the contralateral side is significantly more activated than the ipsilateral one. The question remained, which areas of body representation in MI and SI reflect the measured activation? Is it, simply, the forelimb area of representation which is bilaterally activated displaying higher contra- than ipsilateral values, or the distribution of metabolic activation within the different areas of representation is more complex? We attempted to answer this question by the two dimensional (2-D) reconstruction of metabolic maps of the cortex around the central sulcus. The 2-D reconstructed metabolic maps exhibit different global spatiointensive patterns depending on (i) the performance on the task, and (ii) the side of the hemisphere relative to the moving forelimb. The reconstructed maps of the cortex around the central sulcus in the left and right hemispheres (L and R) of the inactive control monkey (c) are both rather homogeneous (Fig. IA: Lc and Rc). The metabolic activity in the two unimanually performing monkeys display two different patterns. The first activity pattern, which is observed contralateral to the moving forelimb in both active monkeys, displays a fish-bone shape around the fundus of the central sulcus. In other words, this pattern is characterized by several discrete regions of increased metabolic activity, which are symmetrically distributed as mirror images around the fundus of the central sulcus, and which extend in the precentral and postcentral banks as well as beyond the anterior and posterior crowns of the sulcus (Figs 1A and 1B: CONTRA). In general, the metabolic activations in the precentral bank which correspond to MI regions are lower than those in the postcentral mirror image areas which correspond to SI regions. The symmetric activation pattern around the fundus of the central sulcus refers to a symmetry around the approximate MI-SI border, which is similar to that illustrated in Woolsey's homuncular representation. Comparison of our metabolic maps with previously reported MI and SI somatotopic maps revealed that the activated regions in the somatosensorimotor cortex contralaterai to the moving forelimb cover all body part representations, i.e. the
328
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lower body-hindlimb (b), the arm-shoulder (a), the hand-digits (h), and the mouth (m) areas (see Fig. 1A: Rc for indicative dorsoventral levels of body part representations). The second activity pattern, which is observed ipsilateral to the moving forelimb in both active monkeys, displays precentral MI and postcentral SI regions, which are activated symmetrically around the fundus and correspond mainly to the lower body-hindlimb and mouth areas (Figs 1A and I B: IPSI). In summary, during a simple, liquid rewarded, unimanual, visuomotor task, (i) the forelimb representation within the MI and SI is activated only in the hemisphere contralateral to the moving arm, whereas (ii) the lower body and the mouth representations are activated within the MI and SI in both hemispheres. Area 3a, which is located around the depth of the fundus, is more active in both hemispheres in the monkey moving the left than in the monkey moving the right forelimb. However, the maps of hemispheric differences in the two reaching monkeys are similar, demonstrating specific activation only within the forelimb area in both MI and SI (Figs 1A and IB: CONTRA-IPSI). Four metabolic bands parallel to the posterior crown of the central sulcus are observed in the activated SI-forelimb area, with a peak to peak distance varying between 2 and 5 mm. Some of these bands extend beyond the posterior crown, within the SI area 2. Computer generated magnification of the activated MI-forelimb region, reconstructed at a higher resolution (28#m/pixel), displayed bands symmetric to the SI-forelimb ones as to the axis (fundus) of the central sulcus, and parallel to the anterior crown (Fig. 2). The region of cortical transition of area 6 to area 4 in both hemispheres of both performing monkeys is more active and labelled in a less uniform manner than the homologous region in the control monkey. Although the effect within the transition of area 6 to area 4 appears to be mostly bilateral, a region which is specifically activated in the hemisphere contralateral to the moving forelimb is differentiated in the map of hemispheric differences in both reaching monkeys. This region is located caudal to the posterior crown of the arcuate sulcus and at the same dorsoventral level with the MI-forelimb area (Figs 1A and 1B: CONTRA-IPSI).
DISCUSSION
The present study is the first to provide a quantitative, bilateral, pictorial view of the metabolic pattern of activity within the cerebral neocortex around the central sulcus (cortex lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulcus) in monkeys performing a visually guided reaching task with one forelimb. The observed symmetry between the MI and SI patterns of activity as to the fundus of the central sulcus is in
accordance with the overall macroscopic somatotopic pattern in Woolsey's homuncular representations in MI and SI. 43 Comparison of our data with existing functional maps of the body representation around the central sulcus 3~'43 demonstrates for the first time that the areas corresponding to the lower body and the mouth representations are activated in the MI. Thus, the present results verify the motor control of a reaching forelimb by the contralateral rather than the ipsilateral hemisphere, in contrast to a previous proposal based on the anatomic projections from MI to ventral horn cells innervating the proximal musculature of the ipsilateral limb, 4 and in accordance with our recent suggestion. 32 Within the area of SI-forelimb representation contralateral to the moving forelimb, "the activated patches observed in the individual horizontal autoradiographic sections formed active bands in the reconstructed metabolic map. L C G U metabolic studies of the visual, auditory, and somatosensory cortex have demonstrated labelling patterns consisting of "columns" or "strips". ~'~3"2~The active "strips" in SI are reported to vary with the stimulus location and the field size on the skin. 2~ Discrete forelimb skin stimuli were reported to evoke elongated active [14C]DG "modules" within an extensive region of SI, with a peak to peak distance 2-6mm. 4° This is consistent with the distance between two adjacent metabolically active bands in the SI-forelimb representation in our study. Observed bands in our study may be related to the reported cortical inpuwoutput clusters associated with callosal, associational, and thalamocortical projections. 17"~9'2° However, the reported gradient of callosal projections, with area 3b displaying few, area 1 intermediate, and area 2 dense connections, 24 is the inverse of the intensity of metabolic activity observed in our map. Also, the distribution and density of the association connections within areas 3b, 1, and 2 ~8"4~do not correspond to the LCGU spatiointensive pattern observed in this study. The pattern we observed is more consistent with the thalamocortical projection system, which is heavy in areas 3a, 3b, and less dense in areas 1, 2. 30.36 The observed metabolic fractionation of the SI-forelimb area into elongated units may reflect the continuous representation of each activated forelimb segment across the distinct maps in SI subregions. 3j Our finding that, more active bands are located between the fundus and the posterior crown of the central sulcus (area 3), fewer ones are located around the crown (area 1), and there is a lack of discretely activated bands caudal to this crown (area 2), is compatible with the reported discrete representation in area 3, ~5 wide field representation in area 1, ~6 and extensively overlapping representation in area 2 where multiple functions apart from body parts are represented. 14 Within the area of MI-forelimb representation, although no activated patches were apparent by visual inspection of the individual horizontal
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Fig. 1. Two dimensional reconstruction of the LCGU values (in/~mol/100 g/min) in the cortical region lying between the posterior crown of the arcuate (lower border) and the anterior crown of the intraparietal sulcus (upper border of reconstructed images). Solid line at zero anteroposteriority represents the fundus of the central sulcus, which was used as the landmark for alignment of adjacent horizontal sections. Dotted lines represent the anterior (lower) and the posterior (upper) crowns of the central sulcus. (A) CONTRA and IPSI, left and right hemispheres, respectively, in the monkey reaching with the right forelimb. CONTRA-IPSI, map generated after subtraction of the reconstructed ipsilateral central sulcus from the one contralateral to the moving forelimb. Lc and Rc, left and right hemispheres in the control inactive monkey. Approximate boundaries of body part representations in the precentral MI and postcentral SI cortical areas are labelled in the bottom and top abscissae of Rc map, respectively: a, arm-shoulder; b, body-hindlimb; h, hand-digits; m, mouth. Indicative borders between areas 3a, 3b, 1, and 2 are marked at the level of the forelimb representation in SI. LCGU, scale of local cerebral glucose utilization values in all reconstructed maps but the one representing the interhemispheric differences. LCGU Dif, scale of values in the maps representing the interhemispheric differences. (B) IPSI and CONTRA, left and right hemispheres, respectively, in the monkey reaching with the left forelimb. CONTRA-IPSI, as in case A above. DR, diagrammatic representation of the anteroposterior extent of the reconstructed cortical area (dashed line) in horizontal sections at 10 dorsoventral levels spaced about 2 mm apart. A, anterior; AS, arcuate sulcus; CS, central sulcus; D, dorsal; I, intraparietal sulcus; P, posterior; V, ventral.
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Dorsoventral Extent (mm) Fig. 2. Computer generated magnification of the spatiointensive activation pattern (resolution of 28/~m/pixel) within the SI and MI forelimb representation areas in the hemisphere contralateral to the moving arm (monkey illustrated in Fig. 1B: CONTRA). The bands displayed within the MI-forelimb region are symmetric to the SI-forelimb ones as to the axis (fundus) of the central sulcus, and parallel to the anterior crown.
autoradiographic sections, a metabolically active region was observed in the caudal zone of the precentral bank contralateral to the moving forelimb within the reconstructed metabolic maps. This finding is compatible with the suggestion that neurons in caudal MI contribute to proprioceptive and cutaneous guidance of ongoing movements. 12 The bands seen within the activated MI-forelimb region at a
331
higher resolution, were not arranged in a concentric "ringlike''42 or "horseshoelike ''34 pattern, and did not span both areas 4 and 6. 34,42Instead, these bands were parallel to each other, and displayed an anteroposterior periodicity falling within the range of dimensions of both the somatosensory input and motor output clusters reported in M I . 2'3'27 However, given that (i) the anterior, and posterior ventrolateral, as well as the ventromedial thalamic neurons, which mediate input from the globus pallidus, the cerebellum, and the substantia nigra, respectively, converge on single cortical modules in MI, 6 (ii) the projection of the supplementary and cingulate motor areas to the forelimb region of MI has no precise topographical organisation,39 and (iii) several intrinsic connections exist inside the MI, 39 the activated bands in our study may not reflect somatotopic representation based on input and output. Alternatively, these bands may represent the spatial organization of motor cortical neurons encoding specific kinematic or dynamic parameters of reaching movements.8'9'22'33The bilaterally activated band we observed in the ventral part of MI-forelimb area in the reaching monkeys, complements the neurophysiologic finding that a specialized efferent zone exists between the face and digit representations of MI which contains cells related to bilateral hand movements, l Cutaneous input at this cortical level may play a role in tactile guidance of volitional arm movements. Our finding that the transition between cortical premotor area 6 and primary motor area 4 was bilaterally activated, and displayed smaller side-toside difference than MI cortex, may reflect the fact that the central representation of the forelimb peripheral fields is distributed bilaterally within the postarcuate area 6, and contralaterally within the precentral cortical area 4.42 The present study demonstrates for the first time that extensive portions of MI and SI, outside the representation of the forelimb, are activated during the performance of a simple visually guided reaching task with one forelimb. The intensive bilateral participation of extended subregions of MI and SI (e.g. lower body-hindlimb and mouth areas) in this simple motor behaviour is surprising. This finding demonstrates that the lower body and the mouth play a very active role during the performance of the task, for the adjustment of body posture and the uptake of liquid, respectively. Given that several populations of taskrelated cells, beyond the forelimb-related ones, are activated during the performance of this simple reaching task, careful interpretation of electrophysiologic and metabolic data is required. For example, subtraction of the metabolic activity map in the ipsilateral from that in the contralateral hemisphere is required for the revelation of the specifically involved forelimb sensorimotor areas. Finally, the bilaterality of effect within the body and mouth areas in the MI and SI cortex is compatible with the described dense callosal connections in the trunk and
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Y. Dalezios et al.
face representations, 24'35 as well as with the reported substantial bilateral i n p u t f r o m the orofacial region to the cortical representation of face.l° CONCLUSION In s u m m a r y , this is the first time t h a t the q u a n t i t a t ive spatial m e t a b o l i c activity p a t t e r n in the somatos e n s o r i m o t o r cortex has been reconstructed in m o n k e y s p e r f o r m i n g a reaching task. T h e continuous, high resolution, 2-D reconstructed m a p o f hemispheric differences in the cortex a r o u n d the central sulcus illustrates for the first time by a noninvasive m e t h o d , the areas of forelimb representation within M I a n d SI in the primate. Moreover, in c o n t r a s t to a long-standing previous proposal, 4 a n d in accordance to o u r recent suggestion, 32 the present results verify the m o t o r control of a reaching forelimb by the contralateral r a t h e r t h a n the ipsilateral hemisphere.
F u r t h e r m o r e , a surprising new finding is the bilateral participation of a n extended p o r t i o n of M I a n d SI (i.e., lower b o d y - h i n d l i m b a n d m o u t h areas of representation) in a relatively simple m o t o r b e h a v i o u r such as u n i m a n u a l reaching to visual targets. Finally, metabolic d a t a in the present f o r m a t of a continuous, high resolution m a p m a y be used as a d a t a b a s e for future image analysis c o m p a r i s o n s with similarly reconstructed m a p s generated during the p e r f o r m a n c e of various other tasks. Thus, task related cell populations, a n d consequently function specific cortical regions m a y be revealed. Acknowledgements--We are grateful to Roberto Caminiti
for allowing us to use his laboratory in Universita degli Studi di Roma "La Sapienza" for part of our study. We thank Catherine Dermon and Stefano Ferraina for excellent technical assistance, Paul B. Johnson, Emmanuel Guigon and Adonis Moschovakis for constructive comments. Work supported by HCM Grant ERBCHRXCT 930266.
REFERENCES
1. Aizawa H., Mushiake H., Inase M. and Tanji J. (1990) An output zone of the monkey primary motor cortex specialized for bilateral hand movement. Expl Brain Res. 82, 219-221. 2. Asanuma H., Arnoid A. and Zarzecki P. (1976) Further study on the excitation of pyramidal tract cells by intracortical microstimulation. Expl Brain Res. 26, 443-461. 3. Asanuma H. and Rosen I. (1972) Topographical organization of cortical efferent zones projecting to distal forelimb muscles in the monkey. Expl Brain Res. 14, 243-256. 4. Brinkman J. and Kuypers H. G. J. M. (1972) Splitbrain monkeys: cerebral control of ipsilateral and contralateral arm, hand, and finger movement. Science 176, 536 539. 5. Brinkman J. and Kuypers H. G. J. M. (1973) Cerebral control of contralateral and ipsilateral ann, hand and finger movements in the split-brain rhesus monkey. Brain 96, 653-674. 6. Darian-Smith C., Darian-Smith I. and Cheema S. S. (1990) Thalamic projections to sensorimotor cortex in the macaque monkey: use of multiple retrograde fluorescent tracers. J. comp. Neurol. 299, 17-46. 7. Gazzaniga M. S. (1964) Cerebral mechanism involved in ipsilateral eye hand use in split-brain monkeys. Expl Neurol. 10, 148 155. 8. Georgopoulos A. P., Caminiti R. and Kalaska J. F. (1984) Static spatial effects in motor cortex and area 5: quantitative relations in a two-dimensional space. Expl Brain Res. 54, 446-454. 9. Georgopoulos A. P., Kalaska J. F., Caminiti R. and Massey J. T. (1982) On the relations between the direction of two-dimensional ann movements and cell discharge in primate motor cortex. J. Neurosci. 2, 1527-1537. 10. Huang C.-S., Hiraba H. and Sessle B. J, (1989) Input output relationships of the face motor cortex in the monkey (Macaca fascicularis). J. Neurophysiol. 61, 350 362. I 1. Hubel D. H., Wiesel T. N. and Stryker M. P. (1978) Anatomical demonstration of orientation columns in Macaque monkey. J. comp. Neurol. 177, 361-380. 12. Humphrey D. R. and Tanji J. (1991) What features of voluntary motor control are encoded in the neuronal discharge of different cortical motor areas? In Motor Control: Concepts and Issues (eds Humphrey D. R. and Freund H.-J.), pp. 413-444. Wiley, Chichester. 13. Hungerbuhler J. P., Saunders J. C., Greenberg J. and Reivich M. (1981) Functional neuroanatomy of the auditory cortex studied with [2-14C]-deoxyglucose. Expl Neurol. 71, 104-121. 14. Iwamura Y., Tanaka M., Hikosaka K. and Sakamoto T. (1980) Overlapping representation of fingers in area 2 of the somatosensory cortex of the conscious monkey. Brain Res. 197, 516-520. 15. Iwamura Y., Tanaka K., Hikosaka K. and Sakamoto T. (1983) Functional subdivisions representing different finger regions in area 3 of the first somatosensory cortex of the conscious monkey. Expl Brain Res. 51, 315 326. 16. Iwamura Y., Tanaka K., Sakamoto T. and Hikosaka K. (1983) Converging patterns of finger representation and complex response properties of neurons in area 1 of the first somatosensory cortex of the conscious monkey. Expl Brain Res. 51, 327-337. 17. Johnson P. B., Angelucci A., Ziparo R., Minciacchi D., Bentivoglio M. and Caminiti R. (1989) Segregation and overlap of callosal and association neurons in frontal and parietal cortices of primates. A spectral and coherency analysis. J. Neurosci. 9, 2313 2326. 18. Jones E. G., Coulter J. D. and Hendry S. H. C. (1978) Intracortical connectivity of architectonic fields in the somatic sensory, motor and parietal cortex of monkeys. J. comp. Neurol. 181, 291-348. 19. Jones E. G., Coulter J. D. and Wise S. P. (1979) Commissural columns in the sensory-motor cortex of monkeys. J. comp. Neurol. 188, 113-136. 20. Jones E. G. and Wise S. P. (1977) Size, laminar, and columnar distribution of efferent ceils in the sensory-motor cortex of monkeys. J. comp. Neurol. 175, 391-438.
Activity pattern in sensorimotor cortex during reaching
333
21. Juliano S. L., Hand P. J. and Whitsel B. L. (1981) Patterns of increased metabolic activity in somatosensory cortex of monkeys Macaeafascicularis, subjected to controlled cutaneous stimulation: a 2-deoxyglucose study. J. Neurophysiol. 46, 1260-1284. 22. Kalaska J. F., Cohen D. A. D., Hyde M. L. and Prud'homme M. (1989) A comparison of movement direction-related versus load direction-related activity in primate motor cortex, using a two-dimensional reaching task. J. Neurosci. 9, 2080 2102. 23. Kennedy C., Sakurada O., Shinohara M., Jehle J. and SokoloffL. (1978) Local cerebral glucose utilization in the normal conscious macaque monkey. Ann. Neurol. 4, 293001. 24. Killackey H. P., Gould H. J., Cusick C. G., Pons T. P. and Kaas J. H. (1983) The relation of the corpus callosum connections to architectonic fields and body surface maps in sensorimotor cortex of new and old world monkeys. J. comp. Neurol. 219, 384-419. 25. Kuypers H. G. J. M. (1964) The descending pathways to the spinal cord, their anatomy and function. In Progress in Brain Research, Vol. 11, Organization o f the Spinal Cord (eds Eccles J. C. and Schade J. C.), pp. 188-202. Elsevier, Amsterdam. 26. Kuypers H. G. J. M. and Brinkman J. (1970) Precentral projections of different parts of the spinal intermediate zone in the rhesus monkey. Brain Res. 24, 29-48. 27. Kwan H. C., MacKay W. A., Murphy J. T. and Wong Y. C. (1978) Spatial organization of precentral cortex in awake primates. II. Motor outputs. J. Neurophysiol. 41, 1120-1131. 28. Liu C. N. and Chambers W. W. (1964) An experimental study of the cortico-spinal system in the monkey (Macaca mulatta). The spinal pathways and preterminal distribution of degenerating fibers following discrete lesions. J. comp. Neurol. 123, 257-284. 29. Myers R. E., Sperry R. W. and McGurdy N. M. (1962) Neuronal mechanisms in visual guidance of limb movement. Arch. Neurol. 7, 195-202. 30. Nelson R. J. and Kaas J. H. (1981) Connections of the ventroposterior nucleus of the thalamus with the body surface representations in cortical areas 3b and 1 of the cynomolgus macaque (Macaca fascicularis). J. comp. Neurol. 199, 29-64. 31. Nelson R. J., Sur M., Fellman D. J. and Kaas J. H. (1980) Representations of the body surface in postcentral parietal cortex of Macaca fascicularis. J. comp. Neurol. 192, 611-643. 32. Savaki H. E., Kennedy C., Sokoloff L. and Mishkin M. (1993) Visually guided reaching with the forelimb contralateral to a "blind" hemisphere: a metabolic mapping study in monkeys. J. Neurosci. 13, 2772-2789. 33. Schwartz A. B., Kettner R. E. and Georgopoulos A. P. (1988) Primate motor cortex and free arm movements to visual targets in three-dimensional space. I. Relations between single cell discharge and direction of movement. J. Neurosci. 8, 2913-2927. 34. Sessle B. J. and Wiesendanger M. (1982) Structural and functional definition of the motor cortex in the monkey (Macaca fascicularis). J. Physiol. 323, 245~65. 35. Shanks M. F., Pearson R. C. A. and Powell T. P. S. (1985) The callosal connections of the primary somatic sensory cortex in the monkey. Brain Res. Rev. 9, 43-65. 36. Shanks M. F. and Powell T. P. S. (1981) An electron microscopy study of the termination of thalamocortical fibres in area 3b, 1 and 2 of the somatic sensory cortex in the monkey. Brain Res. 218, 35-47. 37. Sokoloff L., Reivich M., Kennedy C., Des Rosiers M. H., Patlak C. S., Pettigrew K. S., Sakurada O. and Shinohara M. (1977) The [~4C]-deoxyglucose method for the measurement of local cerebral glucose utilization: theory, procedure, and normal values in the conscious and anesthetized albino rat. J. Neurochem. 28, 879-916. 38. Tigges J., Nakagawa S. and Tigges M. (1979) Efferents of area 4 in a South American monkey (Saimiri). I. Terminations in the spinal cord. Brain Res. 171, 1-10. 39. Tokuno H. and Tanji J. (1993) Input organization of distal and proximal forelimb areas in the monkey primary motor cortex: a retrograde double labeling study. J. comp. Neurol. 333, 199-209. 40. Tommerdahl M., Favorov O. V., Whitsel B. L., Nakhle B. and Gonchar Y. A. (1993) Minicolumnar activation patterns in cat and monkey SI cortex. Cereb. Cortex 3, 399-411. 41. Vogt B. A. and Pandya D. N. (1977) Cortico-cortical connections of somatic sensory cortex (areas 3, 1 and 2) in the rhesus monkey. J. comp. Neurol. 177, 179-192. 42. Wong Y. C., Kwan H. C., MacKay W. A. and Murphy J. T. (1978) Spatial organization of precentral cortex in awake primates. I. Somatosensory inputs. J. Neurophysiol. 41, 1107 1119. 43. Woolsey C. N., Settlage P. H., Meyer D. R., Sencer W., Pinto Hamuy T. and Travis A. M. (1952) Patterns of localization in precentral and "supplementary" motor areas and their relation to the concept of a premotor area. Res. Pubis Ass. Res. nerv. ment. Dis. 30, 233~64. (Accepted 23 November 1995)