Distribution of cerebellar-induced responses in the cerebral cortex

EXPERIMENTAL

NEUROLOGY

Distribution

342-354 (1973)

of Cerebellar-Induced Cerebral Cortex

K. Department Kyoto

39,

SASAKI,

Y.

MATSUDA

AND

of Physiology, Institute for BraiN University,Kyoto and Department Dentistry,

Hiroshima Received

N.

in the

MIZUNO

Research, Faculty of Medicine, of Anatomy, School of Hiroshinaa, Japart

University, November

Responses

2,1972

Distribution of responses in the cerebral cortex elicited by stimulation of cerebellar nuclei was investigated in cats lightly anesthetized with Nembutal. Stimulation of the interpositus nucleusproducedmoremarkedresponses than that of the lateral nucleus but no distinguishable difference was noted between the localizations of responses in the cerebral cortex elicited by stimulating these nuclei. Medial nucleus stimulation set up little or no response in the cortex. Therefore, effects of stimulating the interpositus nucleus were mainly presented in this report. Cerebellar-evoked responses could be recorded from two regions in the cortex, frontal motor and parietal association areas; both were contralateral to the cerebellar nuclei stimulated. In the frontal cortex, the responses composed mainly of the deep thalamocortical (T-C) response were distributed in the exposed area of the anterior sigmoid gyrus, the deeply folded cruciate cortex, and a part of the exposed area of the posterior sigmoid gyrus. In the parietal cortex, the superficial T-C responses appearedin the middlesuprasylviancortex, a rostra1part of the lateral gyrus, and its extension to the mesial cortex.

INTRODUCTION of cerebellar nucleus stimulation appear not only in the frontal motor cortex as reported by many investigators (4) but also in the parietal suprasylvian gyrus in cats (16). Laminar field potential analysis in these Effects

regions

revealed

that

cerebellar-induced

responses

in the frontal

and

the

parietal cortex are different in nature, i.e., the responsesin the frontal car.tex are principally composed of deep thalamocortical (T-C) responsesand those in the parietal cortex consist purely of superficial T-C responses(16) (for deep and superficial T-C responses,seeRef. 15). Microelectrode studies in the thalamus showed that the responses in the frontal cortex are relayed by the ventral lateral (VL) nucleus (7, 10, 13, 19) while those 342 Copyright All rights

0 1973 by Academic Pres, Inc. of reproduction in any farm reserved.

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in the parietal cortex are mediated by the ventral anterior (VA) nucleus or its neighboring nuclei in the thalamus or both (16, 17). In this report, the distribution of responsesin the frontal and the parietal cortex induced by stimulatin g cerebellar nuclei, mainly the interpositus nucleus, will be dealt with in detail, as our previous papers were chiefly concerned with the nature of the frontal and the parietal responses (16) and with the thalamic relay mechanism of the responses (17). METHODS Cats were lightly anesthetized with intravenous administration of Nembutal (an initial dose of 20 mg/kg). The head of animal was fixed to a stereotaxic instrument. Craniotomy was performed to expose the frontal, parietal or mesial cortex for recording and to introduce stimulating electrodes in the cerebellum. In some experiments the ocular bulb was enucleated on one side and the orbital bone was cut away for the purpose of recording responsesfrom the orbitofrontal cortex. In order to record from the mesial cortex, the hemisphere contralateral to the recording side was aspirated with a suction ptmp (Fig. 1) . For stimulation of the cerehellar nuclei, concentric stainless steel electrodes, 0.8 mm in outer diameter and 0.5 mm in interpolar distance, were stereotaxically introduced into the medial, the interpositus and the lateral nuclei of the cerebellum contralateral to the recording side (Fig. 1, M, I and L). Scluare pulse current, 0.3-0.5 msec in duration, was applied at a frequency of 0.5-l/set for cerebellar nucleus stimulation. Glass micropipettes filled with 4 M-NaCl and with a d-c resistance of about 2 Mohm were used for depth recording in the cortex (Fig. 1, ME). Surface recording was made with a silver hall-tip electrode placed in the vicinity of microelectrode track (Fig. 1, SR) . The animals were immobilized with SFlaxedil (gallamine triethiodide) , and the respiration was controlled artificially. The respiratory movement was minimized by means of pneumothorax. The exposed surface of the cortex was covered with warm Ringer’s solution dropped continuously. After every experiment, the brain was fixed with 10 per cent formalin, and the sites of stimulation in the cerebellum were examined histologically. RESULTS Cerebellar-Ezloked Responses in the Pericrzrciate Cortices. Responsesinduced by stimulation of the cerebellar nuclei were recorded in the frontal lobe of the contralateral hemisphere, i.e., pericruciate and orbitofrontal cortices. Effects of medial nucleus stimulation were dubious in our experiments and will not be mentioned particularly (see Discussion). Stimulation of the interpositus nucleus usually elicited more prominent responsesthan

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MIZIJNO

FIG. 1. Diagrams illustrating experimental arrangements for cerebellar stimulation and cerebral recording. Concentric stimulating electrodes were stereotaxically introduced into the cerebellar nuclei (NUCL. CERL.), i.e., the medial (M), interpositus (I) and lateral (L) nuclei. Laminar field potential recording was performed with a glass microelectrode (ME) in the parietal, frontal or mesial cortices contralateral to the side of cerebellar stimulation. Potentials of the cortical surface were recorded with a silver ball-tip electrode (SR) placed in the vicinity of the microelectrode. SUPS : suprasylvian SU~CUS. LAT : lateral sulcus. CRU : cruciate sulcus. SPL : splenial sulcus.

of the lateral nucleus, but any marked difference was not noted between the cortical distributions of the responsesevoked by stimulating these two nuclei (see Discussion). Therefore, the responses evoked by interpositus stimulation will mainly be presented for the distribution of cerebellar-induced responsesin the cerebral cortex in this paper. As reported previously (8, 15), responsesrecorded with a gross surface electrode in the postcruciate cortex of the cat on thalamic stimulation often lead to a misinterpretation as to their sites of origin becauseof complexities of the gyral configuration in this area (6). Potentials thus recorded may merely represent activities in the underlying hidden cortex. The samesituation may hold for responseselicited around the cruciate sulcus by stimuthat

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FIG. 2. Field potentials generated in the depths of the cruciate cortex on stimulation of the cerebellar interpositus nucleus before (A) and after (B) ablation of the overlying postcruciate part. Experimental situations for the records A and B are illustrated in the inset diagramsA and B, respectively. Potentials were recorded with a microelectrode (M.E.) at depths indicated on the left side of each frame and with a gross electrodeplacedon the cortical surface (S.R.). Voltage calibrationof 1 mv is

applicableto all microelectroderecords.Time scaleof 10 msecfor all records.In this and following figures, records presented were obtained by superimposing several succeeding responses elicited at a frequency of OS-l/see. CRU : cruciate sulcus.

lation of the cerebellar nuclei. This was checked by using field potential analysis in the depths of the postcruciate cortex, and the interpretation of depth profiles was made on the basis of the definite pattern of laminar field potential distribution of the cerebellar-evoked responsesin the precruciate motor cortex (16). Figure 2 illustrates an example of laminar field potential analysis in the posterior sigmoid gyrus on interpositus stimulation. A microelectrode (M.E.) was introduced into the gyrus as shown in the inset diagram A and field potentials evoked by interpositus stimulation were recorded at every l-mm step in the track as exemplified in the records of column A. A gross electrode (S.R.) placed near to the microelectrode track on the posterior sigmoid gyrus picked up initial positive and later negative potentials as given in the bottom row of A, which are similar to the surface potential recorded from the anterior sigmoid gyrus on interpositus stimulation (‘Fig. 3 H-K). Microelectrode recording in the depths, however, revealed no actual response in the Ijosterior sigmoid gyrus, as there can be seell no definite dipole moment, Ijolarity reversal, in the superficial layer of

the gyrus (0 and 1 mm in A). True responses,signed by polarity reversal, are noted in 2-3 mm and 3-4 mm in A. Such depth profiles can be in-

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MIZUNO

FIG. 3. Field potentials in the depths of the per&Gate cortex elicited by stimulation of the interpositus nucleus. Records A-K were obtained at the corresponding points indicated by the same alphabetical symbols in the inset diagram, the depth from the cortical surface being denoted on the left side of each record in mm. Potentials re-

corded with a gross electrode placed on the surface are presented below the field potentials. Voltage calibration of 1 mv is applied to microelectrode records. Time scale of 10 msec for all records. LAT : lateral sulcus. CRU : crtlciate sulcus.

terpreted as due to responsesgenerated in upper and lower cortices facing each other in the deeply folded cruciate sulcus (15). The depth profiles also indicate that main events in the cruciate cortices are deep thalamocortical (T-C) responses, as the positivity at the cortical surface (3 mm, presumably in the cruciate sulcus) reversed to the negativity at the depths in both cortices facing each other (2 mm and 4 mm) ( 15). The interpretation mentioned above was supported by ablation experiments as ikstrated in the inset diagram B and the records in B column of Fig. 2. The cortical mass overlying the cruciate sulcus was removed by aspiration as in the diagram B, after field potentials in the depths had been recorded as shown in A. Depth recording of responseson cerebellar stimulation was thus performed in the hidden cortical region exposed, the cortex below the cruciate sulcus, and it revealed clearly deep T-C responsesin the cortex with corresponding surface potentials (S.R.) as presented in B. The potential recorded at a depth of 3 mm from the dorsal surface of the postcruciate cortex in Fig. 2A appears to correspond to that at 0 mm in B, which is compatibIe with the fact that the thickness of the removed cortex was, at the place recorded, about 3 mm.

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FIG. 4. Distribution of responses evoked by cerebellar nucleus stimulation in the hidden cruciate cortex. Results of two representative experiments are shown in A and B, respectively. The concealed gyri are schematically illustrated as the parts encircled by interrupted lines [see Hassler and Muhs-Clement (6)]. Relative size of responses is approximately signified with diameter of filled circles. Unresponsive cortical points are indicated by asterisks. CRU : cruciate sulcus. LAT : lateral sulcus.

In Fig. 3 are shown sample records of depth field potentials induced by interpositus stimulation at points indicated by alphabetical signs in the pericruciate cortices in the inset diagram. In the precruciate cortex, surface positive potentials reversed in sign at deep layers of the cortex (H-K in Fig. 3), and the depth profile of the surface positive (0 mm) and the deep negative (1.5 mm) component is comparable to that of the deep T-C response (15), as described in the preceding paper (16). The deep T-C response was followed by a small superficial T-C response seen as surface negativity and deep positivity. Surface recording made with a gross electrode at the points immediately caudal to the cruciate sulcus (D-G in Fig. 3) also exhibited a positive and following negative sequence of potentials so similar to that in the precruciate cortex. Depth recording in the postcruciate cortex, however, revealed that there was no recognizable response generated actually in the dorsal surface of the postcruciate cortex except in the rostrolaterally situated areas (F and G in Fig. 3). Tracks A-C were made further caudally. Potential distributions in the depths of the postcruciate cortex as shown in A-E in ,Fig. 3 are reasonably understood if active responsesare considered to be evoked in the underlying folded cortex around the deep cruciate sulcus (15). In fact, the generation of cerebellar-

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MIZUNO

A S.R.r&km= ” o”“*!?

FIG. 5. Depth field potentials evoked by stimulation of the interpositus nucleus and recorded in the mesial pericruciate cortex. Records in A and B were obtained above and below the cruciate sulcus, respectively, as shown in the inset diagrams.Presumed

tracks of the microelectrode(ME) are illustratedin the diagramof the frontally sectionedbrain. Distancefrom the cortical surfacealong the electrodetracks is indicated on the left side of each record in mm. S.R.: surface potentials recorded with a gross electrode (SR in the diagram) placed near to the point of microelectrode penetration.

Voltage calibrationof 1 mv is for the microelectroderecords; 10 msecscalefor all records. CRU : cruciate sulcus. SPL : splenial sulcus.

evoked responses, dipole moments, was confirmed by ablation studies as already presented in Fig. 2. Two representative casesof systematic explorations of cerebellar (interpositus) evoked responsesin the pericruciate cortex are schematically illustrated in Fig. 4, in which the hidden cortex is unfolded as the part encircled by interrupted lines (6). Amplitude of responsesrecorded at a depth of about 1.5 mm from the cortical surface and signified approximately by diameter of filled circles tends to become larger rostralwards and is obviously larger in the floor side (ventral lip) of the folded gyri, to which is contiguous the markedly responsive zone of the precruciate cortex. Al-

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mm 0 E

nucleus and recorded in FIG. 6. Respanses elicited by stimulatin g the interpositus the suprasylvian gyrus (A) and in the rostra1 part of the lateral gyms (B). The sites of recording are indicated by A and B in the inset diagram. The uppermost traces (S.R.) are surface potentials recorded with a gross electrode placed near the microelectrode tracks. Depth in the microelectrode tracks is given to the left in mm. Voltage calibration of 1 mv is applicable to all microelectrode records. 10 msec scale for all records. LAT : lateral sulcus. SUPS : suprasylvian sulcus.

most all parts of the postcruciate cortex exposed dorsally were confirmed to be unresponsive to cerebellar nucleus stimulation as indicated by asterisks in Fig. 4. In this gyms, active responses were recordable only rostrolateral region immediately caudal to the cruciate sulcus,

in the which

correspond to area 4y (6). Cerebellar-evoked responsesin the precruciate cortex were traced rostrally to the most rostra1 portion of the anterior sigmoid gyrus. Their distribution summarized in four experiments is plotted in Fig. 7A and I3 with filled circles, the diameter of which indicates approximately response amplitude measured at its maximum negativity in the cortical depths. The

3.50

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FIG. 7. The cortical distribution of responses elicited by stimulation bellar nuclei. A, B and C represent the dorsal, frontal and mesial view sphere respectively. The two types of responses are shown by filled and Diameter of the circles signifies relative amplitude of responses. See cruciate sulcus. LAT : lateral sulcus. SUPS : suprasylvian sulcus. COR: cus. SPL : splenial sulcus.

of the cereof the hemiopen circles. text. CRU: coronal sul-

most remarkable response was usually elicited in the region close to the lateral edge of the cruciate sulcus. Responsesbecame less prominent rostrally and ventrally, and active responsescould not be detected over the coronal sulcus. Exploration of responseswas also performed in the mesial pericruciate cortex. In Fig. 5A are exemplified field potentials recorded in the depths of the mesial pericruciate cortex dorsal to the cruciate sulcus, the presumed electrode track (A) being illustrated in the inset diagram representing the frontal section of brain. Responsesare recognizable only in deeply situated sites (at a depth of 5-9 mm in Fig. 5A), where the microelectrode was supposedto cross the cruciate sulcus in the depths. It is obvious that the gross electrode placed on the mesial surface of the cortex picked up responsesgenerated in remote hidden loci. On the other hand, responses were identified as active ones in the mesial pericruciate cortex ventral to the sulcus as shown in Fig. 5B. The initial surface-positive and the later surface-negative waves are in accordance with the deep and the superficial

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T-C response respectively in regard to the depth profiles (15). The distribution and magnitude of cerebellar-evoked responses in the mesial pericruciate cortex is summarized as in ,Fig. 7C, which shows no active response in the mesial cortex dorsal to the cruciate sulcus. Cerebellar-Evoked Responses ifa the Suprusyhiun and the Lateral Cyrus. It has been reported (16) that stimulation of the cerebellar nuclei (interpositus and lateral nuclei) evoked responses in the suprasylvian gyrus which differ in depth profiles of laminar field potentials from the responses elicited in the frontal pericruciate cortex. They have been confirmed to correspond to the superficial T-C response originally advocated for thalamocortical responses (15). In the present study, the occurrence of such responses in the suprasylvian gyrus was reassured. In addition, the response with the same pattern was found to be elicitable in the rostra1 part of the lateral gyrus. In Fig. 6 are presented specimen records of cerebellar-evoked responses in the suprasylvian gyrus (A) and in the rostra1 end of the lateral gyrus (B). In both A and B of Fig. 6, laminar potential profiles are characteristic of the superficial T-C response in that surface-negative waves are turned into deep-positivity at superficial cortical layers. Responses with the same depth profiles, though much smaller in amplitude, were also recorded on the mesial side of the cortex situated dorsally to the splenial sulcus and near to the rostra1 end of this sulcus. The cortical distribution of superficial T-C responses produced by interpositus stimulation summarized in numerous experiments is illustrated with open circles in A and C of Fig. 7, where the relative amplitude of responses is denoted approximately by their diameter. DISCUSSION Two types of cerebellar-evoked responses identified by laminar field potential analysis in the anterior sigmoid and the middle suprasylvian cortex respectively (16) were investigated in extensive areas of the cerebral hemisphere in the present study. The one type which consists principally of a deep thalamocortical (T-C) response is distributed in the exposed portion of the anterior sigmoid gyrus, the area of the pericruciate gyri hidden in the cruciate sulcus and a small part of the posterior sigmoid gyrus immediately caudal to the lateral part of the cruciate sulcus (Figs. 4 and 7). These areas belong to the cortical division characterized as motor in nature (6). It was confirmed that potentials recorded by a gross surface electrode in the most part of the posterior sigmoid gyrus, somatosensory area, were not due to active responses in the gyrus but merely reflection of the responses induced in the deeply folded hidden cruciate cortex. The responses in the frontal motor areas may be mediated by the projection path relayed in the ventral lateral (VL) nucleus of the thalamus (5, 7, 10, 13, 19).

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Rispal-Padel et al. ( 11) reported recently somewhat different topographical distributions of cerebellar-evoked responses in the frontal cortex due to the different cerebellar nuclei stimulated, and they showed the effect of medial (fastigial) nucleus stimulation in the frontal cortex. In the present study, no significant difference was recognized between the distributions of the responses evoked by stimulation of the interpositus and the lateral nucleus, though the responses evoked by the interpositus nucleus stimulation usually showed a larger amplitude than those elicited by the lateral nucleus stimulation. The responses were detectable in area 4 as well as in area 6 (6) on stimulation of both interpositus and lateral nucleus, although there was found a tendency to preponderance in area 4 (the lateral part of the anterior sigmoid gyrus). In some cases of interpositus and lateral nucleus stimulation, responses were relatively large in the medial part of the precruciate cortex and of the hidden cruciate cortex (presumably area 6 a/?), for instance as shown in Fig. 4B. No marked difference was noted between the distributions of responses induced by stimulation of the anterior and the posterior portion of the interpositus nucleus. Stimulating effects were generally more marked when an electrode was located in the anterior than the posterior portion of the nucleus. Such a comparison, however, would be difficult because an electrode introduced in the anterior portion can activate also efferent fibers arising from the posterior portion of the nucleus. Stimulation of the medial nucleus of the cerebellum showed little or no response in the cerebral cortex in this study. While a stimulating electrode introduced in the region between the medial and the interpositus nucleus could evoke responses in the cerebral cortex, an electrode placed in the medial nucleus, just above the nucleus or closely medial to the nucleus, did not set up any marked response in the cerebral cortex. Therefore, the cerebral cortical responses produced by a stimulating electrode placed between the medial and the interpositus nucleus were taken to be due to current spread to the interpositus nucleus. Stimulating electrodes attempted to be introduced stereotaxically in the medial nucleus were in fact frequently found by later histological checking to be located in the areas between the medial and the interpositus nucleus. Discrepancies between the results obtained in this study and those reported by Rispal-Padel et al (11) as for the stimulating effect of the medial nucleus might be in part attributable to different experimental conditions, e.g., the anesthetic used. Anatomical studies traced the cerebellar efferent projections from the medial nucleus to the thalamus (l-3, 18, ZO), and the topographical relations between the ventral lateral (VL) nucleus and the motor cortex were studied (12). There have been reported generalized influences of repetitive stimulation of the medial nucleus on activities of the cerebral cortex by a few investigators (4). It should be necessary to ex-

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amine further the effect of medial nucleus stimulation and the nature of cerebral cortical responses, if produced. Another type of the cerebellar-evoked responses in the cerebral cortex, superficial T-C responses, has been originally found in the suprasylvian gyrus (16). This type of responses was detected also in the dorsal and the mesial surface of the rostra1 part of the lateral gyrus (Fig. 7A and C) . The responses must be engendered through the thalamocortical projection system which conveys the superficial T-C response. Recently evidences have been presented for the projection, i.e., the neurons in and/or around the ventral anterior (VA) nucleus of the thalamus receive monosynaptic contacts from the cerebellar nuclei and they in turn project directly to the suprasylvian gyrus (17). It is conceivable that such superficial T-C projections are distributed in the middle suprasylvian gyrus as well as in the anterior part of the lateral gyrus and that they further extend to the part of the mesial cortex. Such a transversal band extending from the anterior part of the middle suprasylvian gyrus to the mesial cortex corresponds esactly to areas 5 and 7 or to the posterior integration cortex according to the cytoarchitectonic studies (6, 14). Recruiting responses (superficial T-C response) are elicited in these areas on repetitive (S-12/set) stimulation of certain thalamic nuclei, and it is recently verified that the thalamocortical neurons for the cerebellar-evoked superficial T-C response (17) also convey the recruiting responses in these cerebral cortical areas (Sasaki, Matsuda and Mizuno, in preparation). The general scheme of the cerebella-thalamo-cerebral projections is organized in such a way that a part of them reaches the frontal motor cortex and another to the parietal association cortex. There are found direct neuronal tracts from the parietal cortex to the pontine nuclei (9) which in turn send mossy fibers to the cerebellar cortex (Sasaki, Matsuda, Shimono and Mizuno, in preparation). The projection from the cerebellar nuclei to the parietal cortex must be concerned with the regulation of posture and movement in parallel to the cerebellar projection to the frontal motor cortex. Functional meanings of such a duality in the mode of the cerebellocerebral projections remain to be elucidated. REFERENCES 1. ANGAUT, P., and D. BOWSHER. 1970. Ascending projections of the medial cerebellar (fastigial) nucleus. An experimental study in the cat. Brain Res. 24: 46-68. 2. CARPENTER, M. B., G. M. BRITTIN, and J. PINES. 1958. Isolated lesions of the fastigial nuclei in the cat. J. Comb. Ncrwol. 109: 65-90. 3. COHEN, D., W. W. CHAMBER, and J. M. SPRAGUE. 1958. Experimental study of the efferent projections from the cerebellar nuclei to the brain stem of the cat. J. Conzp. Neztrol. 109: 233-259. Physiology and Pathology of the 4. Dow, R. S., and G. MORUZZI. 1958. “The Cerebellum.” University of Minnesota Press, Minneapolis.

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M., Y. LAMARRE, and J. P. CORDEAU. 1971. Neuronal discharges of the ventrolateral nucleus of the thalamus during sleep and wakefulness in the cat. II. Evoked activity. Exp. Brain lies. 12: 499-508. 6. HASSLER, R., and K. MUHS-CLEMENT. 1964. Architektonischer Aufbau des sensorimotorischen und parietalen Cortex der Katze. J. Hiwjorsch. 6: 377-420. 7. LAMARRE, Y., M. FILION, and J. P. CORDEAU. 1971. Neuronal discharges of the ventrolateral nucleus of the thalamus during sleep and wakefulness in the cat. I. Spontaneous activity. Exp. Brain Res. 12: 480-498. 8. MASTUDA, Y., K. SASAKI, and N. MIZUNO. 1972. Examination of responses evoked in the sensory cortex by thalamic stimulation. Jap. J. Physiol. 22: 651-666. 9. MIZUNO, N., K. MOCHIZUKI, C. AKIMOTO, R. MATSUSHIMA, and K. SASAKI. 1973. Projections from the parietal cortex to the brain stem nuclei in the cat, with special reference to the parietal cerebra-cerebellar system. J. Camp. Neural. 147 : 511-522. 10. PURPURA, D. P., T. L. FRIGYESI, J. G. MCMURTRY, and T. SCARFF. 1966. Synaptic mechanisms in thalamic regulation of cerebella-cortical projection activity, pp. 153-172. Ln “The Thalamus.” Columbia Univ. Press, New York. 11. RISPAL-PADEL, L., J. LATREILLE, and P. VANUXEW 1971. R&partition sur le cortex des projections des differents noyaux cerebelleux chez le Chat. C. R. Acad. Sci. (Paris) 272: 451-454. 12. RISPAL-PADEL, L., and J. MASSION. 1970. Relations between the ventrolateral nucleus and the motor cortex in the cat. Exp. Brailt Res. 10: 331339. 13. SAKATA, H., T. ISHIJIMA, and Y. TOYODA. 1966. Single unit studies on ventrolateral nucleus of the thalamus in cat: its relation to the cerebellum, motor cortex and basal ganglia. Jap. J. Physiol. 16: 42-60. 14. SANIDES, F., and J. HOFFMANN. 1969. Cyto- and myeloarchitecture of the visual cortex of the cat and of the surrounding integration cortices. J. Hirnforsch. 11: 79-104. 15. SASAKI, K., H. P. STAUNTON, and DIECKMANN. 1970. Characteristic features of augmenting and recruiting responses in the cerebral cortex. Exp. NezLroZ. 26: 369-392. 16. SASAKI, K., S. KAWAGUCHI, Y. MATSUDA, and N. MIZUNO. 1972. Electrophysiological studies on cerebella-cerebral projection in the cat. Exp. Brain Res. 16: 75-88. 17. SASAKI, K., Y. MATSUDA, S. KAWAGUCHI, and N. MIZUNO. 1972. On the cerebello-thalamo-cerebral pathway for the parietal cortex. Exp. Brain Res. 16: 89-103. 18. THOMAS, D. M., D. P. KAUFMAN, J. M. SPRAGUE, and W. W. CHAMBERS. 1956. Experimental studies of the vermal cerebellar projections in the brain stem of the cat. (Fastigiobulbar tract). J. Anat. (London) 90: 371-385. 19. TJNo, M., M. YOSHIDA, and I. HIROTA. 1970. The mode of cerebella-thalamic relay transmission investigated with intracellular recording from cells of the ventrolateral nucleus of cat’s thalamus. Exp. Brain. Res. 10: 121-139. 20. VOOGD, J. 1964. “The Cerebellum of the Cat. Structure and Fibre Connexions.” Doctoral Dissertation, Van Gorcum, Assen, 215 pp. 5. FILION,