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Projections from the medial nucleus of the inferior pulvinar complex to the middle temporal area of the visual cortex
0306-4522/80/1201-2219502.00/O
Neuroscience Vol. 5. pp.2219lo 2228 Pergamon PressLtd 1980.Printed inGreatBritain 8 IBRO
PROJECTIONS FROM THE MEDIAL NUCLEUS OF THE INFERIOR PULVINAR COMPLEX TO THE MIDDLE TEMPORAL AREA OF THE VISUAL CORTEX C.-S. LIN’~’ and J. H. KAAS’~” Departments of Psychology3 and Anatomy,’ Vanderbilt University, Nashville, Tennessee 37240, U.S.A. Attract-Medial, central, and posterior nuclei have been previously identi~ed within the inferior pulvinar complex of owl monkeys (LIN & KAAS, 1979). In the present experiments injections of C3H]-proline into the posterior thalamus, including the medial nucleus, produced densely labeled terminals in the middle temporal area of the visual cortex (ALLMAN & KAAS, 1971). Injections of the retrograde tracer, horseradish peroxidase, into the middle temporal area labeled most of the neurons in the medial nucleus and only occasional neurons in the central and posterior nuclei. The posterior nucleus appeared to project to the cortex rostra1 to the middle temporal area in the temporal lobe, and the central nucleus projects to the visual cortex caudal to the middle temporal area. We conclude that the middle temporal area is the major cortical target of the medial nucleus in the inferior pulvinar complex and that the central and posterior nuclei have other cortical targets. Thus, these findings support the view that the inferior pulvinar complex consists of three distinct nuclei, which should lead to further progress in understanding its connections and functions.
IN A PREVIOUSstudy, we used patterns of connections with other visual structures and architectonic characteristics to subdivide the inferior pulvinar complex of owl monkeys into three separate nuclei, the central inferior pulvinar (IPc), the medial inferior pulvinar (IPm), and the posterior inferior pulvinar (IPp) (LIN & KAAS, 1979). To briefly summarize, encapsulating fiber bands mark the boundaries of the three nuclei, and the IPm is further distinguished by a much greater packing density of neurons than the IPc and the IPp, While both the IPp and the IPc receive superior colliculus projections, the terminations in the IPp are much denser. The IPm appears to receive little or no superior colliculus input. Finally, visual cortical areas 17 and 18, the middle temporal area, the dorsomed~al area, the medial area and the posterior parietal area all project to the IPc and the IPm, but not to the IPp (visual areas are from ALLMAN & KAAS, 1976). The projections from the MT to the IPm are particularly dense. These three divisions of the inferior pulvinar have not been recognized in other monkeys. Other investigators have either included all three nuclei within the inferior pulvinar nucleus or sometimes included the IPp and occasionally the IPm in the posterior nucleus (see LIN & KAAS, 1979). The purpose of the present report is to present evidence that the principal and perhaps exclusive cortical target of one of the three nuclei, the IPm, is the middle temporal visual area (MT). In addition, ob-
t Present address: Department of Cell Biology, The University of Texas, Southwestern Medical School, Dallas, Texas 75235, U.S.A. Abbreviations: IPc, IPm, IPp, central, medial and posterior nuclei, respectively, of the inferior puivinar complex; MT, middle temporal area of the visual cortex.
servations are made on the cortical projections of the other two nuclei of the inferior pulvinar. EXPERIMENTAL
PROCEDURES
The projection patterns from the subdivisions of the inferior pulvinar complex were investigated in adult owl monkeys, Aotus r~~~~~g~rus, with autoradiographic methods after injections of 3H-proline into the thalamus or with histochemical procedures after injections of horseradish peroxidase (HRP) in visual cortex. The methods were basically those described previously (GRAHAM,LIN & KAAS, 1979; LIN & KAA$ 1979) as adapted from the autoradiography protocol of COWAN, GOTFLIEB,HENDRICKSON, PRICE& WOOLSEY(1972) or the HRP procedure of LAVAIL (1975). Owl monkeys were first anesthetized and then injections were made under aseptic conditions. Injections in the pulvinar complex were of tritiated proline (0.14.2 ~1 at 25-50 pCi/#l in saline) delivered in a 1 ~1 syringe mounted and stereotaxically placed. The injections were made gradually over 2&30 min and the syringe was left in place for an additional 20-30 min to reduce the contamination of overlying brain tissue. The monkeys survived from 3 to 7 days, were reanesthetized, and then perfused with saline followed by 10% formalin. The removed brains were stored in 30% sucrose in 10% formalin and later frozen and cut in 25 to 30&m frontal sections. Every tenth section or more was dipped in photographic emulsion, stored for 6-8 weeks, and processed for autoradio~raphy. Additional sections were stained with cresyl violet or hematoxylin for identifying thalamic nuclei and boundaries of cortical areas. norseradish peroxidase (HRP) (0.1-0.3~l of 30% Sigma type VI in saline) was injected with a 1~1 syringe over a period of 1@20min into the cortex of other monkeys which survived for 2 days and were perfused with saline followed by 8% formalin or by a mixture of 2% glutaraldehyde and 2% paraformaldehyde. The brains were stored overnight at 4°C in fixative with 30% sucrose, and then in a 0.1 M phosphate buffer containing 30% sucrose for approximately 24 h. The brains were frozen and cut in
2219
C.-S. LIN and J. H. lizi\>
2220
the frontal plane into %40 pm sections. reacted for HRP using diaminobenzidine according to the procedure of LAVAIL (1975), and stained with cresyl violet. Injection sites in the visual cortex were made by referring to surface features of the brain and were later verified by position relative to identified architectonic borders as described in
GRAHAME( (11.(1979). RESULTS The conclusion that the medial nucleus of the inferior pulvinar @Pm) projects densely to the middle temporal visual area (MT) (ALLMAN & KAAS, 1971), is based on findings in three monkeys with injections of13H]-proline that involve the IPm to varying extents, and seven monkeys with injections of HRP in the MT or other visual areas. The [3H]-proline injections are described first. Injections
of C3H] proline
Figure 1 illustrates the inferior pulvinar complex of an owl monkey with an injection site of [3H]-proline that filled most of the IPm (also see Plate 1B). Only a narrow caudal extreme and the dorsorostral margin of the nucleus were not densely labeled with silver grains. Much of the IPp and perhaps the dorsolateral margin of the medial geniculate complex were also labeled. The IPc was completely or almost completely avoided by the injection.
775
As a consequence of the Injection site +,~SII *I Fig. 1. dense label almost completely filled ‘1~ MT (Fig. 2). The sil\,er grains were not evenly Jlst!lhuiiL:. but they formed clumps or patches in the I~w:Y thrt-rl of layer III and tn layer IV (Plate IA!. \r,hic.i? WI-C separated by small region5 of sparse label. hdtlition:~l concentrations of silver grains were found ro,irai IO the MT in the temporal lobe. especially on rho hank\ of the superior tetnporal sulcus. No label abide background levels was found in area 17. area IX. 4rr Cmq of the visual areas bordering area 18. Comparisons with other cases illustrated in Figs. 3 11 indicate that the dense label almost filling the MT was a conscyucn~c of the portion of the injection in the IPm, whtle much of the label along the superior temporal sulcus of the temporal lobe was a result of the portion of the mlection in the IPp. A second injection site in the pulvinar complex i> illustrated in Fig. 3. This injection included the rostra1 half or more of the IPm, as well as a rostrodorsal portion of the IPc and part of the adjoining superior pulvinar (probably part of the central nucleus of the superior pulvinar as described by ~iRAHA’r1 C? d.. 1979). All except possibly the rostra1 extreme of’ the IPp was outside the injection site. The distribution of label in the cortex following rhe injection in Fig. 3 is shown in Fig. 4. The dorsal twothirds or more of the MT was filled with patches of
\
lmm
74-78
Id Pulvinar Ini.
FIG. 1. The injection site of [3H]-proline (shaded) in the inferior pulvinar complex in owl monkey 74 78 (also see Plate 1B). Frontal 30~ brain sections. The broken lines indicate axons coursing from the injection site toward the cortex. Central (IPc), medial (IPm) and posterior (IPp) nuclei of the inferior pulvinar complex are shown. Other abbreviations are: Cd, caudate nucleus; HP, hippocampus: LGN. lateral geniculate nucleus; SC, superior colliculus; SP, superior pulvinar.
2221
Inferior pulvinar projections
Owl Monkey 74 - 78
FIG. 2. The distribution of autoradiographic label in the middle temporal visual area (MT) and the temporal lobe after an injection of C3H)-prohne in the IPm and the 1Pp in owl monkey 7478. The patchy distribution of label in the MT is not shown. Arrows indicate hidden label. Areas 17, 18 and MT are delimited. silver grains. Other concentrations of label included layer IV and the lower third of layer III in parts of
Areas DL, 18, DM and DI. Silver grains were also found in the inner half of layer I in part of Area 17. The cortex rostra1 to the MT in the temporal lobe
had
no concentrations
of label
above
background
levels. These results, when compared with those of the first case, suggest that the dense label in the MT followed transport from the IPm, while the lack of label in the temporal lobe was a consequence of the injec-
IP,SP
Ini.
FIG. 3. The injection site in the [Pm, IPc and the superior pulvinar in owl monkey 7520. Conventions as in Fig. 1. NSC. S/l2-l
2222
c’.-s.
FIG. 4. The
LIN and J. H.
I(~44
cortical distribution of label after the injection shown in Fig. 3. DM. dorsomedial area; DL, dorsolateral area.
tion site almost completely sparing the IPp. The label in the other visual areas is attributed to the injection site involvement of the IPc and the superior pulvinar. The third thahunus injection (Fig. 5) was largely restricted to the superior pulvinar in the region of the lateral nucleus of the superior pulvinar (GRAHAM et al., 1979). As a consequence, dense label was observed
75-23 FIG. 5. An injection
in the cortex of the ventral temporal lobe (Fig. 6). The injection site also involved the dorsorostral margin of the 1Pm. the portion over the fiber band separating the rest of the inferior pulvinar from the superior pulvinar (LIN & KAAS. 19791. We interpret the sparse label in the caudal portion of the MT as a result of this slight encroachment on the IPm. Both the affec-
S.Pd. lnj.
site in the lateral superior pulvinar that encroaches on the 1Pm. WC. central of the inferior pulvinar. other conventions as in Fig. 1.
nucleus
Inferior pulvinar projections
2223
FIG. 6. Cortical label after the injection in Fig. 5.
ted part of the IPm (Lm & KAAS, 1979) and the labeled portion of the MT (ALLMAN & KAAS, 1971) represent central vision. Injections of horseradish peroxidase
The cases of HRP injections yielded consistent results. All injections in the MT produced retrogradely labeled neurons in the IPm, and if the injections were confined ot the MT, labeled neurons in the IPc and the IPp were either not found or were rare. An example of an injection of HRP that was restricted to the MT is shown in Fig. 7. In that case, the injection
site was centered in the MT and the brown reaction product was confined to the cortex immediately around the injection site within the MT. As a result, a zone of labeled cells was centered within the IPm. Labeled cells were not found in the IPp, the IPc, or other regions of the pulvinar complex. Labeled neurons in the IPm from a second similar case of an HRP injection confined to the MT are shown in Plate 1C. Altogether, injections of HRP were judged to be confined to the MT in four cases, and in each of these cases, a zone of labeled neurons was found only in the IPm.
HRP labeledzone in hf. Pd.
FIG. 7. An injection site of horseradish peroxidase in the middle temporal area of the visual cortex and the resulting zone of labeled cells (shaded) in the IPm. Conventions as in Fig. 1.
2224
C.-S. LIP; and J. H.
The results of a larger double injection of HRP filling nearly all of the MT, including some of the temporal lobe rostra1 to the MT and some of the dorsolateral area dorsal to the MT, are illustrated in Fig. 8. The zone of labeled cells occupied almost all of the IPm. Within this labeled zone. most cells contained obvious HRP granules. In a count of 163 neurons within a 0.48 mm square centered in the labeled zone, I12 neurons contained HRP (69”J. Practically all of the larger neurons were labeled while most of the unlabeled neurons were smaller. The mean size of the labeled cells in the sample was 145 pm’. while the mean size of the unlabeled cells was 9911m2. The labeled cells in the IPp, we believe. reflect the extension of the injection site into the visual cortex of the temporal lobe, while the involvement of the dorsolateral area could have labeled the limited zone of affected cells in the IPc. The cases included in Figs. l-8 indicate that most neurons in the IPm project to the MT and at least not strongly to any other region of the cortex. The second part of this conclusion is strengthened by the results of a final case where HRP was injected into a zone of cortex dorsal and medial to the MT and including the dorsomedial area, area 18, and area 17 (Fig. 9). While a zone of labeled cells was observed in the IPc, the IPm was free of labeled cells.
DISCUSSION The inferior pulvinar complex of owl monkeys has been divided into three nuclei with different input patterns and architectonic features, the central (IPc), the medial (IPm), and the posterior (IPp) nuclei of the inferior pulvinar (LIN & KAAS, 1979). The major con-
KAAS
I
-_
FIG. 8. The zone of labeled cells in the pulvinar complex after injections of horseradish peroxidase into the middle temporal area of the visual cortex. The injection site abo included cortex medial and rostra1 to the MT.
elusions of the present study are summarized in Fig. 10. The majority of neurons in the IPm project to the middle temporal visual area (MT) (ALLMAN & KAAS, 1971) while the IPp projects to the cortex rostral to the MT in the temporal lobe and the IPc projects to the cortex caudal to the MT in the occipital lobe. While the projections of the IPp and the IPc
HRP labeled zone in hf. Pul. FIG.9. The zone of dark brown reaction striate
cortex
and
the resulting
product after horseradish peroxidase zone of labeled cells in the central nucleus complex in owl monkey 7430.
injections in the extraof the inferior pulvinar
PLATE 1. (A) Darkfield photomicrograph of silver grain concentrations after the [‘Hlproline injection shown in Fig. 1. Notice the unewzn distribution of label. Large arrows mark the borders of the MT; small arrows point to the inner margin of cortical layer IV. Bar = 2 mm. (B) The injection site of [3H]-proline in owl monkey 74-78 [see Figs 1 and 2). Conventions as in previous Figures. Bar = 1 mm. (C) Darkfield photomicrograph of neurons labeled with horseradish peroxidase in medial nucleus of the inferior pulvinar complex. Owl monkey 7333. Bar = 400 p.
2221
Inferior pulvinar projections
Y sup.c.
\
Retina
FIG. 10. Cortical projections of the inferior pulvinar complex. The IPm projects to the MT, the IPp to the visual cortex rostra1 to the MT (the subdivisions are uncertain), and the IPc to the visual cortex caudal to the MT. The dashed line to VI indicates projections terminating in layer I. Superior colliculus projections are from Ln-4 &
KAAS(1979).
will have to be defined more precisely, the evidence for different cortical targets of the three nuclei of the inferior pulvinar complex supports the proposed subdivision. Subdividing the inferior pulvinar complex should lead to progress in understanding its connections and functions. Certainly, descriptions of the projections of the inferior pulvinar in primates have been conflicting and confusing, and this is a result, we think, of not distinguishing between the different projection patterns of the nuclei of the inferior pulvinar. For example, of the earlier investigations using the retrograde degeneration method, LE GROS CLARK & NORTHFIELD(1937) concluded that the inferior pulvinar projects to the prestriate cortex, and WALKER (1938) argued that it projects to the temporo-occipital regions. CHOW (1950) later noted that degenerative changes take place in the inferior pulvinar after either prestriate or temporo-occipital lesions. More recently, autoradiographic and histochemical tracers have been used to demonstrate projections from the inferior pulvinar to the prestriate cortex (TROJANOWSKI & JACOBSON,1976; WONG-RILEY,1977; BENEVENTO 8~ REZAK, 1976; GLENDENNING, HALL, DIAMOND& HALL, 1975;
REZAK & BENEVENTO,1979; WINFIELD, GATTER & POWELL,1975), the temporo-occipital cortex (TROJANOWSKI8~ JACOBSON, 1975; GLENDENNING et al., 1975; LIN, WAGOR& KAAS, 1974), and area 17 (OGREN & HENDRICKSON,1976; 1977;. REZAK & BENEVENTO, 1979; BENEVENTO& REZAK, 1975; BENEVENTO& REZAK, 1976). We suggest that IPp and IPm are the nuclei of the inferior pulvinar that project to the temporo-occipital cortex in the above studies, and more specifically, that IPm projects to MT and IPp projects to the cortex rostra1 to the MT in the temporal lobe. In addition, it is likely to be the IPc that accounts for terminations in the striate and the prestriate cortex. In support of these suggestions, TROJANOWSKI& JACOBSON (1975) noted that caudal and medial parts of the inferior pulvinar in squirrel monkeys project to the superior temporal gyrus just rostra1 to the MT (see SPATZ, 1975 for the location of the MT). The labeled portions of the inferior pulvinar appear to include the IPp and perhaps part of the IPm. In marmosets, SPATZ (1975) found that injections of HRP into MT-labeled neurons in the ‘posterior nucleus’, which appears to be the region that we term the IPm. The large proportional size of the IPc, 70% of the inferior pulvinar complex in owl monkeys and possibly even more in other monkeys, would account for the frequency with which IPc projections have been ascribed to the inferior pulvinar as a whole. Our material strongly suggests that it is only IPc and not the rest of the inferior pulvinar that projects to layers III and IV of the prestriate cortex and layer I of the striate cortex in monkeys. In addition to providing evidence that separate nuclei in the inferior pulvinar complex project to different regions of the cortex, the observation was made that pulvinar terminations in the MT and the parastriate cortex are patchy and discontinuous. The patchy distribution of pulvinar input to the parastriate cortex has been noted and discussed by other investigators (CURCIO & HARTING, 1978; WONGRILEY, 1979; REZAK & BENEVENTO, 1977; OGREN & HENDRICKSON, 1977), but
they
have
not
been
de-
scribed before
for thalamic input to the MT. Patchy termination fields for cortical projections from one visual area to another have been commonly described (see WELLER & KAAS. 1980 for review), and area 17 terminations in the MT of owl monkeys are also discontinuous (C.-S. LIN & J. H. KAAS, unpublished observations; MONTERO,1980). It is not known if the two types of patchy input to the MT are in or out of register, which could be two interesting possibilities. At present, the functional significance of the uneven input to the cortex from the pulvinar is unknown. Acknowledgement-This study was supported by NIH grant EY-02686.
2228
C.-S. LIK and J. H. KAAS REFERENCES
ALLMANJ. M. & KAASJ. H. (1971) A representation of the visual field in the caudal third of the middle titmpclr;t! : j II’+ :I: the owl monkey (Aotus criviryacus). Brain Res. 31, 85-105. ALLMANJ. M. & KAASJ. H. (1975) The dorsomedial cortical visual area: A third tier area in the occrprtal lobe d $ilt‘ 1~ I monkey (Aotus rricirgatus).Brain Res. 100, 473487. ALLMANJ. M. & KAASJ. H. (1976) Representation of the visual field on the medial wall of occipital-parirtal corree II*the owl monkey. Scienre, N.Y. 191, 572-575. BENEVENTO L. A. & REZAKM. (1975) Extrageniculate projections to layers VI and I of striate cortex (Area 1’; in :hc rhesus monkey (Macuco ~~~urtQ), Bruin Res. 96, 51.-55. BENEVENM) L. A. & REZAKM. (1976) The cortical projections of the inferior pulvinar and adjacent lateral putvinar in the rhesus monkey (Macacu mulatta): An autoradiographic study. Brain Res. 108, l-24. CHOW K. L. (1950) A retrograde cell degeneration study of the cortical projection field of the puivinar in the monkey. J camp. Neural 93, 3 13--340. COWANW. M., GOTTLIEBD. 1.. HENDRICKSON A. E., PRICEJ. L. & WWLSEYT. A. (1972) The autoradiographic demonstration of axonal connections in the central nervous system. Brain Res. 37, 21-51. CUR~IOC. A. & HARTINGJ. K. (1978) Organization of pulvinar afferents to Area 18 in the squirrel monkey: evidence for stripes. Brain Res. 143, 155- 161 GLENDENNING K. K., HALL J. A., DIAMOND1. T. & HALL W. C. (1975) The pulvinar nucleus of G&go uenegtrlcr~si.~I camp. Neural. 161, 419-458. GRAHAMJ., LIN C.-S. & KAASJ. H. (1979) Subcortical projections of six visual cortical areas in the owl monkey. ;torit\ trizlirgatus. .I. camp. Neural. 187, 5.57-580.
LAVAII.J. H. (1975) Retrograde cell degeneration and retrograde transport techniques. In The Use qf Axonal ‘rranspf~r~ for Studies of Neuronai Connectivity (eds COWAN W, M. & CU~NODM.), pp. 217-248. Elsevier, Amsterdam. LE GR~S CLARKW. E. R: NORTHFIELD W. C. (1937) The cortical projection of the pulvinar in the macaque monkey Brain Res. 60, 126-192. LIN C.-S. & KAASJ. H. (1979) The inferior pulvinar complex in owl monkeys: Architectonic subdivisions and patterns of input from the superior colliculus and subdivisions of visual cortex. J. camp. Neural. 187, 655.-678. LIN C.-S., WAGORE. & KAASJ. H. (1974) Projections from the pulvinar to the middle temporal visual area (MT) in the owl monkey, Aotus triuirgafus. Brain Res. 76, 145-149. MONERO V. M. (1980) Patterns of connections from the striate cortex to cortical visual areas in superior temporal sulcus of macaque and middle temporal gyrus of owl monkey. J. camp. Neuroi. 189,45-59. OGRENM. P. & HEN~RICK~N A. E. (1976) Pathways between striate cortex and subcortical regions in .&facuca ~~~~~~z~r~f and Suimiri sc~ureus: evidence for a reciprocal pulvinar connection. Expl. Neurot 53, 7~8~. OGRENM. P. & HENDRICKSON A. E. (1977) The distribution of pulvinar terminals in visual areas 17 and 18 of the monkey. Bruin Res. 137, 343--350. REZAK M. & BENEVENTO L. A. (1977) A redefinition of pulvinar subdivisions in the macaque monkey: Evidence for three distinct subregions within classically defined lateral ptilvinar. Neuroscience Abs 3, 574. REZAK M. & BENEVENTO L. A. (1979) A comparison of the organization of the projections of the lateral geniculate nucleus. the inferior pulvinar and adjacent lateral pulvinar to primary visual cortex (Area 17) in the macaque monkey. Brain Res. 167, 1940. SPATZ W. B. (1975) Thalamic and other subcortical projections to area MT (visual area of superior temporal sulcus) in the marmoset Callifhrix jacchus. Brain Res. 99, 129-134. TROJANOWSKI J. Q. & JACOBSON S. (1975) A combined horseradish ~roxidase-autoradiographic investigation of reciprocal connections between superior temporal gyrus and pulvinar in squirrel monkey. Bruin Res. 85, 347-353.
Trojanowski J. Q. & Jacobson S. (1976) Area1 and laminar distribution of some pulvinar cortical efferents in rhesus monkey. J. camp. Neural. 169, 371-392. WALKERA. E. (1938) The Primate Thaiamus. University of Chicago Press. WELLER,R. E. & KAAS, J. H. (1980) Cortical and subcortical connections of visual cortex in primates. In Multipk Cortictil Somatic Sensory-Motor, Visual and ,4uditory Areas and their Connections (ed. Woolsey, C. N.). Humana Press. Clifton, New Jersey. In Press. WINFIELDD. A., GATTERK. L. & POWELLT. P. S. (1975) Cerrtain connections of the visual cortex of the monkey shown by the use of horseradish peroxidase. Bruin Res. 92, 456-461. WONG-RILEYM. T. T. (1977) Connections between the pulvinar nucleus and the prestriate cortex in the squirrel monkey as revealed by peroxidase his&chemistry and autoradiography. Brain Res. 134, 249-267. (Accepted 3 July 1980)
Neuroscience Vol. 5. pp.2219lo 2228 Pergamon PressLtd 1980.Printed inGreatBritain 8 IBRO
PROJECTIONS FROM THE MEDIAL NUCLEUS OF THE INFERIOR PULVINAR COMPLEX TO THE MIDDLE TEMPORAL AREA OF THE VISUAL CORTEX C.-S. LIN’~’ and J. H. KAAS’~” Departments of Psychology3 and Anatomy,’ Vanderbilt University, Nashville, Tennessee 37240, U.S.A. Attract-Medial, central, and posterior nuclei have been previously identi~ed within the inferior pulvinar complex of owl monkeys (LIN & KAAS, 1979). In the present experiments injections of C3H]-proline into the posterior thalamus, including the medial nucleus, produced densely labeled terminals in the middle temporal area of the visual cortex (ALLMAN & KAAS, 1971). Injections of the retrograde tracer, horseradish peroxidase, into the middle temporal area labeled most of the neurons in the medial nucleus and only occasional neurons in the central and posterior nuclei. The posterior nucleus appeared to project to the cortex rostra1 to the middle temporal area in the temporal lobe, and the central nucleus projects to the visual cortex caudal to the middle temporal area. We conclude that the middle temporal area is the major cortical target of the medial nucleus in the inferior pulvinar complex and that the central and posterior nuclei have other cortical targets. Thus, these findings support the view that the inferior pulvinar complex consists of three distinct nuclei, which should lead to further progress in understanding its connections and functions.
IN A PREVIOUSstudy, we used patterns of connections with other visual structures and architectonic characteristics to subdivide the inferior pulvinar complex of owl monkeys into three separate nuclei, the central inferior pulvinar (IPc), the medial inferior pulvinar (IPm), and the posterior inferior pulvinar (IPp) (LIN & KAAS, 1979). To briefly summarize, encapsulating fiber bands mark the boundaries of the three nuclei, and the IPm is further distinguished by a much greater packing density of neurons than the IPc and the IPp, While both the IPp and the IPc receive superior colliculus projections, the terminations in the IPp are much denser. The IPm appears to receive little or no superior colliculus input. Finally, visual cortical areas 17 and 18, the middle temporal area, the dorsomed~al area, the medial area and the posterior parietal area all project to the IPc and the IPm, but not to the IPp (visual areas are from ALLMAN & KAAS, 1976). The projections from the MT to the IPm are particularly dense. These three divisions of the inferior pulvinar have not been recognized in other monkeys. Other investigators have either included all three nuclei within the inferior pulvinar nucleus or sometimes included the IPp and occasionally the IPm in the posterior nucleus (see LIN & KAAS, 1979). The purpose of the present report is to present evidence that the principal and perhaps exclusive cortical target of one of the three nuclei, the IPm, is the middle temporal visual area (MT). In addition, ob-
t Present address: Department of Cell Biology, The University of Texas, Southwestern Medical School, Dallas, Texas 75235, U.S.A. Abbreviations: IPc, IPm, IPp, central, medial and posterior nuclei, respectively, of the inferior puivinar complex; MT, middle temporal area of the visual cortex.
servations are made on the cortical projections of the other two nuclei of the inferior pulvinar. EXPERIMENTAL
PROCEDURES
The projection patterns from the subdivisions of the inferior pulvinar complex were investigated in adult owl monkeys, Aotus r~~~~~g~rus, with autoradiographic methods after injections of 3H-proline into the thalamus or with histochemical procedures after injections of horseradish peroxidase (HRP) in visual cortex. The methods were basically those described previously (GRAHAM,LIN & KAAS, 1979; LIN & KAA$ 1979) as adapted from the autoradiography protocol of COWAN, GOTFLIEB,HENDRICKSON, PRICE& WOOLSEY(1972) or the HRP procedure of LAVAIL (1975). Owl monkeys were first anesthetized and then injections were made under aseptic conditions. Injections in the pulvinar complex were of tritiated proline (0.14.2 ~1 at 25-50 pCi/#l in saline) delivered in a 1 ~1 syringe mounted and stereotaxically placed. The injections were made gradually over 2&30 min and the syringe was left in place for an additional 20-30 min to reduce the contamination of overlying brain tissue. The monkeys survived from 3 to 7 days, were reanesthetized, and then perfused with saline followed by 10% formalin. The removed brains were stored in 30% sucrose in 10% formalin and later frozen and cut in 25 to 30&m frontal sections. Every tenth section or more was dipped in photographic emulsion, stored for 6-8 weeks, and processed for autoradio~raphy. Additional sections were stained with cresyl violet or hematoxylin for identifying thalamic nuclei and boundaries of cortical areas. norseradish peroxidase (HRP) (0.1-0.3~l of 30% Sigma type VI in saline) was injected with a 1~1 syringe over a period of 1@20min into the cortex of other monkeys which survived for 2 days and were perfused with saline followed by 8% formalin or by a mixture of 2% glutaraldehyde and 2% paraformaldehyde. The brains were stored overnight at 4°C in fixative with 30% sucrose, and then in a 0.1 M phosphate buffer containing 30% sucrose for approximately 24 h. The brains were frozen and cut in
2219
C.-S. LIN and J. H. lizi\>
2220
the frontal plane into %40 pm sections. reacted for HRP using diaminobenzidine according to the procedure of LAVAIL (1975), and stained with cresyl violet. Injection sites in the visual cortex were made by referring to surface features of the brain and were later verified by position relative to identified architectonic borders as described in
GRAHAME( (11.(1979). RESULTS The conclusion that the medial nucleus of the inferior pulvinar @Pm) projects densely to the middle temporal visual area (MT) (ALLMAN & KAAS, 1971), is based on findings in three monkeys with injections of13H]-proline that involve the IPm to varying extents, and seven monkeys with injections of HRP in the MT or other visual areas. The [3H]-proline injections are described first. Injections
of C3H] proline
Figure 1 illustrates the inferior pulvinar complex of an owl monkey with an injection site of [3H]-proline that filled most of the IPm (also see Plate 1B). Only a narrow caudal extreme and the dorsorostral margin of the nucleus were not densely labeled with silver grains. Much of the IPp and perhaps the dorsolateral margin of the medial geniculate complex were also labeled. The IPc was completely or almost completely avoided by the injection.
775
As a consequence of the Injection site +,~SII *I Fig. 1. dense label almost completely filled ‘1~ MT (Fig. 2). The sil\,er grains were not evenly Jlst!lhuiiL:. but they formed clumps or patches in the I~w:Y thrt-rl of layer III and tn layer IV (Plate IA!. \r,hic.i? WI-C separated by small region5 of sparse label. hdtlition:~l concentrations of silver grains were found ro,irai IO the MT in the temporal lobe. especially on rho hank\ of the superior tetnporal sulcus. No label abide background levels was found in area 17. area IX. 4rr Cmq of the visual areas bordering area 18. Comparisons with other cases illustrated in Figs. 3 11 indicate that the dense label almost filling the MT was a conscyucn~c of the portion of the injection in the IPm, whtle much of the label along the superior temporal sulcus of the temporal lobe was a result of the portion of the mlection in the IPp. A second injection site in the pulvinar complex i> illustrated in Fig. 3. This injection included the rostra1 half or more of the IPm, as well as a rostrodorsal portion of the IPc and part of the adjoining superior pulvinar (probably part of the central nucleus of the superior pulvinar as described by ~iRAHA’r1 C? d.. 1979). All except possibly the rostra1 extreme of’ the IPp was outside the injection site. The distribution of label in the cortex following rhe injection in Fig. 3 is shown in Fig. 4. The dorsal twothirds or more of the MT was filled with patches of
\
lmm
74-78
Id Pulvinar Ini.
FIG. 1. The injection site of [3H]-proline (shaded) in the inferior pulvinar complex in owl monkey 74 78 (also see Plate 1B). Frontal 30~ brain sections. The broken lines indicate axons coursing from the injection site toward the cortex. Central (IPc), medial (IPm) and posterior (IPp) nuclei of the inferior pulvinar complex are shown. Other abbreviations are: Cd, caudate nucleus; HP, hippocampus: LGN. lateral geniculate nucleus; SC, superior colliculus; SP, superior pulvinar.
2221
Inferior pulvinar projections
Owl Monkey 74 - 78
FIG. 2. The distribution of autoradiographic label in the middle temporal visual area (MT) and the temporal lobe after an injection of C3H)-prohne in the IPm and the 1Pp in owl monkey 7478. The patchy distribution of label in the MT is not shown. Arrows indicate hidden label. Areas 17, 18 and MT are delimited. silver grains. Other concentrations of label included layer IV and the lower third of layer III in parts of
Areas DL, 18, DM and DI. Silver grains were also found in the inner half of layer I in part of Area 17. The cortex rostra1 to the MT in the temporal lobe
had
no concentrations
of label
above
background
levels. These results, when compared with those of the first case, suggest that the dense label in the MT followed transport from the IPm, while the lack of label in the temporal lobe was a consequence of the injec-
IP,SP
Ini.
FIG. 3. The injection site in the [Pm, IPc and the superior pulvinar in owl monkey 7520. Conventions as in Fig. 1. NSC. S/l2-l
2222
c’.-s.
FIG. 4. The
LIN and J. H.
I(~44
cortical distribution of label after the injection shown in Fig. 3. DM. dorsomedial area; DL, dorsolateral area.
tion site almost completely sparing the IPp. The label in the other visual areas is attributed to the injection site involvement of the IPc and the superior pulvinar. The third thahunus injection (Fig. 5) was largely restricted to the superior pulvinar in the region of the lateral nucleus of the superior pulvinar (GRAHAM et al., 1979). As a consequence, dense label was observed
75-23 FIG. 5. An injection
in the cortex of the ventral temporal lobe (Fig. 6). The injection site also involved the dorsorostral margin of the 1Pm. the portion over the fiber band separating the rest of the inferior pulvinar from the superior pulvinar (LIN & KAAS. 19791. We interpret the sparse label in the caudal portion of the MT as a result of this slight encroachment on the IPm. Both the affec-
S.Pd. lnj.
site in the lateral superior pulvinar that encroaches on the 1Pm. WC. central of the inferior pulvinar. other conventions as in Fig. 1.
nucleus
Inferior pulvinar projections
2223
FIG. 6. Cortical label after the injection in Fig. 5.
ted part of the IPm (Lm & KAAS, 1979) and the labeled portion of the MT (ALLMAN & KAAS, 1971) represent central vision. Injections of horseradish peroxidase
The cases of HRP injections yielded consistent results. All injections in the MT produced retrogradely labeled neurons in the IPm, and if the injections were confined ot the MT, labeled neurons in the IPc and the IPp were either not found or were rare. An example of an injection of HRP that was restricted to the MT is shown in Fig. 7. In that case, the injection
site was centered in the MT and the brown reaction product was confined to the cortex immediately around the injection site within the MT. As a result, a zone of labeled cells was centered within the IPm. Labeled cells were not found in the IPp, the IPc, or other regions of the pulvinar complex. Labeled neurons in the IPm from a second similar case of an HRP injection confined to the MT are shown in Plate 1C. Altogether, injections of HRP were judged to be confined to the MT in four cases, and in each of these cases, a zone of labeled neurons was found only in the IPm.
HRP labeledzone in hf. Pd.
FIG. 7. An injection site of horseradish peroxidase in the middle temporal area of the visual cortex and the resulting zone of labeled cells (shaded) in the IPm. Conventions as in Fig. 1.
2224
C.-S. LIP; and J. H.
The results of a larger double injection of HRP filling nearly all of the MT, including some of the temporal lobe rostra1 to the MT and some of the dorsolateral area dorsal to the MT, are illustrated in Fig. 8. The zone of labeled cells occupied almost all of the IPm. Within this labeled zone. most cells contained obvious HRP granules. In a count of 163 neurons within a 0.48 mm square centered in the labeled zone, I12 neurons contained HRP (69”J. Practically all of the larger neurons were labeled while most of the unlabeled neurons were smaller. The mean size of the labeled cells in the sample was 145 pm’. while the mean size of the unlabeled cells was 9911m2. The labeled cells in the IPp, we believe. reflect the extension of the injection site into the visual cortex of the temporal lobe, while the involvement of the dorsolateral area could have labeled the limited zone of affected cells in the IPc. The cases included in Figs. l-8 indicate that most neurons in the IPm project to the MT and at least not strongly to any other region of the cortex. The second part of this conclusion is strengthened by the results of a final case where HRP was injected into a zone of cortex dorsal and medial to the MT and including the dorsomedial area, area 18, and area 17 (Fig. 9). While a zone of labeled cells was observed in the IPc, the IPm was free of labeled cells.
DISCUSSION The inferior pulvinar complex of owl monkeys has been divided into three nuclei with different input patterns and architectonic features, the central (IPc), the medial (IPm), and the posterior (IPp) nuclei of the inferior pulvinar (LIN & KAAS, 1979). The major con-
KAAS
I
-_
FIG. 8. The zone of labeled cells in the pulvinar complex after injections of horseradish peroxidase into the middle temporal area of the visual cortex. The injection site abo included cortex medial and rostra1 to the MT.
elusions of the present study are summarized in Fig. 10. The majority of neurons in the IPm project to the middle temporal visual area (MT) (ALLMAN & KAAS, 1971) while the IPp projects to the cortex rostral to the MT in the temporal lobe and the IPc projects to the cortex caudal to the MT in the occipital lobe. While the projections of the IPp and the IPc
HRP labeled zone in hf. Pul. FIG.9. The zone of dark brown reaction striate
cortex
and
the resulting
product after horseradish peroxidase zone of labeled cells in the central nucleus complex in owl monkey 7430.
injections in the extraof the inferior pulvinar
PLATE 1. (A) Darkfield photomicrograph of silver grain concentrations after the [‘Hlproline injection shown in Fig. 1. Notice the unewzn distribution of label. Large arrows mark the borders of the MT; small arrows point to the inner margin of cortical layer IV. Bar = 2 mm. (B) The injection site of [3H]-proline in owl monkey 74-78 [see Figs 1 and 2). Conventions as in previous Figures. Bar = 1 mm. (C) Darkfield photomicrograph of neurons labeled with horseradish peroxidase in medial nucleus of the inferior pulvinar complex. Owl monkey 7333. Bar = 400 p.
2221
Inferior pulvinar projections
Y sup.c.
\
Retina
FIG. 10. Cortical projections of the inferior pulvinar complex. The IPm projects to the MT, the IPp to the visual cortex rostra1 to the MT (the subdivisions are uncertain), and the IPc to the visual cortex caudal to the MT. The dashed line to VI indicates projections terminating in layer I. Superior colliculus projections are from Ln-4 &
KAAS(1979).
will have to be defined more precisely, the evidence for different cortical targets of the three nuclei of the inferior pulvinar complex supports the proposed subdivision. Subdividing the inferior pulvinar complex should lead to progress in understanding its connections and functions. Certainly, descriptions of the projections of the inferior pulvinar in primates have been conflicting and confusing, and this is a result, we think, of not distinguishing between the different projection patterns of the nuclei of the inferior pulvinar. For example, of the earlier investigations using the retrograde degeneration method, LE GROS CLARK & NORTHFIELD(1937) concluded that the inferior pulvinar projects to the prestriate cortex, and WALKER (1938) argued that it projects to the temporo-occipital regions. CHOW (1950) later noted that degenerative changes take place in the inferior pulvinar after either prestriate or temporo-occipital lesions. More recently, autoradiographic and histochemical tracers have been used to demonstrate projections from the inferior pulvinar to the prestriate cortex (TROJANOWSKI & JACOBSON,1976; WONG-RILEY,1977; BENEVENTO 8~ REZAK, 1976; GLENDENNING, HALL, DIAMOND& HALL, 1975;
REZAK & BENEVENTO,1979; WINFIELD, GATTER & POWELL,1975), the temporo-occipital cortex (TROJANOWSKI8~ JACOBSON, 1975; GLENDENNING et al., 1975; LIN, WAGOR& KAAS, 1974), and area 17 (OGREN & HENDRICKSON,1976; 1977;. REZAK & BENEVENTO, 1979; BENEVENTO& REZAK, 1975; BENEVENTO& REZAK, 1976). We suggest that IPp and IPm are the nuclei of the inferior pulvinar that project to the temporo-occipital cortex in the above studies, and more specifically, that IPm projects to MT and IPp projects to the cortex rostra1 to the MT in the temporal lobe. In addition, it is likely to be the IPc that accounts for terminations in the striate and the prestriate cortex. In support of these suggestions, TROJANOWSKI& JACOBSON (1975) noted that caudal and medial parts of the inferior pulvinar in squirrel monkeys project to the superior temporal gyrus just rostra1 to the MT (see SPATZ, 1975 for the location of the MT). The labeled portions of the inferior pulvinar appear to include the IPp and perhaps part of the IPm. In marmosets, SPATZ (1975) found that injections of HRP into MT-labeled neurons in the ‘posterior nucleus’, which appears to be the region that we term the IPm. The large proportional size of the IPc, 70% of the inferior pulvinar complex in owl monkeys and possibly even more in other monkeys, would account for the frequency with which IPc projections have been ascribed to the inferior pulvinar as a whole. Our material strongly suggests that it is only IPc and not the rest of the inferior pulvinar that projects to layers III and IV of the prestriate cortex and layer I of the striate cortex in monkeys. In addition to providing evidence that separate nuclei in the inferior pulvinar complex project to different regions of the cortex, the observation was made that pulvinar terminations in the MT and the parastriate cortex are patchy and discontinuous. The patchy distribution of pulvinar input to the parastriate cortex has been noted and discussed by other investigators (CURCIO & HARTING, 1978; WONGRILEY, 1979; REZAK & BENEVENTO, 1977; OGREN & HENDRICKSON, 1977), but
they
have
not
been
de-
scribed before
for thalamic input to the MT. Patchy termination fields for cortical projections from one visual area to another have been commonly described (see WELLER & KAAS. 1980 for review), and area 17 terminations in the MT of owl monkeys are also discontinuous (C.-S. LIN & J. H. KAAS, unpublished observations; MONTERO,1980). It is not known if the two types of patchy input to the MT are in or out of register, which could be two interesting possibilities. At present, the functional significance of the uneven input to the cortex from the pulvinar is unknown. Acknowledgement-This study was supported by NIH grant EY-02686.
2228
C.-S. LIK and J. H. KAAS REFERENCES
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Trojanowski J. Q. & Jacobson S. (1976) Area1 and laminar distribution of some pulvinar cortical efferents in rhesus monkey. J. camp. Neural. 169, 371-392. WALKERA. E. (1938) The Primate Thaiamus. University of Chicago Press. WELLER,R. E. & KAAS, J. H. (1980) Cortical and subcortical connections of visual cortex in primates. In Multipk Cortictil Somatic Sensory-Motor, Visual and ,4uditory Areas and their Connections (ed. Woolsey, C. N.). Humana Press. Clifton, New Jersey. In Press. WINFIELDD. A., GATTERK. L. & POWELLT. P. S. (1975) Cerrtain connections of the visual cortex of the monkey shown by the use of horseradish peroxidase. Bruin Res. 92, 456-461. WONG-RILEYM. T. T. (1977) Connections between the pulvinar nucleus and the prestriate cortex in the squirrel monkey as revealed by peroxidase his&chemistry and autoradiography. Brain Res. 134, 249-267. (Accepted 3 July 1980)