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Peroxidase labeled subcortical afferents to pulvinar in rhesus monkey
144
Brah~ Re,war,#. t)7 (I975) 144 i5(,~ ElscvieJ Nclcntilic l~ublishirlg Compally, Amsterdam - Printed i~l The Nethe~lat~d~
Peroxidase labeled subcortical afferents to pulvinar in rhesus monkey
J O H N Q, T R O J A N O W S K I AND S T A N L E Y J A C O B S O N
Department of Anatomy, Tails University School of Medic#re, Boston, Mass. 02111 (U.S.A.) (Accepted June 25th, 1975)
With the exception of the tectopulvinar pathway the subcortical afferents to pulvinar still remain an enigma. In view of the suggestions by earlier authors, based largely on observations of normal material, that the pulvinar receives input from adjacent thalamic sensory relay nuclei, medial dorsal nucleus 18, amygdala 14 and retina 5, we have attempted to identify subcortical structures efferent to pulvinar in rhesus monkey using horseradish peroxidase (HRP). A preliminary report of these findings has appeared elsewhere 17. Four rhesus monkeys received unilateral injections of HRP into pulvinar subsequent to transection of the splenium of corpus callosum and visualization of this nucleus. In 5 additional monkeys bilateral stereotaxic injections were made using the atlas of Olszewski 13 for coordinates after first taking a zero reading from the habenular commissure subsequent to transection of the splenium. Injections were made using 10~ and 20~o aqueous horseradish peroxidase (Sigma VI) via a 10 #1 Hamilton syringe in volumes of 0.3-0.6 /zl. The aqueous solution also contained dissolved tritiated amino acids so that at a later time the efferents of pulvinar could be studied. The animals survived for 2-3 days and after being deeply anesthetized were perfused with a mixture of 0.5')~, paraformaldehyde and 2.5 ~; glutaraldehyde buffered with sodium cacodylate or phosphate buffer at pH 7.2 preceded by washing with a solution of 6 ~,i Dextran in 0.9 .'~osaline. The retinas as well as the upper 5-7 segments of cervical cord in addition to the brains were removed and the tissue was processed as previously described8,16 for HRP. A series of every tenth section cut at 40/~m in the stereotaxic plane or 80/~m in the parasagittal plane in the case of the retinas was examined for the presence of H R P positive neurons under dark- and light-field illumination using an X-Y plotter. The cover slips were then removed and the previously examined sections were stained with cresyl violet in order to determine the exact location of the H R P labeled cells. The injection sites were reconstructed and indicated on representative thalamic diagrams based on the atlas of Olszewski 13. Of the 14 attempted injections 12 were identified. In 2 animals, i.e. 4 and 5 (Fig. 2) in which bilateral injections were attempted, no injection site could be identified in one of the hemispheres of each animal. The needle tract could be identified but insufficient HRP was deposited in pulvinar due to plugging of the needle and
145 1
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. PM."
PM
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.
pM
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+ 1.5
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Fig. 1. Animals 1 and 2 with pulvinar injections made by direct visualization of pulvinar. The needle tract and area of tissue damage at injection site are indicated in black. Stippling indicates area in puvinar with heavy HRP staining and the slight leakage of tracer along the needle tract. See text for details. Abbreviations: L, nucleus limitans; MD, medial dorsal nucleus; MG, medial geniculate nucleus; PM, PL and PI, medial, lateral and inferior pulvinar nuclei respectively; SG, suprageniculate nucleus. The numbers under the thalamic diagrams refer to equivalent levels in Olszewski ]3. consequently there was no injection site and no evidence o f retrograde transport, while in the contralateral hemispheres in which the injection sites could be identified retrograde transport had occurred. A slight a m o u n t o f leakage o f H R P along the needle tract appears insignificant at the light microscope level. This assumption was supported by findings in other monkeys in which, although the needle passed through the foot region of somatosensory cortex, no H R P positive cells were observed in the appropriate parts of the ventral posterior lateral nucleus. Selected injection sites are illustrated in Figs. 1 and 2. The blackened area indicates tissue damage caused by the needle whereas the stippling indicates the presence o f the H R P substrate. The striking finding in all the material was the paucity of subcortical H R P positive neurons and the absence o f labeled neurons in pulvinar except at the injection site, even with relatively large injections as in animal 1 in Fig. 1. Nevertheless, H R P positive neurons were observed in cortex and in a limited n u m b e r o f subcortical sites in all 12 hemispheres. Labeled cortical neurons were seen only ipsilateral to the unilateral injections and preliminary observations indicate that these neurons are restricted to layers V and VI in accordance with observations in cat 15 and rat 8. Some subcortical neurons were observed to contain granules mimicking the appearance of H R P granules in dark-field illumination (Fig. 3). These granules were observed in neurons bilaterally in equal numbers in such areas as the median eminence,
146
3a
3L
ii
PM
+1.5
+0.9
~19
+03
.
PM
Pi
+ 2.7
+ 2.1
+0.0
+0.3
Fig. 2. Animals 3L and R, 4 and 5 with stereotaxic pulvinar injections. Injection sites are indicated as in Fig. 1. Abbreviations: C, caudate nucleus with subjacent stria terminalis and its bed nucleus; LG, lateral geniculate nucleus; LP, lateral posterior nucleus; PO, oral pulvinar; R, thalamic reticular nucleus; VPL, ventral posterior lateral nucleus. Other symbols as in Fig. 1. m a m m i l l a r y bodies, v e n t r o m e d i a l h y p o t h a l a m u s , s u b s t a n t i a nigra, p e r i a q u e d u c t a l gray, mesencephalic and p o n t i n e reticular f o r m a t i o n , trigeminal mesencephalic nucleus, locus ceruleus a n d the dorsal m o t o r nucleus o f the vagus. These granules m a y well be p i g m e n t granules since m a n y n e u r o n s c o n t a i n i n g them were d i s t r i b u t e d in a r e a s k n o w n to c o n t a i n m e l a n i n L G r a n u l e s in these neurons are u n r e l a t e d to H R P granules since they were seen in n e u r o n s bilaterally also in u n i n c u b a t e d sections. The H R P d a t a i n d i c a t e d t h a t 4 s u b c o r t i c a l sites p r o j e c t to p u l v i n a r : ctaustrum, t h a l a m i c reticular nucleus, d o r s a l lateral geniculate nucleus ( L G N ) and s u p e r i o r colliculus (Fig. 3). P e r o x i d a s e labeled n e u r o n s were observed in c l a u s t r u m ipsilateral to unilateral injections, a few such cells being f o u n d scattered t h r o u g h o u t c l a u s t r u m at m o s t levels. L a b e l e d n e u r o n s in t h a l a m i c reticular nucleus were likewise observed ipsilateral to unilateral injections l o c a t e d p r i m a r i l y at those levels in which the inj e c t i o n site was visible. L a b e l e d n e u r o n s were f o u n d in these two structures in all 12 hemispheres, two o f which (not illustrated here) had injection sites also involving Fig. 3. A and B: dark-field photomicrographs of neurons containing granules mimicking the appearante of HRP granules in locus ceruleus (A) and substantia nigra (B) × 600. Such neurons were seen consistently in several subcortical regions in both incubated and unincubated material and were therefore considered not to be HRP positive neurons. See text for details. C-H: dark-field photo' micrographs of HRP positive neurons in regions afferent to pulvinar. C: claustrum x 600. D: thalamic reticular nucleus ~." 600. E and F: superficial gray layer of superior co]liculus x 600 and >: 350 respectively. G and H: Lamina V[ of dorsal lateral geniculate nucleus ~< 600 and ~< 350 respectively.
0
0
148 oral pulvinar. It was concluded that all parts of pulvinar receive input fi'om these two structures. There is documentation of the tectopulvinar projection:~, I' but the ceils c~t origin of this pathway have not been characterized. The data derived from animal ! (Fig. 1) indicates that these cells are located in lamina 1I or the superficial gray layer of superior colliculus bilaterally, although they are more concentrated ipsilateral to the injection site and in the rostral third of this structure. A few such cells were observed with a similar distribution in a second animal (not illustrated here) with an injection affecting the medial most part of inferior pulvinar (Pl). Since cotlicular neurons were not labeled in any of the other 10 injected hemispheres including animal 2 (Fig. 1) the terminal field of this projection is probably restricted to the medial parts of PI and lateral pulvinar (PL). Evidence for an ipsilateral input from L G N to the lateral parts of PI, PI, and medial pulvinar (PM) could be adduced from findings in 8 of the injected hemispheres with injection sites affecting the lateral parts of pulvinar. Four of these injection sites are illustrated in Fig. 2. In these 4 cases H R P positive neurons were found in claustrum and thalamic reticular nucleus but in addition also in L G N . in animals 4 and 5, where only one of the attempted bilateral injections were found as mentioned above, peroxidase labeled neurons were found in these 3 sites only ipsilateral to the injection site. The H R P positive cells in LGN were found at all rostrocaudal levels of LGN and were concentrated in lamina VI although a rare labeled cell was observed in other parw)cellular lamina and none were noted in magnocellular L G N . The possibility that some of these peroxidase labeled neurons are also efferent to the thalamic reticular nucleus cannot be ruled out, but it seems unlikely that this is the primary region of termination of these neurons, since in animal 5, the needle tract did not pass through this structure yet labeled neurons were seen in LGN. All subcortica[ regions from rostral levels o f c a u d o p u t a m e n caudally to cervical cord segments 5 7 were examined for evidence of H R P positive neurons. Some injection sites involved pulvinar and adjacent structures but additional sites containing labeled neurons in these cases could be ruled out as being afferent to pulvinar on the basis of the injection sites confined to pulvinar alone, and pulvinar input is therefore thought to originate subcortically only from the 4 regions mentioned above. There was no evidence of input to pulvinar from amygdala, medial dorsal, medial geniculate or ventral posterior lateral nuclei as suggested in the earlier literature ~4,~8. 1he absence of peroxidase labeled neurons in the dorsal column nuclei, dorsal horn and inferior colliculus confirms results of earlier studies 1.4.j°. Finally, the recent report a of bilateral retinal input to Pi could not be corroborated since the retinas from animals with injection sites involving PI, PL or PM were without H R P labeled neurons. This negative result is in agreement with an earlier autoradiographic study in rhesus monkey 7. The fact that the subcortical input to pulvinar is derived from only 4 structures: claustrum, thalamic reticular nucleus, L G N and superior colliculus, has implications for any hypothesis regarding pulvinar function, as does the fact that in the pul~'inar itself there appears to be little internal circuitry since H R P labeled neurons were
149 observed in pulvinar only in the immediate vicinity of the injection site. This suggests that the different pulvinar subnuclei are not in communication with one another, at least not without the intervention of another neuron situated in some extrapulvinar location. The implication of these findings is to restrict to a few sites the neurons from which the sensory information known to reach pulvinar 9 can be derived. Visual input to pulvinar may originate from superior colliculus, LGN, striate or extra-striate visual responsive cortex. Information regarding auditory and somatosensory stimuli can only be derived from sources many synapses removed from the original stimuli and most likely candidates are primary and/or secondary auditory and somatosensory cortex. There is a bias in pulvinar connectivity in favor of structures related to the visual system. This plus certain physiological data 1° has suggested the possibility that pulvinar may play some role in processing visual information despite negative behavioral data 11. Recent evidence that evoked potentials recorded in PI of monkeys undergo changes similar to those observed in circumstriate cortex during the acquisition phase of learning a visual discrimination task v, suggest that this hypothesis should not be abandoned. However, it should not be overlooked that pulvinar has connections with cortical regions with sensory functions other than visually related ones as well as to association cortical areas a6,18. In view of the above, it x~ould seem appropriate to consider the role played by those cortical regions with which the pulvinar is connected in the elaboration of primate behavior in searching for models for pulvinar function. The authors thank Mr. Jonathan Ginzberg for his expert technical assistance. Doctor J. Brinkman is thanked for her help with different aspects of the experiments. This investigation was supported by U.S.P.H.S. Grant NS 07666. I BARNES, W. T., MAGOUN, H. W., AND RANSON, S. W., The ascending auditory pathway in the brainstem of the monkey, J. comp. Neurol., 79 (1943) 129-152. 2 BAZELON, M., FENICHEE, G. M., AND RANDALL, J., Studies on neuromelanin. I. A melanin system in the human adult brainstem, Neurology (Minneap.), 17 (1967) 512-519. 3 BENEVENTO, L. A., AND FALLON, P. O., Superficial versus deep laminar efferents of superior colliculus: comparison with orbital cortex efferents in rhesus monkey, Anat. Rec., 178 (1974) 309. 4 BOWSHER, D., Projection of the gracile and cuneate nuclei in Macaea mulatta: an experimental degeneration study, J. comp. Neurol., 110 (i958) 133-155. 5 CAMPOS-ORTEGA,J. A., HAYHOW, W. R., AND CULVER, P. F. V. DE, A note on the problem of retinal projections to the inferior pulvinar nucleus of primates, Brain Research, 22 (1970) 126-130. 6 GOULD, J. E., CHALUPA, L. M., AND LINDSLEY, D. B., Modifications of pulvinar and geniculocortical evoked potentials during visual discrimination learning in monkeys, Electroenceph. clin. Neurophysiol., 36 (1974) 639-649. 7 HENDRICKSON, A., WILSON, M. E., AND TOYNE, M. J., The distribution of optic nerve fibers in Macaca mulatta, Brain Research, 23 (1970) 425-427. 8 JACOBSON, S., AND TROJANOWSKI, J. Q., Corticothalamic neurons and thalamocortical terminal fields: an investigation in rat using horseradish peroxidase and autoradiography, Brain Research, 85 (1975) 385401. 9 MATHERS, L. H., AND RAPISARDI, S. C., Visual and somatosensory receptive fields of neurons in the squirrel monkey pulvinar, Brain Research, 64 (1973) 65-83. 10 MEHLER, W. R., FEFERMAN, M. E., AND NAUTA, W. H., Ascending axon degeneration following anterolateral cordotomy. An experimental study in the monkey, Brain, 83 (1960) 718-750.
150 1 [ MISHKIN, M., Cortical visual areas and their interaction. In A. G. KAR("ZMAP-Ar",l)J. ( . [~ ~1 ~; (Eds.), Brain and Hunum Beharh)r, Springer, New York, 1972, pp. 187-208. 12 MYEI~s, R. E., Projections of the superior colliculus in the monkey, Anat. Rcc., 145 (1963~ 2~4. 13 OLSZI~WSKL J., The Thalamu,~ ~/' the Macaca nlttlatta." All ,4tlus [or U~e with the Stere~tJ.vic btstrumettt, Karger, Basel, 1952, 14 PAPEZ, J, W., Connections of pulvinar, ,4rch. Neurol. Psychiat. (Chic.), 41 (1939) 277 289. [5 ROMAGNANf), M. A., ANt) MA('IEWICZ, R. J,, Peroxidase labelling of motor cortex neurons projecting to the ventrolateral nucleus in the cat, Brain Research, 83 (1975) 46%473. 16 TROJANOWSKI, J. Q., ANt) JACOBSON, S., Medial pulvinar afferents to frontal eye fields in rhesus monkey demonstrated by horseradish peroxidase, Bra#t Research, 80 (1974) 395-411. 17 TROJANOWSKI, J. Q., The question of intrathalamic connections of pulvinar in rhesus monkey, Anat. Rec., 181 (1975)495. 18 WALKER, A. E., The Prhmlte Thalamus, Univ. Chicago Press, Chicago, II1., 193~.
Brah~ Re,war,#. t)7 (I975) 144 i5(,~ ElscvieJ Nclcntilic l~ublishirlg Compally, Amsterdam - Printed i~l The Nethe~lat~d~
Peroxidase labeled subcortical afferents to pulvinar in rhesus monkey
J O H N Q, T R O J A N O W S K I AND S T A N L E Y J A C O B S O N
Department of Anatomy, Tails University School of Medic#re, Boston, Mass. 02111 (U.S.A.) (Accepted June 25th, 1975)
With the exception of the tectopulvinar pathway the subcortical afferents to pulvinar still remain an enigma. In view of the suggestions by earlier authors, based largely on observations of normal material, that the pulvinar receives input from adjacent thalamic sensory relay nuclei, medial dorsal nucleus 18, amygdala 14 and retina 5, we have attempted to identify subcortical structures efferent to pulvinar in rhesus monkey using horseradish peroxidase (HRP). A preliminary report of these findings has appeared elsewhere 17. Four rhesus monkeys received unilateral injections of HRP into pulvinar subsequent to transection of the splenium of corpus callosum and visualization of this nucleus. In 5 additional monkeys bilateral stereotaxic injections were made using the atlas of Olszewski 13 for coordinates after first taking a zero reading from the habenular commissure subsequent to transection of the splenium. Injections were made using 10~ and 20~o aqueous horseradish peroxidase (Sigma VI) via a 10 #1 Hamilton syringe in volumes of 0.3-0.6 /zl. The aqueous solution also contained dissolved tritiated amino acids so that at a later time the efferents of pulvinar could be studied. The animals survived for 2-3 days and after being deeply anesthetized were perfused with a mixture of 0.5')~, paraformaldehyde and 2.5 ~; glutaraldehyde buffered with sodium cacodylate or phosphate buffer at pH 7.2 preceded by washing with a solution of 6 ~,i Dextran in 0.9 .'~osaline. The retinas as well as the upper 5-7 segments of cervical cord in addition to the brains were removed and the tissue was processed as previously described8,16 for HRP. A series of every tenth section cut at 40/~m in the stereotaxic plane or 80/~m in the parasagittal plane in the case of the retinas was examined for the presence of H R P positive neurons under dark- and light-field illumination using an X-Y plotter. The cover slips were then removed and the previously examined sections were stained with cresyl violet in order to determine the exact location of the H R P labeled cells. The injection sites were reconstructed and indicated on representative thalamic diagrams based on the atlas of Olszewski 13. Of the 14 attempted injections 12 were identified. In 2 animals, i.e. 4 and 5 (Fig. 2) in which bilateral injections were attempted, no injection site could be identified in one of the hemispheres of each animal. The needle tract could be identified but insufficient HRP was deposited in pulvinar due to plugging of the needle and
145 1
p ~
\
+ 2.1
. PM."
PM
":::::"
.-.""
.
pM
..-}?....."
+ 1.5
+1.5
..:':..
+0.9
+0.3
- 1.0
+0.9
Fig. 1. Animals 1 and 2 with pulvinar injections made by direct visualization of pulvinar. The needle tract and area of tissue damage at injection site are indicated in black. Stippling indicates area in puvinar with heavy HRP staining and the slight leakage of tracer along the needle tract. See text for details. Abbreviations: L, nucleus limitans; MD, medial dorsal nucleus; MG, medial geniculate nucleus; PM, PL and PI, medial, lateral and inferior pulvinar nuclei respectively; SG, suprageniculate nucleus. The numbers under the thalamic diagrams refer to equivalent levels in Olszewski ]3. consequently there was no injection site and no evidence o f retrograde transport, while in the contralateral hemispheres in which the injection sites could be identified retrograde transport had occurred. A slight a m o u n t o f leakage o f H R P along the needle tract appears insignificant at the light microscope level. This assumption was supported by findings in other monkeys in which, although the needle passed through the foot region of somatosensory cortex, no H R P positive cells were observed in the appropriate parts of the ventral posterior lateral nucleus. Selected injection sites are illustrated in Figs. 1 and 2. The blackened area indicates tissue damage caused by the needle whereas the stippling indicates the presence o f the H R P substrate. The striking finding in all the material was the paucity of subcortical H R P positive neurons and the absence o f labeled neurons in pulvinar except at the injection site, even with relatively large injections as in animal 1 in Fig. 1. Nevertheless, H R P positive neurons were observed in cortex and in a limited n u m b e r o f subcortical sites in all 12 hemispheres. Labeled cortical neurons were seen only ipsilateral to the unilateral injections and preliminary observations indicate that these neurons are restricted to layers V and VI in accordance with observations in cat 15 and rat 8. Some subcortical neurons were observed to contain granules mimicking the appearance of H R P granules in dark-field illumination (Fig. 3). These granules were observed in neurons bilaterally in equal numbers in such areas as the median eminence,
146
3a
3L
ii
PM
+1.5
+0.9
~19
+03
.
PM
Pi
+ 2.7
+ 2.1
+0.0
+0.3
Fig. 2. Animals 3L and R, 4 and 5 with stereotaxic pulvinar injections. Injection sites are indicated as in Fig. 1. Abbreviations: C, caudate nucleus with subjacent stria terminalis and its bed nucleus; LG, lateral geniculate nucleus; LP, lateral posterior nucleus; PO, oral pulvinar; R, thalamic reticular nucleus; VPL, ventral posterior lateral nucleus. Other symbols as in Fig. 1. m a m m i l l a r y bodies, v e n t r o m e d i a l h y p o t h a l a m u s , s u b s t a n t i a nigra, p e r i a q u e d u c t a l gray, mesencephalic and p o n t i n e reticular f o r m a t i o n , trigeminal mesencephalic nucleus, locus ceruleus a n d the dorsal m o t o r nucleus o f the vagus. These granules m a y well be p i g m e n t granules since m a n y n e u r o n s c o n t a i n i n g them were d i s t r i b u t e d in a r e a s k n o w n to c o n t a i n m e l a n i n L G r a n u l e s in these neurons are u n r e l a t e d to H R P granules since they were seen in n e u r o n s bilaterally also in u n i n c u b a t e d sections. The H R P d a t a i n d i c a t e d t h a t 4 s u b c o r t i c a l sites p r o j e c t to p u l v i n a r : ctaustrum, t h a l a m i c reticular nucleus, d o r s a l lateral geniculate nucleus ( L G N ) and s u p e r i o r colliculus (Fig. 3). P e r o x i d a s e labeled n e u r o n s were observed in c l a u s t r u m ipsilateral to unilateral injections, a few such cells being f o u n d scattered t h r o u g h o u t c l a u s t r u m at m o s t levels. L a b e l e d n e u r o n s in t h a l a m i c reticular nucleus were likewise observed ipsilateral to unilateral injections l o c a t e d p r i m a r i l y at those levels in which the inj e c t i o n site was visible. L a b e l e d n e u r o n s were f o u n d in these two structures in all 12 hemispheres, two o f which (not illustrated here) had injection sites also involving Fig. 3. A and B: dark-field photomicrographs of neurons containing granules mimicking the appearante of HRP granules in locus ceruleus (A) and substantia nigra (B) × 600. Such neurons were seen consistently in several subcortical regions in both incubated and unincubated material and were therefore considered not to be HRP positive neurons. See text for details. C-H: dark-field photo' micrographs of HRP positive neurons in regions afferent to pulvinar. C: claustrum x 600. D: thalamic reticular nucleus ~." 600. E and F: superficial gray layer of superior co]liculus x 600 and >: 350 respectively. G and H: Lamina V[ of dorsal lateral geniculate nucleus ~< 600 and ~< 350 respectively.
0
0
148 oral pulvinar. It was concluded that all parts of pulvinar receive input fi'om these two structures. There is documentation of the tectopulvinar projection:~, I' but the ceils c~t origin of this pathway have not been characterized. The data derived from animal ! (Fig. 1) indicates that these cells are located in lamina 1I or the superficial gray layer of superior colliculus bilaterally, although they are more concentrated ipsilateral to the injection site and in the rostral third of this structure. A few such cells were observed with a similar distribution in a second animal (not illustrated here) with an injection affecting the medial most part of inferior pulvinar (Pl). Since cotlicular neurons were not labeled in any of the other 10 injected hemispheres including animal 2 (Fig. 1) the terminal field of this projection is probably restricted to the medial parts of PI and lateral pulvinar (PL). Evidence for an ipsilateral input from L G N to the lateral parts of PI, PI, and medial pulvinar (PM) could be adduced from findings in 8 of the injected hemispheres with injection sites affecting the lateral parts of pulvinar. Four of these injection sites are illustrated in Fig. 2. In these 4 cases H R P positive neurons were found in claustrum and thalamic reticular nucleus but in addition also in L G N . in animals 4 and 5, where only one of the attempted bilateral injections were found as mentioned above, peroxidase labeled neurons were found in these 3 sites only ipsilateral to the injection site. The H R P positive cells in LGN were found at all rostrocaudal levels of LGN and were concentrated in lamina VI although a rare labeled cell was observed in other parw)cellular lamina and none were noted in magnocellular L G N . The possibility that some of these peroxidase labeled neurons are also efferent to the thalamic reticular nucleus cannot be ruled out, but it seems unlikely that this is the primary region of termination of these neurons, since in animal 5, the needle tract did not pass through this structure yet labeled neurons were seen in LGN. All subcortica[ regions from rostral levels o f c a u d o p u t a m e n caudally to cervical cord segments 5 7 were examined for evidence of H R P positive neurons. Some injection sites involved pulvinar and adjacent structures but additional sites containing labeled neurons in these cases could be ruled out as being afferent to pulvinar on the basis of the injection sites confined to pulvinar alone, and pulvinar input is therefore thought to originate subcortically only from the 4 regions mentioned above. There was no evidence of input to pulvinar from amygdala, medial dorsal, medial geniculate or ventral posterior lateral nuclei as suggested in the earlier literature ~4,~8. 1he absence of peroxidase labeled neurons in the dorsal column nuclei, dorsal horn and inferior colliculus confirms results of earlier studies 1.4.j°. Finally, the recent report a of bilateral retinal input to Pi could not be corroborated since the retinas from animals with injection sites involving PI, PL or PM were without H R P labeled neurons. This negative result is in agreement with an earlier autoradiographic study in rhesus monkey 7. The fact that the subcortical input to pulvinar is derived from only 4 structures: claustrum, thalamic reticular nucleus, L G N and superior colliculus, has implications for any hypothesis regarding pulvinar function, as does the fact that in the pul~'inar itself there appears to be little internal circuitry since H R P labeled neurons were
149 observed in pulvinar only in the immediate vicinity of the injection site. This suggests that the different pulvinar subnuclei are not in communication with one another, at least not without the intervention of another neuron situated in some extrapulvinar location. The implication of these findings is to restrict to a few sites the neurons from which the sensory information known to reach pulvinar 9 can be derived. Visual input to pulvinar may originate from superior colliculus, LGN, striate or extra-striate visual responsive cortex. Information regarding auditory and somatosensory stimuli can only be derived from sources many synapses removed from the original stimuli and most likely candidates are primary and/or secondary auditory and somatosensory cortex. There is a bias in pulvinar connectivity in favor of structures related to the visual system. This plus certain physiological data 1° has suggested the possibility that pulvinar may play some role in processing visual information despite negative behavioral data 11. Recent evidence that evoked potentials recorded in PI of monkeys undergo changes similar to those observed in circumstriate cortex during the acquisition phase of learning a visual discrimination task v, suggest that this hypothesis should not be abandoned. However, it should not be overlooked that pulvinar has connections with cortical regions with sensory functions other than visually related ones as well as to association cortical areas a6,18. In view of the above, it x~ould seem appropriate to consider the role played by those cortical regions with which the pulvinar is connected in the elaboration of primate behavior in searching for models for pulvinar function. The authors thank Mr. Jonathan Ginzberg for his expert technical assistance. Doctor J. Brinkman is thanked for her help with different aspects of the experiments. This investigation was supported by U.S.P.H.S. Grant NS 07666. I BARNES, W. T., MAGOUN, H. W., AND RANSON, S. W., The ascending auditory pathway in the brainstem of the monkey, J. comp. Neurol., 79 (1943) 129-152. 2 BAZELON, M., FENICHEE, G. M., AND RANDALL, J., Studies on neuromelanin. I. A melanin system in the human adult brainstem, Neurology (Minneap.), 17 (1967) 512-519. 3 BENEVENTO, L. A., AND FALLON, P. O., Superficial versus deep laminar efferents of superior colliculus: comparison with orbital cortex efferents in rhesus monkey, Anat. Rec., 178 (1974) 309. 4 BOWSHER, D., Projection of the gracile and cuneate nuclei in Macaea mulatta: an experimental degeneration study, J. comp. Neurol., 110 (i958) 133-155. 5 CAMPOS-ORTEGA,J. A., HAYHOW, W. R., AND CULVER, P. F. V. DE, A note on the problem of retinal projections to the inferior pulvinar nucleus of primates, Brain Research, 22 (1970) 126-130. 6 GOULD, J. E., CHALUPA, L. M., AND LINDSLEY, D. B., Modifications of pulvinar and geniculocortical evoked potentials during visual discrimination learning in monkeys, Electroenceph. clin. Neurophysiol., 36 (1974) 639-649. 7 HENDRICKSON, A., WILSON, M. E., AND TOYNE, M. J., The distribution of optic nerve fibers in Macaca mulatta, Brain Research, 23 (1970) 425-427. 8 JACOBSON, S., AND TROJANOWSKI, J. Q., Corticothalamic neurons and thalamocortical terminal fields: an investigation in rat using horseradish peroxidase and autoradiography, Brain Research, 85 (1975) 385401. 9 MATHERS, L. H., AND RAPISARDI, S. C., Visual and somatosensory receptive fields of neurons in the squirrel monkey pulvinar, Brain Research, 64 (1973) 65-83. 10 MEHLER, W. R., FEFERMAN, M. E., AND NAUTA, W. H., Ascending axon degeneration following anterolateral cordotomy. An experimental study in the monkey, Brain, 83 (1960) 718-750.
150 1 [ MISHKIN, M., Cortical visual areas and their interaction. In A. G. KAR("ZMAP-Ar",l)J. ( . [~ ~1 ~; (Eds.), Brain and Hunum Beharh)r, Springer, New York, 1972, pp. 187-208. 12 MYEI~s, R. E., Projections of the superior colliculus in the monkey, Anat. Rcc., 145 (1963~ 2~4. 13 OLSZI~WSKL J., The Thalamu,~ ~/' the Macaca nlttlatta." All ,4tlus [or U~e with the Stere~tJ.vic btstrumettt, Karger, Basel, 1952, 14 PAPEZ, J, W., Connections of pulvinar, ,4rch. Neurol. Psychiat. (Chic.), 41 (1939) 277 289. [5 ROMAGNANf), M. A., ANt) MA('IEWICZ, R. J,, Peroxidase labelling of motor cortex neurons projecting to the ventrolateral nucleus in the cat, Brain Research, 83 (1975) 46%473. 16 TROJANOWSKI, J. Q., ANt) JACOBSON, S., Medial pulvinar afferents to frontal eye fields in rhesus monkey demonstrated by horseradish peroxidase, Bra#t Research, 80 (1974) 395-411. 17 TROJANOWSKI, J. Q., The question of intrathalamic connections of pulvinar in rhesus monkey, Anat. Rec., 181 (1975)495. 18 WALKER, A. E., The Prhmlte Thalamus, Univ. Chicago Press, Chicago, II1., 193~.