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The influence of unilateral visual deprivation on optic centers
763
BRAIN RESEARCH
Short Communications
The influence of unilateral visual deprivation on optic centers The visual system has repeatedly been used as a model for studies on the significance of afferent stimuli for the maintenance of nervous centers. The main advantages of the visual system are as follows: the sensory inputs, which can be easily modified and quantified, are mainly formed by optic fibers. In lower vertebrates and mammals the influx is lateralized because of more or less complete crossing of fibers in the optic chiasma. Thus unilateral deafferentation produces unilateral effect. Morphological changes induced by visual deprivation were studied on dark-reared, enucleated or lid-sutured animals, with or without previous visual experiences. The first method causes bilateral effects so that another group of animals is necessary for control. The interindividual dispersion which might, to a certain extent, distort the results could be avoided only by pair comparison. This can be achieved either by unilateral enucleation or lid-suturing. Enucleation, a suitable method for determining degenerative and transneural changes, causes, however, an irreversible state. The advantages of both preceding methods are included in the lid-suturing. The compensatory activation of other sensory modalities by rearing in darkness is thus avoided s. Recently the influence of camplex environment on rat's brain morphology and biochemistry was clearly demonstrated1, a. In this paper the optic centers of rats raised with unilateral visual deprivation in an enriched environment were studied. White rats (Lewis strain) were used throughout. The visual deprivation was achieved by unilateral lid-suture (on the right side) in 14- or 15-day-old animals. One week after the operation rats were transferred from normal cages into larger ones (57 x 43 x 50 cm) for 8-9 weeks. There they were exposed to different kinds of visual stimulation and had greater movement opportunity. After finishing the experiment, animals were sacrificed in allobarbital anesthesia by perfusion with formolsaline. The material embedded in celioidin was cut serially in 20 ff thick sections from which every third was stained with cresylviolet. Relevant parts ot the brain were redrawn at 40 x magnification. The thickness of the visual cortex was measured in a strip of 0.5 x 1.0 mm at 0.1 mm intervals a. This strip was l mm distant from the white matter elevation and contained the rostral parts of area 18 and 17. Because of difficulties in volume determination of the superior colliculus (CS) the thickness of the stratum griseum superficiale was measured in the same way as in the cortex. A strip of 0.36 × 1.0 mm located 0.5 mm from the medial aspect was used and its thickness was measured at 0.1 mm intervals. The volume of the dorsal part of the lateral geniculate body was determined by planimetry. The volume of a part of the intracerebral course of the optic tract (TO) was measured as well. The intracerebral part of TO (from the complete penetration into the brain till the temporal cone of the lateral ventricle) is less subject to deformation during the histological procedure than its extracerebral course. In another group of animals unilateral enucleation was made (on Brain Research, 6 (1967) 763-766
764
SHORT COMMUNICATIONS
the right side). After 7 days the animals were killed and brain sections were stained with the N a u t a method. The n u m b e r o f uncrossed optic fibers could, to some extent, influence the paired comparison o f the normal and deprived side. Therefore white rats were used where the n u m b e r o f uncrossed fibers is practically negligible s. Because L u n d ' s observations were carried out in Wistar and Glaxo strains and ours in the Lewis strain we have repeated those experiments using the N a u t a technique. In the ipsilateral dorsal part of the lateral geniculate b o d y only few degenerated fibers were observed with prevalent location in its medial part. Some dispersed fibers were found in the ventral part o f the lateral geniculate body. Some degenerated axons in the optic stratum o f the superior colliculus were mainly located in its medial part and very few ones in the superficial grey layer. The contralateral distribution o f retinal fiber was in agreement with H a y h o w ' s description 6. Structures %r volumetric studies were chosen according to the terminal distribution o f retinofugal fibers. Clear-cut cytoarchitectural limitation o f each o f them was a necessary prerequisite for measuring. Although m a n y subcortical nuclei with retinal input have been described, the above criterion has considerably restricted their number. I n t h a l a m i e nuclei only the dorsal part of lateral geniculate b o d y ( G L D ) could be evaluated. Although the ventral part o f lateral geniculate b o d y is invaded by a number o f retinal fibers 6 it was not taken into account because o r its fusion with zona incerta. The volume o f the G L D ipsilateral to the lid-sutured eye was taken as 100 % (Table I). The decrease in volume o f the G L D contralateral to the lid-sutured TABLE I DIFFERENCEOF METRICVALUESBETWEENRIGHTAND LEFTVISUALCENTERSIN PERCENTAGES Metric values of visual centers of the right side corresponding to the open eye were taken as 100%. TO = tractus opticus; CS = colliculus superior; GLD = corpus geniculatum laterale pars dorsalis. Cortex
Experiment n = 18 Control n = 10
Subcortex
TO
I I - VI
II-IV
V- V1
GLD
CS
6.62 4- 1.48 -t = 4.47 0.52 + 1.14 t = 0.46
8.55 + 1.68 t = 5.08 1.39 4- 1.98 t = 0.71
5.07 + 2.27 t = 2.24 1.63 4- 1.20 t = 1.35
5.90 4- 1.01 t = 5.84 1.18 4- 3.24 t = 0.36
1.14 -q- 2.27 t = 0.50 0.24 4- 2.74 t = 0.09
0.53 i 1.13 t = 0.47 1.15 4- 2.88 t = 0.40
eye was 5.9 %. N o consistent difference could be determined in the thickness o f the stratum superficiale colliculi superioris. The depth o f the visual cortex from layer I I - V I and thickness o f layers I I - I V and V - V I were measured separately. The greatest difference was found in layer I I - I V : 8.6 %. N o a s y m m e t r y could be determined in the volume o f TO. Differences between the deprived and control side are summarized in Table I. The method of visual deprivation by lid closure was used in mice 1°, in kittensT,13,14, in rabbits, cats and dogs 1~. M a r k e d histological changes without signifiBrain Research, 6 (1967) 763-766
SHORT COMMUNICATIONS
765
cant alteration of metabolic activity in G L D layers fed by the deprived eye were shown by Wiesel and Hube113 and Kupfer and Palmer 7 in kittens having no previous visual experience. Using the same method in rats no such obvious differences in G L D structure were observed. However, when comparing the volumes of dorsal geniculate bodies receiving inputs from the covered and uncovered eye significant differences were obtained. Apparently species differences exist; the higher the subject's position in the phylogenetic scale, the greater its susceptibility to the experimental treatment. The relative importance of the amount of light reaching the retina through the occlusion follows from the extent of cell atrophy in cat, due to deprivation and deafferentation2,13. Moderate findings in monocular deprivation with translucent cover and the complete absence of changes when suturing the nictitating membrane across the cornea favor this assumption. In rats, where the lids are considerably thinner than in kittens, more intense retinal illumination could be expected. Thus our results could be compared with those obtained by translucent contact occluder in kittens la. By general observation Terry e t al. 1o were not able to demonstrate any difference between both G L D in mice with unilateral eye closure. The same was true for our material; only quantitative evaluation revealed the difference. We were not able to find any lateralized effect due to monocular closure in the CS, namely in the stratum griseum superficiale. Similarly, no changes were observed by Wiesel and Hubel la who did not mention, however, which part of CS was under study. The results of Umrath 12 and Gyllensten et al. 4 concern the stratum opticum and cannot be compared with ours for the stratum griseum superficiale. As half of the retinal fibers are distributed to the CSe, 11 the negative results are surprising enough. The non-visual input could be taken into account. The spinal, trigeminal and reticular afferents terminate mainly in deeper layers of CS so that their influence upon the upper layers would be indirect only. The most probable explanation of our negative results is the different nature of information transmitted to the CS and GLD. information about general level of illumination and its changes, which is necessary for unconditioned reactions, is not influenced by this kind o! deprivation. Significant decrease in volume of internuclear material in the optic stratum of CS in Gyllensten's 4 experiments with dark-reared mice supports this idea. Significant decrease in the thickness and cell density of the visual cortex with prevalence of changes in layers II-IV was observed 4.1~. Wiesel and Hube114 were not able to demonstrate obvious anatomical changes but profound physiological deficits in the visual area. It is mainly due to the binocular input of the majority of cortical cells. In rats, on the other hand, the effect of visual deprivation is lateralized due to the minimum of uncrossed fibers. The commissural fibers being distributed in the visual cortex very unequally, mainl~ in its lateral part a, do not disturb this laterality because our measurements were carried out in its medial part. This seems to be the reason why the closure of one eye has the same effect on the visual cortex and on the GLD. Greater differences in the thickness of layers II-IV as compared with layers V-VI are in agreement with terminal distribution of th~ optic radiation. Summing up: monocular lid closure causes significant decrease in the volume of the contralateral visual cortex and G L D but does not affect CS and TO. The Brain Research, 6 (1967) 763-766
766
SHORT COMMUNICATIONS
a b o v e results seem to indicate t h a t these changes are n o t degenerative in nature. T h e c o m p a r i s o n o f o u r d a t a with T s a n g ' s 11 results in enucleated rats (obvious v o l u m e decrease o f relevant G L D a n d CS with m o d e r a t e changes in the visual cortex) supp o r t s this a s s u m p t i o n . A l t h o u g h y o u n g a n i m a l s were used in o u r e x p e r i m e n t s we d o n o t s u p p o s e t h a t the described a s y m m e t r y is exclusively due to g r o w t h i n h i b i t i o n . U n e q u i v o c a l results were o b t a i n e d in G L D a n d CS a l t h o u g h the time courses o f m a t u r a t i o n o f diencephalic a n d mesencephalic structures are the same. G y l l e n s t e n ' s 4 finding o f decrease in the v o l u m e o f i n t e r n u c l e a r m a t e r i a l in visual cortex, G L D a n d CS in visually experienced d a r k - r e a r e d mice seems to j u s t i f y this conclusion. T h e a u t h o r w o u l d like to express her a p p r e c i a t i o n to Prof. R. Hassler for his help in the c y t o a r c h i t e c t o n i c d e t e r m i n a t i o n o f t h e visual cortex which was d o n e in the D e p a r t m e n t o f N e u r o a n a t o m y o f the M a x - P l a n c k - I n s t i t u t e in F r a n k f u r t / M . Institute of Physiology, Czechoslovak Academy of Sciences, Prague (Czechoslovakia)
E. FIFKOVA
1 BENNET,E. L., DIAMOND,M. C., KRECH, D., AND ROSENZWEIO,M. R., Chemical and anatomical plasticity of brain, Science, 146 (1964) 610-619. 2 COOK, W. H., WALTER,J. H., AND BAng, M. L., Cytological study of transneuronal atrophy in the cat and rabbit, J. comp. Neurol., 94 (1951) 267-292. 3 DIAMOND,M. C., KRECH, D., AND ROSEIqZWEIG,M. R., The effect of an enriched environment on the histology of rat cerebral cortex, J. comp. NeuroL, 123 (1964) 111-120. 4 GYLLENSTEN,L., MALMFORS,T., AND NORRLIN, M.-L., Effect of visual deprivation of the optic centers of growing and adult mice, J. comp. Neurol., 124 (1965) 149-160. 5 GYLLENSTEN,L., MALMFORS,T., AND NORRUN, M.-L., Growth alteration in the auditory cortex of visually deprived mice, J. comp. Neurol., 126 (1966) 463-470. 6 HAYHOW,W. R., SEFTON,A., AND WEBB, C., Primary optic centers of the rat in relation to the terminal distribution of the crossed and uncrossed optic nerve fibers, J. comp. Neurol., 118 (1962) 295-322. 7 KtrPFER, G., AND PALMER,P., Lateral geniculate nucleus: histological and cytochemical changes following afferent denervation and visual deprivation, Exp. Neurol., 9 (1964) 400-409. 8 LONO,R. D., Uncrossed visual pathways of hooded and albino rats, Science, 149 (1965) 1506-1507. 9 NAUTA,W. J. H., AND BUCHER, V. M., Efferent connections of the striate center in the albino rat, J. comp. Nearol., 100 (1954) 257-285. 10 TERRY,R.. J., ROLAND,A. L., AND RACE,J., Jr., Effect of eye enucleation and eyelid closure upon the brain and associated visual structures in the mouse, J. exp. Zool., 150 (1962) 165-184. 11 TSANG,J., Visual centers in blinded rats, J. comp. Neurol., 66 (1936) 211-262. 12 UMRATH,K., Histologische Ver~mderungen im Gehirn yon Tieren nach Ausschaltung yon Augen durch Verniihen der Lider oder durch Exstirpation,.~7. Biol., 115 (1965) 99-118. 13 WmSEL,T. N., AND HUBEL,D. H., Effects of visual deprivation on morphology and physiology of cells in the cat's lateral geniculate body, J. NeurophysioL, 26 (1963) 978-993. 14 WIESEL,T. N., AND HtJaEL, D. H., Single-cell responses in striate cortex of kittens deprived of vision in one eye, J. Neurophysiol., 26 (1963) 1003-1017. (Accepted September 27th, 1967)
Brain Research, 6 (1967) 763-766
BRAIN RESEARCH
Short Communications
The influence of unilateral visual deprivation on optic centers The visual system has repeatedly been used as a model for studies on the significance of afferent stimuli for the maintenance of nervous centers. The main advantages of the visual system are as follows: the sensory inputs, which can be easily modified and quantified, are mainly formed by optic fibers. In lower vertebrates and mammals the influx is lateralized because of more or less complete crossing of fibers in the optic chiasma. Thus unilateral deafferentation produces unilateral effect. Morphological changes induced by visual deprivation were studied on dark-reared, enucleated or lid-sutured animals, with or without previous visual experiences. The first method causes bilateral effects so that another group of animals is necessary for control. The interindividual dispersion which might, to a certain extent, distort the results could be avoided only by pair comparison. This can be achieved either by unilateral enucleation or lid-suturing. Enucleation, a suitable method for determining degenerative and transneural changes, causes, however, an irreversible state. The advantages of both preceding methods are included in the lid-suturing. The compensatory activation of other sensory modalities by rearing in darkness is thus avoided s. Recently the influence of camplex environment on rat's brain morphology and biochemistry was clearly demonstrated1, a. In this paper the optic centers of rats raised with unilateral visual deprivation in an enriched environment were studied. White rats (Lewis strain) were used throughout. The visual deprivation was achieved by unilateral lid-suture (on the right side) in 14- or 15-day-old animals. One week after the operation rats were transferred from normal cages into larger ones (57 x 43 x 50 cm) for 8-9 weeks. There they were exposed to different kinds of visual stimulation and had greater movement opportunity. After finishing the experiment, animals were sacrificed in allobarbital anesthesia by perfusion with formolsaline. The material embedded in celioidin was cut serially in 20 ff thick sections from which every third was stained with cresylviolet. Relevant parts ot the brain were redrawn at 40 x magnification. The thickness of the visual cortex was measured in a strip of 0.5 x 1.0 mm at 0.1 mm intervals a. This strip was l mm distant from the white matter elevation and contained the rostral parts of area 18 and 17. Because of difficulties in volume determination of the superior colliculus (CS) the thickness of the stratum griseum superficiale was measured in the same way as in the cortex. A strip of 0.36 × 1.0 mm located 0.5 mm from the medial aspect was used and its thickness was measured at 0.1 mm intervals. The volume of the dorsal part of the lateral geniculate body was determined by planimetry. The volume of a part of the intracerebral course of the optic tract (TO) was measured as well. The intracerebral part of TO (from the complete penetration into the brain till the temporal cone of the lateral ventricle) is less subject to deformation during the histological procedure than its extracerebral course. In another group of animals unilateral enucleation was made (on Brain Research, 6 (1967) 763-766
764
SHORT COMMUNICATIONS
the right side). After 7 days the animals were killed and brain sections were stained with the N a u t a method. The n u m b e r o f uncrossed optic fibers could, to some extent, influence the paired comparison o f the normal and deprived side. Therefore white rats were used where the n u m b e r o f uncrossed fibers is practically negligible s. Because L u n d ' s observations were carried out in Wistar and Glaxo strains and ours in the Lewis strain we have repeated those experiments using the N a u t a technique. In the ipsilateral dorsal part of the lateral geniculate b o d y only few degenerated fibers were observed with prevalent location in its medial part. Some dispersed fibers were found in the ventral part o f the lateral geniculate body. Some degenerated axons in the optic stratum o f the superior colliculus were mainly located in its medial part and very few ones in the superficial grey layer. The contralateral distribution o f retinal fiber was in agreement with H a y h o w ' s description 6. Structures %r volumetric studies were chosen according to the terminal distribution o f retinofugal fibers. Clear-cut cytoarchitectural limitation o f each o f them was a necessary prerequisite for measuring. Although m a n y subcortical nuclei with retinal input have been described, the above criterion has considerably restricted their number. I n t h a l a m i e nuclei only the dorsal part of lateral geniculate b o d y ( G L D ) could be evaluated. Although the ventral part o f lateral geniculate b o d y is invaded by a number o f retinal fibers 6 it was not taken into account because o r its fusion with zona incerta. The volume o f the G L D ipsilateral to the lid-sutured eye was taken as 100 % (Table I). The decrease in volume o f the G L D contralateral to the lid-sutured TABLE I DIFFERENCEOF METRICVALUESBETWEENRIGHTAND LEFTVISUALCENTERSIN PERCENTAGES Metric values of visual centers of the right side corresponding to the open eye were taken as 100%. TO = tractus opticus; CS = colliculus superior; GLD = corpus geniculatum laterale pars dorsalis. Cortex
Experiment n = 18 Control n = 10
Subcortex
TO
I I - VI
II-IV
V- V1
GLD
CS
6.62 4- 1.48 -t = 4.47 0.52 + 1.14 t = 0.46
8.55 + 1.68 t = 5.08 1.39 4- 1.98 t = 0.71
5.07 + 2.27 t = 2.24 1.63 4- 1.20 t = 1.35
5.90 4- 1.01 t = 5.84 1.18 4- 3.24 t = 0.36
1.14 -q- 2.27 t = 0.50 0.24 4- 2.74 t = 0.09
0.53 i 1.13 t = 0.47 1.15 4- 2.88 t = 0.40
eye was 5.9 %. N o consistent difference could be determined in the thickness o f the stratum superficiale colliculi superioris. The depth o f the visual cortex from layer I I - V I and thickness o f layers I I - I V and V - V I were measured separately. The greatest difference was found in layer I I - I V : 8.6 %. N o a s y m m e t r y could be determined in the volume o f TO. Differences between the deprived and control side are summarized in Table I. The method of visual deprivation by lid closure was used in mice 1°, in kittensT,13,14, in rabbits, cats and dogs 1~. M a r k e d histological changes without signifiBrain Research, 6 (1967) 763-766
SHORT COMMUNICATIONS
765
cant alteration of metabolic activity in G L D layers fed by the deprived eye were shown by Wiesel and Hube113 and Kupfer and Palmer 7 in kittens having no previous visual experience. Using the same method in rats no such obvious differences in G L D structure were observed. However, when comparing the volumes of dorsal geniculate bodies receiving inputs from the covered and uncovered eye significant differences were obtained. Apparently species differences exist; the higher the subject's position in the phylogenetic scale, the greater its susceptibility to the experimental treatment. The relative importance of the amount of light reaching the retina through the occlusion follows from the extent of cell atrophy in cat, due to deprivation and deafferentation2,13. Moderate findings in monocular deprivation with translucent cover and the complete absence of changes when suturing the nictitating membrane across the cornea favor this assumption. In rats, where the lids are considerably thinner than in kittens, more intense retinal illumination could be expected. Thus our results could be compared with those obtained by translucent contact occluder in kittens la. By general observation Terry e t al. 1o were not able to demonstrate any difference between both G L D in mice with unilateral eye closure. The same was true for our material; only quantitative evaluation revealed the difference. We were not able to find any lateralized effect due to monocular closure in the CS, namely in the stratum griseum superficiale. Similarly, no changes were observed by Wiesel and Hubel la who did not mention, however, which part of CS was under study. The results of Umrath 12 and Gyllensten et al. 4 concern the stratum opticum and cannot be compared with ours for the stratum griseum superficiale. As half of the retinal fibers are distributed to the CSe, 11 the negative results are surprising enough. The non-visual input could be taken into account. The spinal, trigeminal and reticular afferents terminate mainly in deeper layers of CS so that their influence upon the upper layers would be indirect only. The most probable explanation of our negative results is the different nature of information transmitted to the CS and GLD. information about general level of illumination and its changes, which is necessary for unconditioned reactions, is not influenced by this kind o! deprivation. Significant decrease in volume of internuclear material in the optic stratum of CS in Gyllensten's 4 experiments with dark-reared mice supports this idea. Significant decrease in the thickness and cell density of the visual cortex with prevalence of changes in layers II-IV was observed 4.1~. Wiesel and Hube114 were not able to demonstrate obvious anatomical changes but profound physiological deficits in the visual area. It is mainly due to the binocular input of the majority of cortical cells. In rats, on the other hand, the effect of visual deprivation is lateralized due to the minimum of uncrossed fibers. The commissural fibers being distributed in the visual cortex very unequally, mainl~ in its lateral part a, do not disturb this laterality because our measurements were carried out in its medial part. This seems to be the reason why the closure of one eye has the same effect on the visual cortex and on the GLD. Greater differences in the thickness of layers II-IV as compared with layers V-VI are in agreement with terminal distribution of th~ optic radiation. Summing up: monocular lid closure causes significant decrease in the volume of the contralateral visual cortex and G L D but does not affect CS and TO. The Brain Research, 6 (1967) 763-766
766
SHORT COMMUNICATIONS
a b o v e results seem to indicate t h a t these changes are n o t degenerative in nature. T h e c o m p a r i s o n o f o u r d a t a with T s a n g ' s 11 results in enucleated rats (obvious v o l u m e decrease o f relevant G L D a n d CS with m o d e r a t e changes in the visual cortex) supp o r t s this a s s u m p t i o n . A l t h o u g h y o u n g a n i m a l s were used in o u r e x p e r i m e n t s we d o n o t s u p p o s e t h a t the described a s y m m e t r y is exclusively due to g r o w t h i n h i b i t i o n . U n e q u i v o c a l results were o b t a i n e d in G L D a n d CS a l t h o u g h the time courses o f m a t u r a t i o n o f diencephalic a n d mesencephalic structures are the same. G y l l e n s t e n ' s 4 finding o f decrease in the v o l u m e o f i n t e r n u c l e a r m a t e r i a l in visual cortex, G L D a n d CS in visually experienced d a r k - r e a r e d mice seems to j u s t i f y this conclusion. T h e a u t h o r w o u l d like to express her a p p r e c i a t i o n to Prof. R. Hassler for his help in the c y t o a r c h i t e c t o n i c d e t e r m i n a t i o n o f t h e visual cortex which was d o n e in the D e p a r t m e n t o f N e u r o a n a t o m y o f the M a x - P l a n c k - I n s t i t u t e in F r a n k f u r t / M . Institute of Physiology, Czechoslovak Academy of Sciences, Prague (Czechoslovakia)
E. FIFKOVA
1 BENNET,E. L., DIAMOND,M. C., KRECH, D., AND ROSENZWEIO,M. R., Chemical and anatomical plasticity of brain, Science, 146 (1964) 610-619. 2 COOK, W. H., WALTER,J. H., AND BAng, M. L., Cytological study of transneuronal atrophy in the cat and rabbit, J. comp. Neurol., 94 (1951) 267-292. 3 DIAMOND,M. C., KRECH, D., AND ROSEIqZWEIG,M. R., The effect of an enriched environment on the histology of rat cerebral cortex, J. comp. NeuroL, 123 (1964) 111-120. 4 GYLLENSTEN,L., MALMFORS,T., AND NORRLIN, M.-L., Effect of visual deprivation of the optic centers of growing and adult mice, J. comp. Neurol., 124 (1965) 149-160. 5 GYLLENSTEN,L., MALMFORS,T., AND NORRUN, M.-L., Growth alteration in the auditory cortex of visually deprived mice, J. comp. Neurol., 126 (1966) 463-470. 6 HAYHOW,W. R., SEFTON,A., AND WEBB, C., Primary optic centers of the rat in relation to the terminal distribution of the crossed and uncrossed optic nerve fibers, J. comp. Neurol., 118 (1962) 295-322. 7 KtrPFER, G., AND PALMER,P., Lateral geniculate nucleus: histological and cytochemical changes following afferent denervation and visual deprivation, Exp. Neurol., 9 (1964) 400-409. 8 LONO,R. D., Uncrossed visual pathways of hooded and albino rats, Science, 149 (1965) 1506-1507. 9 NAUTA,W. J. H., AND BUCHER, V. M., Efferent connections of the striate center in the albino rat, J. comp. Nearol., 100 (1954) 257-285. 10 TERRY,R.. J., ROLAND,A. L., AND RACE,J., Jr., Effect of eye enucleation and eyelid closure upon the brain and associated visual structures in the mouse, J. exp. Zool., 150 (1962) 165-184. 11 TSANG,J., Visual centers in blinded rats, J. comp. Neurol., 66 (1936) 211-262. 12 UMRATH,K., Histologische Ver~mderungen im Gehirn yon Tieren nach Ausschaltung yon Augen durch Verniihen der Lider oder durch Exstirpation,.~7. Biol., 115 (1965) 99-118. 13 WmSEL,T. N., AND HUBEL,D. H., Effects of visual deprivation on morphology and physiology of cells in the cat's lateral geniculate body, J. NeurophysioL, 26 (1963) 978-993. 14 WIESEL,T. N., AND HtJaEL, D. H., Single-cell responses in striate cortex of kittens deprived of vision in one eye, J. Neurophysiol., 26 (1963) 1003-1017. (Accepted September 27th, 1967)
Brain Research, 6 (1967) 763-766