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The effect of monocular exposure to temporal contrasts on ocular dominance in kittens
568
Brain Research, 134 (1977) 568-572 © Elsevier/North-Holland Biomedical Press
The effect of monocular exposure to temporal contrasts on ocular dominance in kittens
W. SINGER, J. RAUSCHECKER and R. WERTH
Max-Planck-lnstitut fiir Psychiatrie, Deutsche Forschungsanstalt ]iir Psychiatrie, 8000 Miinchen 40
(G.ER.) (Accepted May 25th, 1977)
It is now well established that monocular deprivation of spatial contrast vision leads to morphological and functional changes in the visual system of kittens when the unilateral eye closure is performed before or during a critical period in early postnatal life. In the visual cortex (VC) the percentage of cells excitable from the deprived eye decreases drasticallyl,~, 12. In the lateral geniculate nucleus (LGN) the laminae innervated from the deprived eye show a marked shrinkage and a reduction of average cell size z-4,10 whereby the degree of cell shrinkage parallels the amount of ocular dominance shiftL It is most commonly assumed that these effects are due to competition between afferents from the two eyes for synaptic sites at cortical neurones 3,a. But until now nothing is known about the mechanisms through which such competition might occur. One plausible hypothesis is that the differences in discharge patterns coming from the two eyes are responsible for the suppression c.f. for the consolidation of excitatory connections. The present experiments were designed to test whether mere asymmetry in afferent activity patterns is sufficient to account for the shift in ocular dominance or whether additional, more complex processes have to be assumed. For that purpose, three kittens from the same litter were raised in complete darkness until they were three weeks old. Subsequently they were exposed to flashing light which had an intensity of 1000 lux and was switched on and off every 1.5 sec. Background luminance was 2 lux. During exposure the left eye was covered with an opaque but fully translucent contact lens. This lens reliably suppressed vision of spatial contrasts but reduced light intensity only a negligible amount. The right eye was covered with a black contact lens over which the lids were closed with black adhesive tape. All kittens were exposed to these stimulation conditions for a total of 200 h, which were distributed over 6 weeks in daily sessions of 5-8 h. During exposure the kittens were kept together in a wooden box which was covered by an opaque perspex screen. They were permanently surveyed and entertained if necessary to prevent them from sleeping. During the free intervals they were kept together with their mother, again in complete darkness. The experiments were performed within the two weeks following the end of exposure. By that time the k~ttens' age was 10, 10.5 and 1 l weeks, respectively. For
569 the analysis o f o c u l a r d o m i n a n c e distributions the kittens were p r e p a r e d in the usual way s for single unit r e c o r d i n g in striate cortex. T h e y were p a r a l y z e d and k e p t u n d e r nitrous oxide anesthesia. T h e optics o f the a t r o p i n i z e d eyes were c o n t r o l l e d with a r e f r a c t o m e t e r a n d a f u n d u s c a m e r a a n d c o r r e c t e d with b l a c k c o n t a c t lenses c o n t a i n i n g artificial pupils o f 2 m m in diameter. Single unit recordings were o b t a i n e d with p o t a s sium-citrate filled m i c r o p i p e t t e s (impedances at 300 cps ranged f r o m 5 to 8 Mr2). T o further assess eventual global changes in the e x c i t a t o r y connections o f the two eyes, c o r t i c a l - e v o k e d potentials to flashes a n d to electrical s t i m u l a t i o n o f the optic nerves were analyzed in two kittens. F o r t h a t purpose, f o r k - s h a p e d electrical s t i m u l a t i o n electrodes were placed u n d e r visual c o n t r o l on the optic nerves within the orbita. T h e e v o k e d potentials were r e c o r d e d separately f r o m the two hemispheres between pairs o f silverball electrodes placed on striate cortex ( ( + ) - l e a d ) a n d suprasylvian gyrus ( ( - - ) - l e a d ) . T o d e t e r m i n e the effective a s y m m e t r y in the afferent activity f r o m the two eyes that had been achieved d u r i n g exposure, the stimulation conditions described a b o v e were repeated again at the beginning o f the r e c o r d i n g session. A s i n d i c a t e d in Fig. I A, the s t i m u l a t i o n c o n d i t i o n s d u r i n g exposure were highly a s y m m e t r i c for the two eyes.
B
A
on
t
off
, ,1
100msec
I
IO0/oV
!
i 10 r n s e c
Fig. 1. A: Cortical-evoked potentials (EPs) elicited by the light flashes to which the kittens had been exposed. 1. Right eye is covered with black contact lens and eyelid is closed with black adhesive tape, left eye is covered with opaque contact lens. 2. Both eyes are covered as right eye in 1. Contrast conditions in 1 and 2 are as during exposure (stimulus 1000 lux, background 2 lux). In 3 the eyes are closed as in 2 but contrast is increased by reduction of background luminance to 0.2 lux. Although all EPs are averaged from 200 stimulus presentations (repetition rate 1.5 sec) no response is distinguishable in conditions 2 and 3. B: cortical EPs following electrical stimulation of the optic nerves. 1 and 2 show the lesponses from the contralateral and 3 and 4 from the ipsilateral hemispheres after stimulation of the left and the right optic nerve, respectively. The crossed responses have larger amplitudes than the uncrossed responses, but in the corresponding combinations both nerves lead to responses of comparable amplitude. Stimulus strength is set twice above the saturation level of either nerve (50 #sec duration, 20 V). EPs are averaged from 50 responses.
570 With the contrast conditions maintained during exposure there was no flash-evoked potential when the eyes were covered in the way the right eye was closed during exposure. This was true even when background luminance was further reduced to 0.2 lux. But there was a large response both at on- and offset of stimulation when one eye was covered only with the opaque lens. The evaluation of cortical responses elicited by electrical stimulation of the optic nerves showed no asymmetry between the two eyes (Fig. 1B). The response in the respective contralateral hemispheres was always slightly larger than on the ipsilateral side but both nerves seemed equally effective. To assess the efficiency of binocular inhibitory interactions one nerve was stimulated 20 msec prior to the other. This indicated that also binocular inhibition was equally well elicited from either nerve; but again the inhibition of the ipsilateral response by conditioning stimulation of the contralateral nerve was stronger than the inhibition after reversed stimulus conditions. The single unit analysis fully confirmed the evoked potential data. All cells recorded had their receptive fields (RF) within 8° from the area centralis. Out of the 184 cells analyzed, 83 units were from the right and 101 cells from the left hemispheres. In spite of the fact that the kittens were deprived from contour vision, a surprisingly high percentage (89.7 ~o) of the cells could be driven with hand-held light stimuli, and these percentages were similar in the two hemispheres (88.0 ~,~ in the right and 91.1 ~ in the left hemispheres). But the responses were only rarely as vigorous as in cats raised with normal vision. As expected, the selectivity for stimulus orientation and direction was considerably lower than in fully experienced kittens of the same age (see Table I). Out of 120 cells which could be thoroughly tested for orientation selectivity, 4 9 ~ showed no preference for a particular stimulus orientation. Only 1.6 ~o of the cells with orientation preference were as sharply tuned as cells in normal cortex (reactive within ± 20 ° of the optimal orientation). The majority of cells with oriented RFs (70 ~ ) only showed orientational bias and reacted within a range of ~z 40 ° to _~ 80 ° of the optimal orientation. In this respect there was no statistically significant difference between cells excited preferentially from the left or the righ~ eye. Contrasting the conditions in non-deprived animals, numerous cells would also respond to large non-structured stationary flashed stimuli. These properties of the receptive fields can be taken as further guarantee that the animals had no uncontrolled visual experience. in spite of the raising conditions, however, the ocular dominance distribution was symmetrical and similar to that found in normal adult cats. Ocular dominance TABLE 1 Orientation tuning
Percentage o f ceils (n ~ leO)
below ± 2if' -/- 20°~0 '~ :~ 40o-60° ~z 60o-80° no orientation preference
0.83 14.17 17.50 18.33 49.17
571 was rated in 5 categories and determined for 142 neurons. The pooled data from neurons in both hemispheres of all three cats are shown in Fig. 2A. The large majority (41 ~ ) of cells are equally well driven from either eye and only a small fraction of cells is exclusively driven from either the left (10 ~ ) or the right (9 ~ ) eye. Neither these pooled data nor the individual results of the three kittens provide any evidence for a disruption of binocularity or a shift in ocular dominance towards the stimulated left eye. Unlike in cats in which binocularity has been interfered with (unpublished observations) there was also no obvious preference for the respective contralateral eye. When ocular dominance was rated in the classical ipsi-contra scale, the distribution still remained by and large symmetrical with a slight preponderance of the ipsilateral eye (Fig. 2B). Three neurons rated in ocular dominance class 3 (equally well responsive to either eye) were tested for binocular summation and all 3 cells gave more vigorous responses when both eyes were stimulated simultaneously. In normal cats, monosynaptically driven simple cells in layer IV are generally more sharply tuned and more often dominated by only one eye than complex cells which are more remote from retinal input 6. This trend was apparent also in the present set of data. Cells with extremely broad tuning (above ± 60 °) or non-oriented fields were relatively more frequent in ocular dominance class 3 (71.1%) than in classes 1 and 2 (37.5 %) and in classes 4 and 5 (33.3 ~). Tested with Z~ this difference was significant beyond the P ~< 0.001 level. The few sharply tuned ceils were eventually distributed over all ocular dominance classes. But because these cells as well as the purely monocular cells were so infrequent, this latter observation should not be generalized. In conclusion, the present results indicate that mere asymmetry in the temporal modulation of afferent activity from the two eyes is not sufficient to disrupt the binocularity or to change the ocular dominance of cortical neurons. It can be inferred from so~-
A
so~
B
n=142
r;~t 1
2
3
4
n=142
5 lef~
contralat leye
2
;
4
5 ,ps,lateye
Fig. 2. Ocular dominance distributions calculated from the pooled data of all three kittens. In A ocular dominance is evaluated for the right and the left eye, in B the distlibution is shown for the respective contra- and ipsJ|ateral eye. Classes 1 and 5 correspond to cells excitable from only one eye. Classes 2 and 4 contain cells that are excitable from both eyes but dominated from one eye. Cells that are equally well driven from either eye are grouped in class 3. The distributions in A and B show no disruption o f binocularity, nor do they indicate a shift in ocular dominance to the left eye or to the respective contralateral eye.
572 the cortical potentials e v o k e d by the flashing light that such a s y m m e t r y had been assured by the exposure conditions. S t i m u l a t i o n h a d certainly led to g r o u p e d discharges a n d p r o b a b l y also to an overall increase o f activity in the afferents from the left eye while the afferents from the right eye were only s p o n t a n e o u s l y active. It can further be assumed t h a t this a s y m m e t r y had been m a i n t a i n e d long e n o u g h to p r o d u c e changes in cortical connectivity since changes in ocular d o m i n a n c e are consistently seen after m u c h shorter exposure times with c o n v e n t i o n a l m o n o c u l a r d e p r i v a t i o n 1. Thus, other factors t h a n mere differences in b i n o c u l a r activity have to be p o s t u l a t e d as prerequisite for changes in ocular d o m i n a n c e . The experiments described in the following p a p e r o f this volume a are designed to further delineate these parameters. In a d d i t i o n to this m a i n conclusion, it is n o t e w o r t h y that the percentage o f lightreactive cells in the present p r e p a r a t i o n was considerably higher t h a n that f o u n d in cats with p r o l o n g e d b i n o c u l a r d e p r i v a t i o n 7,12. In a previous investigation o f one-yearold binocularly deprived cats, in which precisely the same recording techniques h a d been applied, only 33 ~o o f the cells were still reactive to light stimuli 7. Possible exp l a n a t i o n s are: (1) that d i s r u p t i o n o f the excitatory connections cocltinues b e y o n d the 1 l t h week when d e p r i v a t i o n is p r o l o n g e d or (2) that t e m p o r a l m o d u l a t i o n o f retinal activity can m a i n t a i n excitatory connections even t h o u g h it does n o t alter ocular d o minance.
1 Blakemore, C. and van Sluyters, R. C., Reversal of the physiological effects of monocular deprivation in kittens: further evidence for a sensitive period, J. PhysioL (Lond.), 237 (1974) 195-216. 2 Dfirsteler, M. R., Garey, L. J. and Movshon, J. A., Reversal of the morphological effects of monocular deprivation in the kitten's lateral geniculate nucleus, J. Physiol. (Lond.), 261 (1976) 189-210. 3 Guillery, R. W., Binocular competition in the control of geniculate cell growth, J. comp. Neurol., 144 (1972) 117-127. 4 GuiUery, R. W. and Stelzner, D. J., The differential effects of unilateral lid closure upon the monocular and binocular segments of the dorsal lateral geniculate nucleus in the cat, J. comp. Neurol., 139 (1970) 413-422. 5 Hubel, D. H. and Wiesel, T. N., The period of susceptibility to the physiologicaleffects of unilateral eye closure in kittens, J. PhysioL (Lond.), 206 (1970) 419436. 6 Singer, W., Cynader, M. and Tretter, F., On the organization of cat striate cortex ; a correlation of receptive field properties with afferent and efferent connections, J. Neurophysiol., 38 (1975) 10801098. 7 Singer, W. and Tretter, F., Receptive field properties and neuronal connectivity in the striate and parastriate cortex of contour deplived cats, J. Neuropkysiol., 39 (1976) 613-630. 8 Singer, W. and Tretter, F., Unusually large receptive fields in cats with restricted visual experience, Exp. Brain Res., 26 (1976) 171-184. 9 Singer, W., Yinon, U. and Trettet, F., Rotation of the open eye in monocularly deprived kittens prevents ocular dominance shift, Brain Research, in preparation, 10 Wiesel, T. N. and Hubel, D. H., Effects of visual deprivation on morphology and physiology of ceils in the cat's lateral geniculate body, J. Neurophysiol., 26 (1963) 978-993. I 1 Wiesel, T. N. and Hubel, D. H., Single-cell response in striate cortex of kitteos deprived of vision in one eye, J. NeurophysioL, 26 (1963) 1003-1017. 12 Wiesel, T. N. and Hubel, D. H., Comparison of the effects of unilateral and bilateral eye closure on cortical unit responses in kittens, J. Neurophysiol., 28 (1965) 1029-1040.
Brain Research, 134 (1977) 568-572 © Elsevier/North-Holland Biomedical Press
The effect of monocular exposure to temporal contrasts on ocular dominance in kittens
W. SINGER, J. RAUSCHECKER and R. WERTH
Max-Planck-lnstitut fiir Psychiatrie, Deutsche Forschungsanstalt ]iir Psychiatrie, 8000 Miinchen 40
(G.ER.) (Accepted May 25th, 1977)
It is now well established that monocular deprivation of spatial contrast vision leads to morphological and functional changes in the visual system of kittens when the unilateral eye closure is performed before or during a critical period in early postnatal life. In the visual cortex (VC) the percentage of cells excitable from the deprived eye decreases drasticallyl,~, 12. In the lateral geniculate nucleus (LGN) the laminae innervated from the deprived eye show a marked shrinkage and a reduction of average cell size z-4,10 whereby the degree of cell shrinkage parallels the amount of ocular dominance shiftL It is most commonly assumed that these effects are due to competition between afferents from the two eyes for synaptic sites at cortical neurones 3,a. But until now nothing is known about the mechanisms through which such competition might occur. One plausible hypothesis is that the differences in discharge patterns coming from the two eyes are responsible for the suppression c.f. for the consolidation of excitatory connections. The present experiments were designed to test whether mere asymmetry in afferent activity patterns is sufficient to account for the shift in ocular dominance or whether additional, more complex processes have to be assumed. For that purpose, three kittens from the same litter were raised in complete darkness until they were three weeks old. Subsequently they were exposed to flashing light which had an intensity of 1000 lux and was switched on and off every 1.5 sec. Background luminance was 2 lux. During exposure the left eye was covered with an opaque but fully translucent contact lens. This lens reliably suppressed vision of spatial contrasts but reduced light intensity only a negligible amount. The right eye was covered with a black contact lens over which the lids were closed with black adhesive tape. All kittens were exposed to these stimulation conditions for a total of 200 h, which were distributed over 6 weeks in daily sessions of 5-8 h. During exposure the kittens were kept together in a wooden box which was covered by an opaque perspex screen. They were permanently surveyed and entertained if necessary to prevent them from sleeping. During the free intervals they were kept together with their mother, again in complete darkness. The experiments were performed within the two weeks following the end of exposure. By that time the k~ttens' age was 10, 10.5 and 1 l weeks, respectively. For
569 the analysis o f o c u l a r d o m i n a n c e distributions the kittens were p r e p a r e d in the usual way s for single unit r e c o r d i n g in striate cortex. T h e y were p a r a l y z e d and k e p t u n d e r nitrous oxide anesthesia. T h e optics o f the a t r o p i n i z e d eyes were c o n t r o l l e d with a r e f r a c t o m e t e r a n d a f u n d u s c a m e r a a n d c o r r e c t e d with b l a c k c o n t a c t lenses c o n t a i n i n g artificial pupils o f 2 m m in diameter. Single unit recordings were o b t a i n e d with p o t a s sium-citrate filled m i c r o p i p e t t e s (impedances at 300 cps ranged f r o m 5 to 8 Mr2). T o further assess eventual global changes in the e x c i t a t o r y connections o f the two eyes, c o r t i c a l - e v o k e d potentials to flashes a n d to electrical s t i m u l a t i o n o f the optic nerves were analyzed in two kittens. F o r t h a t purpose, f o r k - s h a p e d electrical s t i m u l a t i o n electrodes were placed u n d e r visual c o n t r o l on the optic nerves within the orbita. T h e e v o k e d potentials were r e c o r d e d separately f r o m the two hemispheres between pairs o f silverball electrodes placed on striate cortex ( ( + ) - l e a d ) a n d suprasylvian gyrus ( ( - - ) - l e a d ) . T o d e t e r m i n e the effective a s y m m e t r y in the afferent activity f r o m the two eyes that had been achieved d u r i n g exposure, the stimulation conditions described a b o v e were repeated again at the beginning o f the r e c o r d i n g session. A s i n d i c a t e d in Fig. I A, the s t i m u l a t i o n c o n d i t i o n s d u r i n g exposure were highly a s y m m e t r i c for the two eyes.
B
A
on
t
off
, ,1
100msec
I
IO0/oV
!
i 10 r n s e c
Fig. 1. A: Cortical-evoked potentials (EPs) elicited by the light flashes to which the kittens had been exposed. 1. Right eye is covered with black contact lens and eyelid is closed with black adhesive tape, left eye is covered with opaque contact lens. 2. Both eyes are covered as right eye in 1. Contrast conditions in 1 and 2 are as during exposure (stimulus 1000 lux, background 2 lux). In 3 the eyes are closed as in 2 but contrast is increased by reduction of background luminance to 0.2 lux. Although all EPs are averaged from 200 stimulus presentations (repetition rate 1.5 sec) no response is distinguishable in conditions 2 and 3. B: cortical EPs following electrical stimulation of the optic nerves. 1 and 2 show the lesponses from the contralateral and 3 and 4 from the ipsilateral hemispheres after stimulation of the left and the right optic nerve, respectively. The crossed responses have larger amplitudes than the uncrossed responses, but in the corresponding combinations both nerves lead to responses of comparable amplitude. Stimulus strength is set twice above the saturation level of either nerve (50 #sec duration, 20 V). EPs are averaged from 50 responses.
570 With the contrast conditions maintained during exposure there was no flash-evoked potential when the eyes were covered in the way the right eye was closed during exposure. This was true even when background luminance was further reduced to 0.2 lux. But there was a large response both at on- and offset of stimulation when one eye was covered only with the opaque lens. The evaluation of cortical responses elicited by electrical stimulation of the optic nerves showed no asymmetry between the two eyes (Fig. 1B). The response in the respective contralateral hemispheres was always slightly larger than on the ipsilateral side but both nerves seemed equally effective. To assess the efficiency of binocular inhibitory interactions one nerve was stimulated 20 msec prior to the other. This indicated that also binocular inhibition was equally well elicited from either nerve; but again the inhibition of the ipsilateral response by conditioning stimulation of the contralateral nerve was stronger than the inhibition after reversed stimulus conditions. The single unit analysis fully confirmed the evoked potential data. All cells recorded had their receptive fields (RF) within 8° from the area centralis. Out of the 184 cells analyzed, 83 units were from the right and 101 cells from the left hemispheres. In spite of the fact that the kittens were deprived from contour vision, a surprisingly high percentage (89.7 ~o) of the cells could be driven with hand-held light stimuli, and these percentages were similar in the two hemispheres (88.0 ~,~ in the right and 91.1 ~ in the left hemispheres). But the responses were only rarely as vigorous as in cats raised with normal vision. As expected, the selectivity for stimulus orientation and direction was considerably lower than in fully experienced kittens of the same age (see Table I). Out of 120 cells which could be thoroughly tested for orientation selectivity, 4 9 ~ showed no preference for a particular stimulus orientation. Only 1.6 ~o of the cells with orientation preference were as sharply tuned as cells in normal cortex (reactive within ± 20 ° of the optimal orientation). The majority of cells with oriented RFs (70 ~ ) only showed orientational bias and reacted within a range of ~z 40 ° to _~ 80 ° of the optimal orientation. In this respect there was no statistically significant difference between cells excited preferentially from the left or the righ~ eye. Contrasting the conditions in non-deprived animals, numerous cells would also respond to large non-structured stationary flashed stimuli. These properties of the receptive fields can be taken as further guarantee that the animals had no uncontrolled visual experience. in spite of the raising conditions, however, the ocular dominance distribution was symmetrical and similar to that found in normal adult cats. Ocular dominance TABLE 1 Orientation tuning
Percentage o f ceils (n ~ leO)
below ± 2if' -/- 20°~0 '~ :~ 40o-60° ~z 60o-80° no orientation preference
0.83 14.17 17.50 18.33 49.17
571 was rated in 5 categories and determined for 142 neurons. The pooled data from neurons in both hemispheres of all three cats are shown in Fig. 2A. The large majority (41 ~ ) of cells are equally well driven from either eye and only a small fraction of cells is exclusively driven from either the left (10 ~ ) or the right (9 ~ ) eye. Neither these pooled data nor the individual results of the three kittens provide any evidence for a disruption of binocularity or a shift in ocular dominance towards the stimulated left eye. Unlike in cats in which binocularity has been interfered with (unpublished observations) there was also no obvious preference for the respective contralateral eye. When ocular dominance was rated in the classical ipsi-contra scale, the distribution still remained by and large symmetrical with a slight preponderance of the ipsilateral eye (Fig. 2B). Three neurons rated in ocular dominance class 3 (equally well responsive to either eye) were tested for binocular summation and all 3 cells gave more vigorous responses when both eyes were stimulated simultaneously. In normal cats, monosynaptically driven simple cells in layer IV are generally more sharply tuned and more often dominated by only one eye than complex cells which are more remote from retinal input 6. This trend was apparent also in the present set of data. Cells with extremely broad tuning (above ± 60 °) or non-oriented fields were relatively more frequent in ocular dominance class 3 (71.1%) than in classes 1 and 2 (37.5 %) and in classes 4 and 5 (33.3 ~). Tested with Z~ this difference was significant beyond the P ~< 0.001 level. The few sharply tuned ceils were eventually distributed over all ocular dominance classes. But because these cells as well as the purely monocular cells were so infrequent, this latter observation should not be generalized. In conclusion, the present results indicate that mere asymmetry in the temporal modulation of afferent activity from the two eyes is not sufficient to disrupt the binocularity or to change the ocular dominance of cortical neurons. It can be inferred from so~-
A
so~
B
n=142
r;~t 1
2
3
4
n=142
5 lef~
contralat leye
2
;
4
5 ,ps,lateye
Fig. 2. Ocular dominance distributions calculated from the pooled data of all three kittens. In A ocular dominance is evaluated for the right and the left eye, in B the distlibution is shown for the respective contra- and ipsJ|ateral eye. Classes 1 and 5 correspond to cells excitable from only one eye. Classes 2 and 4 contain cells that are excitable from both eyes but dominated from one eye. Cells that are equally well driven from either eye are grouped in class 3. The distributions in A and B show no disruption o f binocularity, nor do they indicate a shift in ocular dominance to the left eye or to the respective contralateral eye.
572 the cortical potentials e v o k e d by the flashing light that such a s y m m e t r y had been assured by the exposure conditions. S t i m u l a t i o n h a d certainly led to g r o u p e d discharges a n d p r o b a b l y also to an overall increase o f activity in the afferents from the left eye while the afferents from the right eye were only s p o n t a n e o u s l y active. It can further be assumed t h a t this a s y m m e t r y had been m a i n t a i n e d long e n o u g h to p r o d u c e changes in cortical connectivity since changes in ocular d o m i n a n c e are consistently seen after m u c h shorter exposure times with c o n v e n t i o n a l m o n o c u l a r d e p r i v a t i o n 1. Thus, other factors t h a n mere differences in b i n o c u l a r activity have to be p o s t u l a t e d as prerequisite for changes in ocular d o m i n a n c e . The experiments described in the following p a p e r o f this volume a are designed to further delineate these parameters. In a d d i t i o n to this m a i n conclusion, it is n o t e w o r t h y that the percentage o f lightreactive cells in the present p r e p a r a t i o n was considerably higher t h a n that f o u n d in cats with p r o l o n g e d b i n o c u l a r d e p r i v a t i o n 7,12. In a previous investigation o f one-yearold binocularly deprived cats, in which precisely the same recording techniques h a d been applied, only 33 ~o o f the cells were still reactive to light stimuli 7. Possible exp l a n a t i o n s are: (1) that d i s r u p t i o n o f the excitatory connections cocltinues b e y o n d the 1 l t h week when d e p r i v a t i o n is p r o l o n g e d or (2) that t e m p o r a l m o d u l a t i o n o f retinal activity can m a i n t a i n excitatory connections even t h o u g h it does n o t alter ocular d o minance.
1 Blakemore, C. and van Sluyters, R. C., Reversal of the physiological effects of monocular deprivation in kittens: further evidence for a sensitive period, J. PhysioL (Lond.), 237 (1974) 195-216. 2 Dfirsteler, M. R., Garey, L. J. and Movshon, J. A., Reversal of the morphological effects of monocular deprivation in the kitten's lateral geniculate nucleus, J. Physiol. (Lond.), 261 (1976) 189-210. 3 Guillery, R. W., Binocular competition in the control of geniculate cell growth, J. comp. Neurol., 144 (1972) 117-127. 4 GuiUery, R. W. and Stelzner, D. J., The differential effects of unilateral lid closure upon the monocular and binocular segments of the dorsal lateral geniculate nucleus in the cat, J. comp. Neurol., 139 (1970) 413-422. 5 Hubel, D. H. and Wiesel, T. N., The period of susceptibility to the physiologicaleffects of unilateral eye closure in kittens, J. PhysioL (Lond.), 206 (1970) 419436. 6 Singer, W., Cynader, M. and Tretter, F., On the organization of cat striate cortex ; a correlation of receptive field properties with afferent and efferent connections, J. Neurophysiol., 38 (1975) 10801098. 7 Singer, W. and Tretter, F., Receptive field properties and neuronal connectivity in the striate and parastriate cortex of contour deplived cats, J. Neuropkysiol., 39 (1976) 613-630. 8 Singer, W. and Tretter, F., Unusually large receptive fields in cats with restricted visual experience, Exp. Brain Res., 26 (1976) 171-184. 9 Singer, W., Yinon, U. and Trettet, F., Rotation of the open eye in monocularly deprived kittens prevents ocular dominance shift, Brain Research, in preparation, 10 Wiesel, T. N. and Hubel, D. H., Effects of visual deprivation on morphology and physiology of ceils in the cat's lateral geniculate body, J. Neurophysiol., 26 (1963) 978-993. I 1 Wiesel, T. N. and Hubel, D. H., Single-cell response in striate cortex of kitteos deprived of vision in one eye, J. NeurophysioL, 26 (1963) 1003-1017. 12 Wiesel, T. N. and Hubel, D. H., Comparison of the effects of unilateral and bilateral eye closure on cortical unit responses in kittens, J. Neurophysiol., 28 (1965) 1029-1040.