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Analysis of monocular optokinetic nystagmus in normal and visually deprived kittens
Brain Research, 210 (1981) 367-372 © Elsevier/North-Holland Biomedical Press
367
Analysis of monocular optokinetic nystagmus in normal and visually deprived kittens
RAFI MALACH, NICK STRONG and RICHARD C. VAN SLUYTERS* School of Optometry, University of California, Berkeley, Cali.[~ 94720 (U.S.A.) (Accepted November 6th, 1980) Key words: optokinetic nystagmus - - kitten - - visual deprivation
The asymmetry of monocular OKN was assessed in normal, monocularly deprived (nondeprived eye) and strabismic cats. No significant differences were observed between the responses of these 3 groups. In young kittens, the gain of OKN for nasalward stimulus movement was larger than that for temporalward. This asymmetry declined to a low residual level by about one year of age. Neurophysiological recordings indicated that the symmetry of OKN is not related to cortical binocularity. Cats reared from birth with one eye sutured dosed suffer marked deficits in their visual capacities, and in the response properties of their visual neurons, when tested through that eye later in life. Recently, it was reported that monocularly deprived (MD) cats also may manifest abnormal visuomotor behavior when tested through the non-deprived eye. Optokinetic nystagmus ( O K N ) elicited by stimuli moving from nasal-to-temporal in the visual field of this eye (T-OKN) was 'irregular' or even 'negative,' while O K N in response to temporal-to-nasal movement (N-OKN) was 'regular'S. Current evidence suggests that, in the cat, T - O K N is dependent upon descending cortico-pretectal pathways, while N - O K N can be mediated by direct retino-pretectal connections2,3,14. Since prolonged periods of M D are known to cause a sharp decrease in cortical binocularity lz, it was suggested that abnormal O K N responses through the non-deprived eye were a result of this loss of binocularity 10. This raised the intriguing possibility that normal development of the descending cortical-pretectal pathways subserving the non-deprived eye was in some way dependent upon the presence of a balanced level of competitive interaction between afferent sensory pathways from the two eyes early in life. However, M D is not the most suitable preparation for studying the role of cortical binocularity in O K N since, in addition to losing binocular cells, M D cats also undergo a massive shift in cortical ocular dominance so that few cells retain functional connections with the deprived eye6,13. There is also the possibility that preventing *To whom correspondence should be addressed.
368 pattern vision neonatally may hinder normal development of the direct retinopretectal pathways involved in O K N ~. To clarify this situation, we have studied monocular O K N in normal cats, MD cats and cats reared with divergent strabismus - - a procedure known to cause a loss of cortical binocularity that is not associated with a shift in ocular dominance 5,1'. All of the techniques and procedures used to rear animals, impose visual deprivation and record from single units in the visual cortex are described in detail elsewhere11,1'. In the present study, M D (eyelid suture) or divergent strabismus (medial rectus tenotomy) was induced within a week of natural eye opening. Monocular O K N was recorded from hand-held animals positioned at the center of a large drum (112 cm diameter × 117 cm high). The drum was rotated at velocities ranging from 4 ° to 50°/sec. The inner surface of the drum was covered with one of two repetitive, high-contrast (86 °/o, background luminance -: 6 cdm -2) patterns. These patterns consisted of either dark vertical stripes whose width was 10', or a random array of dark spots whose diameters ranged from 0.6 ° to 10°. No consistent differences were observed in the O K N elicited by these two patterns, and most of the data reporMONOCULARLY DEPRIVED
NORMAL
1 mY
STRAB I S M I C
2 sec
2O AREA 17 In -.I ..J
N = 3"3
N= 3
N= 32
10
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,,0
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1 2 3 4 5 6 7
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N=32
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234
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N=30
67
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34
6
N= 31
6
7
1
234
56
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VU
DOMINANCE
Fig. 1. Monocular O K N and cortical ocular dominance in normal, MD and strabismic cats. Data shown in the left-hand column are from a 6-month-old normal cat (K666), those in the middle column are from a cat monocularly deprived from near birth to 4 years of age (K146) and those in the righthand column are from a cat given a divergent strabismus neonatally and studied at 6 months of age (K619). For all the O K N responses, stimulus velocity was 24°/sec and eye movements to the left are indicated by an upward deflection of the record. Cortical units were classified into one of seven ocular dominance groups according to the criteria of Hubel and Wiesel4. Arrows indicate units dominated by the deprived eye of the MD cat. Top row, N - O K N responses; second row, T-OKN responses; third row, ocular dominance histograms for area 17; and bottom row, ocular dominance histograms for area 18.
369 ted here were obtained with the spot array. Eye movements were recorded using DClinked, bitemporal, EOG skin electrodes (In Vivo Metric). In many cats, single units were recorded from striate and parastriate cortex (areas 17 and 18, respectively) at the conclusion of these O K N measurements. When normally reared cats or cats subjected to prolonged periods of either M D or strabismus were placed in the drum, it immediately became apparent that vigorous and regular T - O K N could be elicited by stimulating either eye of the normal and the strabismic cats, or by stimulating the non-deprived eye of the M D cats. Samples of the O K N records for a normal cat and for two of the cats exposed to prolonged periods of deprivation are shown in Fig. 1, together with the ocular dominance histograms obtained for ceils recorded from areas 17 and 18 in these cats. There is no obvious impairment of T - O K N relative to N - O K N in either the M D cat or the strabismic cat despite the virtual absence of cortical binocular cells in each of these cats. Our initial qualitative impressions were born out by subsequent quantitative analysis of the O K N data. This was accomplished by calculating an 'asymmetry index' (AI) for each cat, which is given by: vt AI ----- 1 - - Vn where Vt is the T - O K N slow-phase velocity and Vn is the N - O K N slow-phase velocity. An AI of 0.0 indicates equal O K N gain in both directions (no asymmetry) and an AI of 1.0 indicates total loss of T - O K N (maximum asymmetry). The AI values for the 3
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Fig. 2. Asymmetryof monocular OKN during development. An index of the asymmetryin monocular OKN responses was calculated for each recording session in 44cats of various ages (see text for details). To .qualifyfor this form of analysis, an eye movementrecord for a givenstimulus velocityhad to contain a minimum of 10 consecutiveOKN beats for cats over 4 months of age, and 5 consecutivebeats for cats younger than 4 months. All the data presented in this figure were collected using a stimulus velocityof 24°/see. The asymmetry index is plotted as a function of the ago at recording (log scale) for normal (unfilled circles, n = 23), MD (non-deprived eyes only, filled circles, n = 17) and strabismic (crosses, n = 4) cats. Points connected by lines represent data collected from the same eye at different ages (see text). Upward and downward pointing arrows indicate pairs of points representing data collectedfrom both eyes of the same cat (either normal or strabismic) during a single recording session.
370 cats in Fig. 1 were 0.37, 0.24 and 0.18 for the normal, M D and strabismic cats, respectively. Although we failed to find any significant increase in the asymmetry of monocular O K N responses from animals subjected to prolonged periods of deprivation, it was still conceivable that deprivation differentially affected the rate of development of T and N - O K N in kittens. To examine this possibility, we studied the development of monocular O K N in normal and visually deprived kittens. Early in this project we found, as has been described by others 1,7, that the vigor of O K N rapidly declines with repeated testing. Therefore, it was decided to conduct a cross-sectional study of monocular O K N in a large sample of kittens of various ages, as a first step toward studying the development of O K N . Recording was limited in each kitten to just a few sessions separated by at least 3 weeks. The results of this cross-sectional study of 44 cats are given in Fig. 2, where the asymmetry index is plotted as a function of the age at recording for normal, M D and strabismic kittens. Inspection of this figure reveals that the O K N responses obtained from young M D or strabismic kittens can exhibit marked asymmetry, both in terms of the gain and the regularity of the response. However, this asymmetry is not a consistent finding in visually deprived kittens of a given age, and, more importantly, normal kittens of the same age often produced equally asymmetric responses. These data from developing kittens are obviously quite variable, but there is an unmistakable trend toward reduced asymmetry with increasing age regardless of the rearing paradigm employed. While all the data presented in Fig. 2 were obtained using a stimulus velocity of 24°/sec, there were also no consistent differences between these 3 groups of animals when stimulus velocities ranging from 4 ° to 50°/sec were employed. The data presented here fail to confirm those of van Hof-van Duin 8, who found deficient T - O K N in the non-deprived eye of cats subjected to prolonged M D from birth. We find no evidence of a consistent difference at any age, when the monocular O K N responses of M D kittens are compared to those of normal kittens. We do find marked asymmetries in some deprived kittens (see Fig. 2), but normal kittens of the same age can exhibit equally large asymmetries. A possible source of some of the discrepancy between these two studies might be differences in the methods used to assess eye movements. First, van H o f - v a n Duin chose to use direct observation of the eyes to evaluate O K N responses in hand-held animals rather than the DC-linked EOG signals that were employed in the present study. A second possibility stems from differences in the frequency with which animals were subjected to O K N recording. Whereas van H o f - v a n Duin studied O K N extensively in each cat 8, recording from the same cat as often as once a day 9, we limited recording to very few sessions (often only one with each cat), separated by long intervals, and sampled across a large number of cats. It may be that normal and visually deprived cats differ in terms of the rate of habituation of their T - O K N responses - - a question we are currently investigating. We found no evidence of T - O K N specific deficits in several cats reared with prolonged periods of either M D or strabismus - - two conditions known to produce a marked reduction in cortical binocularity. However, even if M D did cause changes in
371 T - O K N responses for the non-deprived eye of some cats, these deficits could not be due solely to changes in cortical binocularity since prolonged M D always causes a dramatic decrease in the proportion of cortical binocular neurons. An example of this lack of correlation is demonstrated by our results from cats exposed to prolonged periods of MD or divergent strabismus. In these animals, cortical binocularity was reduced severely (see Fig. 1), but T - O K N was not selectively depressed. It is possible that there is some other, less reliable, neurophysiological consequence of MD that can cause altered T - O K N through the non-deprived eye. For example, Hoffmann 2 has reported that MD can cause a loss of ipsilateral input to the nucleus of the optic tract (a pretectal center thought to mediate horizontal OKN) bilaterally. However, since monocular O K N responses were not assessed in these cats and no data were presented regarding the reliability of this neural loss, it is difficult to evaluate the functional significance of this finding. Our analysis of the development of monocular O K N in normal kittens (see Fig. 2) confirms and extends van Hof-van Duin's 10 observation that N - O K N appears earlier than T-OKN. It is important to realize how slowly T-OKN matures. In most kittens, monocular O K N responses are quite asymmetric until around 10 weeks of age. This is interesting in view of the suggestion that N - O K N can be mediated by direct retino-pretectal pathways but that T-OKN is dependent upon an indirect corticopretectal input ~4. It would be misleading to leave the impression that prolonged MD fails to alter monocular O K N in the cat. In this paper we have presented only those data related to performance through the non-deprived eye. We have found marked changes in O K N performance in a preliminary experiment where stimuli were presented to the deprived eye alone. We are currently studying the role of functional deficits in the retinothalamo-cortical pathways in producing these changes. We are grateful for assistance from M. Stone and G. Fuller in recording eye movements, F. Levitt in recording single units, R. Huppenbauer in reconstructing electrode tracks and C. Nicholson in typing and editing the manuscript. This research was supported partially by a research fellowship from the Alfred P. Sloan Foundation, a research grant from the National Institutes of Health (EY 02193) and a National Institutes of Health Biomedical Sciences Research Grant (RR 07006) awarded to R.C.V.S.
1 Braun, J. J. and Gault, F. P., Monocular and binocular control of horizontal optokinetic nystagmus in cats and rabbits, J. comp. physiol. Psychol., 69 (1969) 12-16. 2 Hoffmann, K.-P., Optokinetic nystagmus and single-cellresponses in the nucleus tractus opticus after early monocular deprivation in the cat. In R. D. Freeman (Ed.), Developmental Neurobiology of Vision, Plenum Press, New York, N.Y., 1979, pp. 63-72. 3 Hoffmann, K.-P. and Schoppmann, A., Retinal input to direction selective cells in the nucleus opticus tractus of the cat, Brain Research, 99 (1975) 359-366. 4 Hubel, D. H. and Wiesel, T. N., Receptive fields, binocular interaction and functional architecture in the cat's visual cortex, J. Physiol. (Lond.), 165 (1962) 559-568.
372 5 Hubel, D. H. and Wiesel, T. N., Binocular interaction in striate cortex of kittens reared with artificial squint, J. Neurophysiol., 28 (1965) 1041-1059. 6 Shatz, C. J. and Stryker, M. P., Ocular dominance in Layer IV of the cat's visual cortex and the effects of monocular deprivation, J. Physiol. ~Lond.), 281 (1978) 267-283. 7 Stryker, M. and Blakemore, C., Saccadic and disjunctive eye movements in cats, Vision Res., 12 (1972) 2005-2013. 8 van Hof-van Duin, J., Early and permanent effects of monocular deprivation on pattern discrimination and visuomotor behavior in cats, Brain Research, 111 (1976) 261-276. 9 van Hof-van Duin, J., Asymmetry of Optokinetic Nystagmus Observed in Normal Kittens and Light Deprived Cats. In G. Kommerell (Ed.), Disorders of Ocular Motility, J. F. Bergmann Verlag, Mfinchen, 1978, pp. 363-366. 10 van Hof-van Duin, J., Direction preference of optokinetic responses in monocularly tested normal kittens and light deprived cats, Arch. ital. Biol., 116 (1978) 471-477. 11 Van Sluyters, R. C., Reversal of the physiological effects of brief periods of monocular deprivation in the kitten, J. PhysioL (Lond.), 284 (1978) 1-17. 12 Van Sluyters, R. C. and Levitt, F. B., Experimental strabismus in the kitten, J. Neurophysiol., 43 (1980) 686-699. 13 Wiesel, T. N. and Hubel, D. H., Single-cell responses in striate cortex of kittens deprived of vision in one eye, J. NeurophysioL, 26 (1963) 1003-1017. 14 Wood, C. C. Spear, P. D. and Braun, J. J., Direction specific deficit in horizontal optokinetic nystagmus following removal of the visual cortex, Brain Research, 60 (1973) 231-237.
367
Analysis of monocular optokinetic nystagmus in normal and visually deprived kittens
RAFI MALACH, NICK STRONG and RICHARD C. VAN SLUYTERS* School of Optometry, University of California, Berkeley, Cali.[~ 94720 (U.S.A.) (Accepted November 6th, 1980) Key words: optokinetic nystagmus - - kitten - - visual deprivation
The asymmetry of monocular OKN was assessed in normal, monocularly deprived (nondeprived eye) and strabismic cats. No significant differences were observed between the responses of these 3 groups. In young kittens, the gain of OKN for nasalward stimulus movement was larger than that for temporalward. This asymmetry declined to a low residual level by about one year of age. Neurophysiological recordings indicated that the symmetry of OKN is not related to cortical binocularity. Cats reared from birth with one eye sutured dosed suffer marked deficits in their visual capacities, and in the response properties of their visual neurons, when tested through that eye later in life. Recently, it was reported that monocularly deprived (MD) cats also may manifest abnormal visuomotor behavior when tested through the non-deprived eye. Optokinetic nystagmus ( O K N ) elicited by stimuli moving from nasal-to-temporal in the visual field of this eye (T-OKN) was 'irregular' or even 'negative,' while O K N in response to temporal-to-nasal movement (N-OKN) was 'regular'S. Current evidence suggests that, in the cat, T - O K N is dependent upon descending cortico-pretectal pathways, while N - O K N can be mediated by direct retino-pretectal connections2,3,14. Since prolonged periods of M D are known to cause a sharp decrease in cortical binocularity lz, it was suggested that abnormal O K N responses through the non-deprived eye were a result of this loss of binocularity 10. This raised the intriguing possibility that normal development of the descending cortical-pretectal pathways subserving the non-deprived eye was in some way dependent upon the presence of a balanced level of competitive interaction between afferent sensory pathways from the two eyes early in life. However, M D is not the most suitable preparation for studying the role of cortical binocularity in O K N since, in addition to losing binocular cells, M D cats also undergo a massive shift in cortical ocular dominance so that few cells retain functional connections with the deprived eye6,13. There is also the possibility that preventing *To whom correspondence should be addressed.
368 pattern vision neonatally may hinder normal development of the direct retinopretectal pathways involved in O K N ~. To clarify this situation, we have studied monocular O K N in normal cats, MD cats and cats reared with divergent strabismus - - a procedure known to cause a loss of cortical binocularity that is not associated with a shift in ocular dominance 5,1'. All of the techniques and procedures used to rear animals, impose visual deprivation and record from single units in the visual cortex are described in detail elsewhere11,1'. In the present study, M D (eyelid suture) or divergent strabismus (medial rectus tenotomy) was induced within a week of natural eye opening. Monocular O K N was recorded from hand-held animals positioned at the center of a large drum (112 cm diameter × 117 cm high). The drum was rotated at velocities ranging from 4 ° to 50°/sec. The inner surface of the drum was covered with one of two repetitive, high-contrast (86 °/o, background luminance -: 6 cdm -2) patterns. These patterns consisted of either dark vertical stripes whose width was 10', or a random array of dark spots whose diameters ranged from 0.6 ° to 10°. No consistent differences were observed in the O K N elicited by these two patterns, and most of the data reporMONOCULARLY DEPRIVED
NORMAL
1 mY
STRAB I S M I C
2 sec
2O AREA 17 In -.I ..J
N = 3"3
N= 3
N= 32
10
U
,,0
o
1 2 3 4 5 6 7
VU
'v'U
1 2 3 4 5 6 7
r-q VU
1 2 3 4 5 6 7
~ 2o AREA z
N=32
1
234
5
N=30
67
1 2 OCULAR
34
6
N= 31
6
7
1
234
56
7
VU
DOMINANCE
Fig. 1. Monocular O K N and cortical ocular dominance in normal, MD and strabismic cats. Data shown in the left-hand column are from a 6-month-old normal cat (K666), those in the middle column are from a cat monocularly deprived from near birth to 4 years of age (K146) and those in the righthand column are from a cat given a divergent strabismus neonatally and studied at 6 months of age (K619). For all the O K N responses, stimulus velocity was 24°/sec and eye movements to the left are indicated by an upward deflection of the record. Cortical units were classified into one of seven ocular dominance groups according to the criteria of Hubel and Wiesel4. Arrows indicate units dominated by the deprived eye of the MD cat. Top row, N - O K N responses; second row, T-OKN responses; third row, ocular dominance histograms for area 17; and bottom row, ocular dominance histograms for area 18.
369 ted here were obtained with the spot array. Eye movements were recorded using DClinked, bitemporal, EOG skin electrodes (In Vivo Metric). In many cats, single units were recorded from striate and parastriate cortex (areas 17 and 18, respectively) at the conclusion of these O K N measurements. When normally reared cats or cats subjected to prolonged periods of either M D or strabismus were placed in the drum, it immediately became apparent that vigorous and regular T - O K N could be elicited by stimulating either eye of the normal and the strabismic cats, or by stimulating the non-deprived eye of the M D cats. Samples of the O K N records for a normal cat and for two of the cats exposed to prolonged periods of deprivation are shown in Fig. 1, together with the ocular dominance histograms obtained for ceils recorded from areas 17 and 18 in these cats. There is no obvious impairment of T - O K N relative to N - O K N in either the M D cat or the strabismic cat despite the virtual absence of cortical binocular cells in each of these cats. Our initial qualitative impressions were born out by subsequent quantitative analysis of the O K N data. This was accomplished by calculating an 'asymmetry index' (AI) for each cat, which is given by: vt AI ----- 1 - - Vn where Vt is the T - O K N slow-phase velocity and Vn is the N - O K N slow-phase velocity. An AI of 0.0 indicates equal O K N gain in both directions (no asymmetry) and an AI of 1.0 indicates total loss of T - O K N (maximum asymmetry). The AI values for the 3
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AGE
Fig. 2. Asymmetryof monocular OKN during development. An index of the asymmetryin monocular OKN responses was calculated for each recording session in 44cats of various ages (see text for details). To .qualifyfor this form of analysis, an eye movementrecord for a givenstimulus velocityhad to contain a minimum of 10 consecutiveOKN beats for cats over 4 months of age, and 5 consecutivebeats for cats younger than 4 months. All the data presented in this figure were collected using a stimulus velocityof 24°/see. The asymmetry index is plotted as a function of the ago at recording (log scale) for normal (unfilled circles, n = 23), MD (non-deprived eyes only, filled circles, n = 17) and strabismic (crosses, n = 4) cats. Points connected by lines represent data collected from the same eye at different ages (see text). Upward and downward pointing arrows indicate pairs of points representing data collectedfrom both eyes of the same cat (either normal or strabismic) during a single recording session.
370 cats in Fig. 1 were 0.37, 0.24 and 0.18 for the normal, M D and strabismic cats, respectively. Although we failed to find any significant increase in the asymmetry of monocular O K N responses from animals subjected to prolonged periods of deprivation, it was still conceivable that deprivation differentially affected the rate of development of T and N - O K N in kittens. To examine this possibility, we studied the development of monocular O K N in normal and visually deprived kittens. Early in this project we found, as has been described by others 1,7, that the vigor of O K N rapidly declines with repeated testing. Therefore, it was decided to conduct a cross-sectional study of monocular O K N in a large sample of kittens of various ages, as a first step toward studying the development of O K N . Recording was limited in each kitten to just a few sessions separated by at least 3 weeks. The results of this cross-sectional study of 44 cats are given in Fig. 2, where the asymmetry index is plotted as a function of the age at recording for normal, M D and strabismic kittens. Inspection of this figure reveals that the O K N responses obtained from young M D or strabismic kittens can exhibit marked asymmetry, both in terms of the gain and the regularity of the response. However, this asymmetry is not a consistent finding in visually deprived kittens of a given age, and, more importantly, normal kittens of the same age often produced equally asymmetric responses. These data from developing kittens are obviously quite variable, but there is an unmistakable trend toward reduced asymmetry with increasing age regardless of the rearing paradigm employed. While all the data presented in Fig. 2 were obtained using a stimulus velocity of 24°/sec, there were also no consistent differences between these 3 groups of animals when stimulus velocities ranging from 4 ° to 50°/sec were employed. The data presented here fail to confirm those of van Hof-van Duin 8, who found deficient T - O K N in the non-deprived eye of cats subjected to prolonged M D from birth. We find no evidence of a consistent difference at any age, when the monocular O K N responses of M D kittens are compared to those of normal kittens. We do find marked asymmetries in some deprived kittens (see Fig. 2), but normal kittens of the same age can exhibit equally large asymmetries. A possible source of some of the discrepancy between these two studies might be differences in the methods used to assess eye movements. First, van H o f - v a n Duin chose to use direct observation of the eyes to evaluate O K N responses in hand-held animals rather than the DC-linked EOG signals that were employed in the present study. A second possibility stems from differences in the frequency with which animals were subjected to O K N recording. Whereas van H o f - v a n Duin studied O K N extensively in each cat 8, recording from the same cat as often as once a day 9, we limited recording to very few sessions (often only one with each cat), separated by long intervals, and sampled across a large number of cats. It may be that normal and visually deprived cats differ in terms of the rate of habituation of their T - O K N responses - - a question we are currently investigating. We found no evidence of T - O K N specific deficits in several cats reared with prolonged periods of either M D or strabismus - - two conditions known to produce a marked reduction in cortical binocularity. However, even if M D did cause changes in
371 T - O K N responses for the non-deprived eye of some cats, these deficits could not be due solely to changes in cortical binocularity since prolonged M D always causes a dramatic decrease in the proportion of cortical binocular neurons. An example of this lack of correlation is demonstrated by our results from cats exposed to prolonged periods of MD or divergent strabismus. In these animals, cortical binocularity was reduced severely (see Fig. 1), but T - O K N was not selectively depressed. It is possible that there is some other, less reliable, neurophysiological consequence of MD that can cause altered T - O K N through the non-deprived eye. For example, Hoffmann 2 has reported that MD can cause a loss of ipsilateral input to the nucleus of the optic tract (a pretectal center thought to mediate horizontal OKN) bilaterally. However, since monocular O K N responses were not assessed in these cats and no data were presented regarding the reliability of this neural loss, it is difficult to evaluate the functional significance of this finding. Our analysis of the development of monocular O K N in normal kittens (see Fig. 2) confirms and extends van Hof-van Duin's 10 observation that N - O K N appears earlier than T-OKN. It is important to realize how slowly T-OKN matures. In most kittens, monocular O K N responses are quite asymmetric until around 10 weeks of age. This is interesting in view of the suggestion that N - O K N can be mediated by direct retino-pretectal pathways but that T-OKN is dependent upon an indirect corticopretectal input ~4. It would be misleading to leave the impression that prolonged MD fails to alter monocular O K N in the cat. In this paper we have presented only those data related to performance through the non-deprived eye. We have found marked changes in O K N performance in a preliminary experiment where stimuli were presented to the deprived eye alone. We are currently studying the role of functional deficits in the retinothalamo-cortical pathways in producing these changes. We are grateful for assistance from M. Stone and G. Fuller in recording eye movements, F. Levitt in recording single units, R. Huppenbauer in reconstructing electrode tracks and C. Nicholson in typing and editing the manuscript. This research was supported partially by a research fellowship from the Alfred P. Sloan Foundation, a research grant from the National Institutes of Health (EY 02193) and a National Institutes of Health Biomedical Sciences Research Grant (RR 07006) awarded to R.C.V.S.
1 Braun, J. J. and Gault, F. P., Monocular and binocular control of horizontal optokinetic nystagmus in cats and rabbits, J. comp. physiol. Psychol., 69 (1969) 12-16. 2 Hoffmann, K.-P., Optokinetic nystagmus and single-cellresponses in the nucleus tractus opticus after early monocular deprivation in the cat. In R. D. Freeman (Ed.), Developmental Neurobiology of Vision, Plenum Press, New York, N.Y., 1979, pp. 63-72. 3 Hoffmann, K.-P. and Schoppmann, A., Retinal input to direction selective cells in the nucleus opticus tractus of the cat, Brain Research, 99 (1975) 359-366. 4 Hubel, D. H. and Wiesel, T. N., Receptive fields, binocular interaction and functional architecture in the cat's visual cortex, J. Physiol. (Lond.), 165 (1962) 559-568.
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