Journal of Neuroscience, Vol 8, 2491-2506, Copyright © 1988 by Society for Neuroscience
Monocularly deprived cats: binocular tests of cortical cells reveal functional connections from the deprived eye
RD Freeman and I Ohzawa
Group in Neurobiology, University of California, Berkeley 94720.
Animals that are deprived of vision in one eye during a vulnerable phase of
development lose visual function of the eye. Although this phenomenon has
been studied extensively, little is known about the mechanism of
disconnection of the deprived eye from visual cortex. One fundamental
question is whether input remains from that eye. We have examined the
hypothesis that there is functional input from a deprived eye to visual
cortex that cannot be observed with standard alternate tests of each eye.
We have employed a robust visual stimulation procedure in which large
sinusoidal gratings are presented to each eye, as well as to both eyes
together, at varying relative phases or retinal disparities. Monocular and
binocular stimulation was used to test kittens unilaterally deprived for
brief, intermediate, or long periods. A fourth group of kittens was studied
as normal controls. Standard methods were used to record from single cells
in the striate cortex. After initial qualitative exploration of receptive
fields, all testing and analysis were quantitative. As expected, monocular
tests revealed that, for most cells, the deprived eye was ineffective,
i.e., did not activate the unit. This effect was increasingly pronounced as
the length of deprivation was increased. However, binocular tests revealed
that a large fraction of these cells (30-40%) was clearly influenced by and
therefore functionally connected to the deprived eye. This interaction was
phase-selective, or suppressive and not selective for phase. There was no
indication that the connections that remained were of a specific type,
i.e., excitatory or inhibitory. Therefore, excitation and inhibition appear
equally resistant to the effects of monocular deprivation. However, with
long-term deprivation, we find minimal evidence of functional input from
the deprived eye. We conclude that the effects of monocular deprivation
occur over a considerably longer time period than was previously thought.
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