Journal of Neuroscience, Vol 12, 4721-4736, Copyright © 1992 by Society for Neuroscience
Development of binocular vision in the kitten's striate cortex
RD Freeman and I Ohzawa
Group in Neurobiology, School of Optometry, University of California, Berkeley 94720.
Studies of the development and plasticity of the visual pathway are well
documented, but a basic question remains open: what is the physiological
status of the system prior to extensive visual experience? Somewhat
conflicting answers have been put forward, and in a major area, binocular
vision, reports have ranged from severe immaturity to well-developed
maturity. This is an important question to resolve since binocular cells in
the visual cortex are thought to be the neural substrate for stereoscopic
depth perception. We have addressed this question by recording from single
cells in the striate cortex of kittens at postnatal ages 2, 3, and 4 weeks
and from adults for comparison. Gratings with sinusoidal luminance
distribution are presented to left, right, or both eyes. For each cell, we
determine optimal values for orientation and spatial frequency. Relative
phase (retinal disparity) is then varied in a dichoptic sequence so that
binocular interaction may be studied. Results are as follows. In the normal
adult, we have shown in previous work that most binocular interaction in
the visual cortex can be accounted for on the basis of linear summation.
Results from 3 and 4 week postnatal kittens are closely similar to those
from adults. All types of binocular interaction found in adults are present
in kittens. This includes phase- specific and non-phase-specific
suppression or facilitation. Furthermore, monocular and binocular tuning
characteristics are comparable in kittens and adults. The clear changes
that occur with age are optimal spatial frequencies and peak responses. In
addition, at 2 weeks, there is a substantially higher proportion of
monocular cells compared to other ages and correspondingly, lower relative
numbers of cells that exhibit phase-specific or suppressive binocular
interactions. From increases in optimal spatial frequency and
interpupillary distance with age, we calculated predicted changes in
binocular disparity thresholds (stereo acuity) with age. Although there are
methodological limits with respect to the behavioral testing of young
kittens, the predicted results are comparable to some of the values
obtained. Considered together, our results show that the physiological
apparatus for binocular vision is functional at an early stage in postnatal
development. It is possible that the connections that underlie this
function are developed rapidly during early postnatal experience. An
alternative possibility is that there is an elaborate genetic organization
of binocular vision, but our study does not address this issue directly. A
combination of these factors may be applicable.(ABSTRACT TRUNCATED AT 400
WORDS)
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