Journal of Neurophysiology, Vol 52, Issue 3 538-552, Copyright © 1984 by APS
Effects of strabismus on responsivity, spatial resolution, and contrast sensitivity of cat lateral geniculate neurons
K. R. Jones, R. E. Kalil and P. D. Spear
Rearing cats with esotropia is known to cause a number of deficits in
visual behavior tested through the deviated eye. These include a loss of
orienting response to stimuli presented in the nasal visual field of the
deviated eye, a reduction in visual acuity, and a general reduction in
contrast sensitivity at all spatial frequencies. To assess the involvement
of the lateral geniculate nucleus (LGN) in these deficits, we measured the
following: 1) the visual responsiveness of lamina A1 cells with peripheral
(more than 10 degrees from area centralis) receptive fields in three
esotropic and three normal cats and 2) the spatial resolution and contrast
sensitivity of lamina A X-cells with central (within 5 degrees of the area
centralis) receptive fields in six esotropic and six normal cats. For
comparison, we also measured LGN X-cell spatial resolutions in four
exotropic cats and in two cats raised with an esotropia in one eye and the
lids of the other eye sutured shut (MD-estropes). Recordings from the
lateral portion of lamina A1 in esotropic cats yielded similar numbers of
visually responsive cells with far nasal receptive fields as were seen in
normal animals. Peak and mean response rates to a flashing spot also were
normal. In addition, no differences were found between esotropes and
normals in the percentages of X- and Y-cells encountered. These results
suggest that the loss of orienting response to stimuli presented in the
nasal field (12, 20) is not due to a loss of neural responses in the LGN of
esotropic cats. In addition, they suggest that decreases in cell size in
lamina A1 of esotropic cats (13, 36; R. E. Kalil, unpublished observations)
are not accompanied by marked functional abnormalities of the cells and
that cortical abnormalities ipsilateral to the deviated eye (22) are likely
to have their origin within striate cortex itself. Recordings from lamina A
cells with receptive fields near area centralis revealed that the average
X-cell spatial resolution in esotropes (2.1 cycles/deg) was significantly
lower than that in normal cats (3.1 cycles/deg). This reduction was seen in
all esotropic cats tested and was due both to an increase in the proportion
of X-cells with very low spatial resolution and to a loss of X-cells
responding to high spatial frequencies (greater than 3.25 cycles/deg). The
average spatial resolution of X-cells driven by the deviated eye in
MD-esotropes fell midway between those of esotropes and normals. In
exotropes, mean X-cell spatial resolution was normal.(ABSTRACT TRUNCATED AT
400 WORDS)
