Journal of Neuroscience, Vol 12, 4521-4529, Copyright © 1992 by Society for Neuroscience
Spatiotemporal sensitivity following lesions of area 18 in the cat
T Pasternak and JH Maunsell
Department of Neurobiology, University of Rochester, New York 14627.
The contribution of cat area 18 to spatiotemporal sensitivity and to motion
processing was assessed in cats with unilateral ibotenic acid lesions
placed in physiologically identified portions of area 18. The lesions were
centered in the representation of the lower right visual field, about 10
degrees from the vertical meridian. In one of the animals, the lesion
invaded a small portion of area 19. We measured detectability of various
spatiotemporal stimuli placed within the lesioned and intact portions of
the visual field, while monitoring eye position with a scleral search coil.
We found a loss of sensitivity to gratings of low and intermediate spatial
frequency, within the ablated portion of the visual field. The sensitivity
loss was 0.6-1.0 log units at low and intermediate spatial frequencies, and
decreased at higher frequencies with the resolution limits remaining
intact. The loss extended over a range of temporal frequencies for both
drifting gratings and grating modulated in counterphase. We also found that
within the lesioned hemifield, the cats were unable to discriminate between
rightward and leftward motion even at the highest contrasts. These results
demonstrate that area 18 plays an important role in detecting drifting low-
and intermediate-spatial-frequency targets and is likely to represent a
critical stage in the cortical processing of motion signals.