Effects of rearing kittens with convergent strabismus on development of receptive-field properties in striate cortex neurons.

Convergent strabismus was induced surgically in seven kittens at 3 wk of age. Recordings were made in 131 cells in the striate cortex of these strabismic kittens after maturation, and the results were compared to the data obtained from 140 striate neurons in normally reared cats. All our samples had receptive fields (RFs) within 5 degrees of the area centralis. The spatial and temporal response properties were quantitatively analyzed by using drifting sinusoidal gratings of various contrasts as well as spatial and temporal frequencies. In contrast to other reports, the receptive-field properties of the striate neurons exclusively driven or dominated by the deviating eye were quite abnormal. The spatial frequency tuning curves in strabismic cats were different from those obtained from normals in that the optimal spatial frequencies and spatial resolutions were shifted to lower values and the bandwidths were significantly broader. The contrast-response functions show that contrast thresholds, measured at the optimal spatial frequency, were significantly higher and the slope of the functions much flatter in strabismic animals. Moreover, receptive-field sizes were much larger and the sharpness of orientation tuning was reduced in strabismic cats. Direction selectivity, however, was normal in those animals. The temporal frequency tuning curves were also abnormal, particularly in that temporal resolution was considerably reduced in strabismic cats compared with normally reared cats. In addition, many cells in strabismic animals exhibited much longer latencies to visual and optic chiasm (OX) stimulations. All these effects, to our great surprise, were also observed in the striate units controlled by the nondeviating eye, although the magnitude of the alteration depends on the receptive-field property. The abnormalities found in spatial frequency tuning, contrast thresholds, and RF sizes were as severe as those revealed in the deviating eye. On the other hand, the effects on other RF properties were minimal or less severe. These physiological findings correspond very well with results from behavioral measurements of spatial contrast sensitivity in the same cats reported elsewhere. It is concluded from these results that the nondeviating eye in convergent strabismic animals, and perhaps humans, should not always be presumed "normal."