Corticofugal influences on the background activity of the rabbit lateral geniculate body]

Two groups of P-neurons were found in the rabbit lateral geniculate body: with lowfrequency and high-frequency background activity. The background activity of the low-frequency neurons was subjected mainly to facilitatory coritcofugal influences. Inhibitory corticofugal influences predominated in the regulation of background activity of high-frequency neurons.     

Orientational tuning of visual cortex neurons to different stimulus intensities in the cat

The orientation tuning of field 17 neurons of the visual cortex was studied in immobilized and unanesthetized cats under different intensities of test light slits and constant light background. Orientation tuning of five neurons was invariant to stimulus intensity: their preferential orientation did not change. Thirteen cells were variable as during the change of the contrast they showed a statistically significant displacement of orientation tuning from 22 degrees to 90 degrees. Changes in other neurons were not significant. Invariant neurons differed from variable ones in several characteristics. The mechanisms of orientation tuning changes during contrast variations are discussed.