| Abstract: | Directional tuning was investigated in 40 neurons of the primary visual cortex (area 17) before and after Nembutal injection during acute experiments on immobilized cats. Preferred orientation (PO) in 50% of neurons was found to be stable after the drug, while the remainder showed a consistent shift in PO (averaging 53.6±8.0°) for a number of hours. Neurons with consistent PO more frequently showed a preference for horizontal and vertical stimulus orientation; cells with unstable tuning had a wider PO distribution. More refined directional detection (i.e., finer tuning) was noted in "stable" rather than in "unstable" neurons both before and after administering the drug. Under narcosis, directional tuning altered in 50% of cells — an effect more marked in "unstable" than in "stable" cells (68% as against 38%). Mean background discharge rate also fell by an average of 5.5-fold and induced firing rate declined 1.5-fold during narcosis, moreover.Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 669–676, November–December, 1991. |
