Effect of Nembutal on neuronal responses in the visual cortex

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1. After administration of Nembutal (25–30 mg/kg) changes take place in the evoked potential and unit response of cortical neurons: amplitude of the primary surface-positive wave is increased, the slow surface-negative wave is shortened, and after 80–120 msec a new surface positive-negative wave appears, followed by another series of similar waves. In the unit response of certain neurons (types B1, B2 and M) the inhibitory pause is shortened by the appearance 80–120 msec after the flash of a new group of discharges, as a rule correlating well with the newly appearing surfacepositive and deep-negative wave. No distinct changes are seen in neurons with type D responses. 2. For the most common response in rabbits anesthetized with Nembutal the first activation phase has a shorter latent period and is of short duration. 3. The recovery cycle of cortical neuronal responses after administration of Nembutal is shortened. It is postulated that the inhibitory processes evidently responsible for the phase of subnormality in the recovery cycle of the responses after the first stimulus, are weakened.