Effects of delta9-tetrahydrocannabinol and pentobarbital on a cortical response evoked during conditioning.

A surface-negative wave, evoked by tone cues, appeared in monkey post-arcuate cortex as the monkey learned that the cue signaled the availability of reward. This evoked activity was depressed, concomitantly with changes in the animal's behavioral responding, by doses of delta9-tetrahydrocannabinol (delta9-THC) as low as 0.032 mg/kg and of pentobarbital as low as 4 mg/kg. Pentobarbital tended to increase the latency of the evoked wave, an effect not seen with delta9-THC.