Alteration of electrical correlates of sensory processing by tetrahydrocannabinol.

The action of tetrahydrocannabinol on the function of four multimodality responsive neocortical areas was assessed in the cat. Cats, anesthetized with alpha-chloralose, were subjected to auditory, somatosensory, and two types of visual stimulation. Simultaneous evoked field potentials and multiple-unit activity were recorded. The drug produced a significant reduction in evoked field responses at the three most rostral cortical areas, whereas responses at the posterior suprasylvian gyrus were spared. There were no significant differences between sensory modalities. In addition to being the first pharmacological study to demonstrate differential drug sensitivity between these polysensory areas, these studies localized an effect of tetrahydrocannabinol. Sensory evoked multiple-unit activity showed a pattern of change after THC consistent with a reduction in activity of pyramidal output cells and a concomitant increase in interneuron activity. The action of tetrahydrocannabinol on polysensory systems is important in attention and orientation.