Cholinergic modulation of sensory responses in rat primary somatic sensory cortex.

Responses evoked in single neurons of the primary somatic sensory cortex following tactile stimulation were examined before, during and after local iontophoretic application of acetylcholine (ACh) in urethane-anesthetized rats. The most common effect of ACh was an enhancement of the discharge evoked by sensory stimuli. Some cells responded to sensory input only in the presence of ACh. Response enhancement was observed in both supra- and infragranular layers, whereas response suppression was the most common effect in layer IV. These studies suggest that cholinergic systems modify sensory processing in cerebral neocortex by modulating the effectiveness of afferent inputs to cortical neurons in all layers.