Prefrontal cortex neuron activity during a discriminative conditioning paradigm in unanesthetized rats.

Single neuron responses were recorded from the prefrontal cortex of unanesthetized, restrained rats trained to a discriminative conditioning paradigm. The animals were preconditioned to a tone paired with footshock (CS+) and a second tone presented unpaired (CS-). Only neurons with large amplitude, positive first deflection action potentials were studied. Eighty-five percent of the units (17 of 20) emitted conditioned responses in that the response to either one or both of the conditioned stimuli (CS) was significantly different from spontaneous activity. Thirty-five percent of the units emitted differential conditioned responses in that the responses to one of the CS was significantly different than the response to the other CS and that the response was subsequently shown to extinguish when the footshock was withheld. The neurons which emitted the differential conditioned responses appeared to be located in the deeper layers of the anteromedial prefrontal cortex while the remaining neurons were located either in more superficial layers or anterior aspects of the prefrontal cortex. The results suggest that the anteromedial prefrontal cortex may be involved in neural mechanisms related to discriminative conditioning.