Prefrontal cortical cell firing during maintenance, extinction, and reinstatement of goal-directed behavior for natural reward.

The prefrontal cortex (PFC) is important for higher cognitive functioning and the processing of reward-related information. Here, electrophysiological recording procedures were used to examine cell firing in the PFC in rats (n = 12) during water reinforcement sessions consisting of three phases. In phase one (maintenance), animals pressed a lever (fixed ratio 1) for water reinforcement (0.05 ml/press) paired with an auditory stimulus. Of 62 neurons recorded during maintenance, 39 (63%) exhibited one of three types of patterned discharges relative to the reinforced response for water. Specifically, PFC neurons exhibited increases in firing rate within seconds preceding the response (type PR; n = 9 cells) or increases (type RFe; n = 16 cells) or decreases (type RFi; n = 14 cells) in firing rate immediately following response completion. The remaining neurons did not alter their firing profiles relative to the reinforced response (type nonphasic cells; n = 23 cells). In phase two (extinction), lever press responses had no programmed consequences (i.e., water reinforcement and the auditory stimulus were not presented). After 30 min of no responding, phase three (reinstatement) began, during which each lever press response was again associated with water reinforcement paired with the stimulus. Results indicate differential effects of extinction/reinstatement on cell firing rates and patterns dependent on cell type. These findings are discussed with respect to the adaptive nature of PFC activity during goal-directed behaviors for "natural" rewards, and are considered relative to prior studies that examined nucleus accumbens cell firing during a similar behavioral task. 2005 Wiley-Liss, Inc.