Figure 5.

A subpopulation of neurons developed a phasic inhibition to the empty port during acquisition of extinction. Early extinction began at the onset of the extinction epoch, when sucrose was unavailable. Late extinction is defined as beginning on the first trial when the latency between the nosepoke response and the subsequent port entry is 2 SDs greater than the session mean. A, Temporal dynamics of three neurons that developed a phasic inhibition to the empty port from a representative rat. Surface plot of normalized firing rate was calculated using 150 ms bins, and was smoothed for ±1 trial. B, Microanalysis of behavior during the extinction epoch. Given that a nosepoke response occurred, the probability of occurrence of the next behavioral response did not change from early to late extinction. Given that a port entry occurred, the probability that the rat would perform another port entry before performing a nosepoke increased during late extinction (p < 0.05). C, The proportion of neurons that developed a phasic inhibition upon empty port entry only during extinction was inversely correlated with response intensity.