Phasic and long-term excitability changes in prepyriform cortex of cats.

Abstract The olfactory cortex of cats was repeatedly stimulated through electrodes implanted 14 to 18 months. Frequency-response and time-response curves based on potentials evoked in this cortex were obtained from cats naive to the electric stimulus, oriented and then habituated, and trained to press a bar for milk upon receipt of the stimulus. Wide differences among cats were resolved by using a system of analysis that treated the evoked potential as a damped sinusoidal oscillation, having the four parameters of amplitude, frequency-spectrum, phase of onset, and Q . Daily stimulation after orienting the cats to the stimulus had the cumulative effect of lowering the frequency of the evoked potential and inceasing the number of component frequencies, leading to irregularities in curves and to individual differences. The process required several months to reach a stable endpoint, and was more extensive in attentive than habituated cats. It was fully reversible in the latter. This shift rendered long-term comparisons of amplitude and Q unreliable. A phasic change was identified, consisting of a combined increase in peak-frequency, decrease in amplitude, and decrease in Q , which took place in normally attentive cats during postextinction habituation to the stimulus, and in dehabituated cats undergoing repeat postorientation habituation. It was fully reversed in normally attentive cats by retraining and in habituated cats by several days' remission of stimulation.