Time course of tonal frequency-response-area of primary auditory cortex neurons in alert cats

Cells in the A1 auditory cortex of alert animals show various response time-courses during pure-tone stimuli: tonic, phasic-tonic, and phasic. Previously the time course of the spike firing rates was examined at a characteristic frequency (CF) or in a range of frequencies including CF. We investigated time-course of the frequency-response-area (FRA) during pure-tone stimuli in A1 cells of alert cats. The short rise/fall time (0.1-2 ms) and long stimulus duration (0.5 s) was used for investigation of the time course. FRA changed with time drastically in the phasic cells, mildly in the phasic-tonic cells, but not in the tonic cells. The best-response frequency (BF) within FRA was constant throughout the stimulus duration in the tonic and phasic-tonic cells, but was difficult to define in the phasic cells. The phasic firing properties of the phasic cells were preserved even during the bandnoise stimuli at various bandwidth and spectral locations. The variability of FRA time-course between cell types may play a role for analyzing auditory spectral cues that vary with a wide range of time constant.