Region-dependent Millisecond Time-scale Sensitivity in Spectrotemporal Integrations in Guinea Pig Primary Auditory Cortex.

ABSTRACT

Spectrotemporal integration is a key function of our auditory system for discriminating spectrotemporally complex sounds, such as words. Response latency in the auditory cortex is known to change with the millisecond time-scale depending on acoustic parameters, such as sound frequency and intensity. The functional significance of the millisecond-range latency difference in the integration remains unclear. Actually, whether the auditory cortex has a sensitivity to the millisecond-range difference has not been systematically examined. Herein, we examined the sensitivity in the primary auditory cortex (A1) using voltage-sensitive dye imaging techniques in guinea pigs. Bandpass noise bursts in two different bands (band-noises), centered at 1 and 16 kHz, respectively, were used for the examination. Onset times of individual band-noises (spectral onset-times) were varied to virtually cancel or magnify the latency difference observed with the band-noises. Conventionally defined nonlinear effects in integration were analyzed at A1 with varying sound intensities (or response latencies) and/or spectral onset-times of the two band-noises. The nonlinear effect measured in the high-frequency region of the A1 linearly changed depending on the millisecond difference of the response onset-times, which were estimated from the spatially-local response latencies and spectral onset-times. In contrast, the low-frequency region of the A1 had no significant sensitivity to the millisecond difference. The millisecond-range latency difference may have functional significance in the spectrotemporal integration with the millisecond time-scale sensitivity at the high-frequency region of A1 but not at the low-frequency region.