Optical imaging of neural activity of core and belt fields of guinea-pig auditory cortex in response to duration of sounds

How the duration of sounds is processed in the core and belt fields of the guinea-pig auditory cortex was studied by optical imaging with a voltage-sensitive dye (RH795). The animals were anesthetized with ketamine (80 mg/kg) and xylazine (40 mg/kg). Tone and noise bursts with 5-ms onset and offset ramps were presented at different durations (10, 15, 30, 60, 100, and 200 ms) and at 50-70 dBSPL by a loudspeaker located contralateral to the recording cortex. Neural activity was recorded from the core (AI and AII) and ventroanterior belt (VA) fields. Responses of AI, AII and VA to tone or noise bursts consist of a phasic-on excitatory and a following inhibitory response. In AI and AII, the amplitude and duration of the response did not change when the duration of the tone and noise bursts was changed. The duration of the response to the noise burst was shorter than that to the tone burst. In VA, the amplitude and duration of the response increased significantly when the duration of the noise burst was increased. The increase of amplitude and duration was observed for the noise with more than 100 ms and more than 30 ms durations, respectively. The response in VA to the tone burst, however, showed no change in amplitude and duration when the duration of the tone burst was changed. We discuss the differences in integration of temporal and spectral information between the core and the VA field. [Jpn J Physiol 54 Suppl:S168 (2004)]