The tonotopic representation in the auditory cortex of the guinea pig with optical recording.

We examined spatio-temporal characteristics of the tonotopic representation in the auditory cortex of the anesthetized guinea pig with a multichannel optical method using voltage-sensitive dye. The response latencies increased, and the response field in the cortex became small when the stimulus intensity levels were decreased. Low frequencies were represented rostrally and high frequencies caudally. The two fields responding to different frequencies at higher intensity levels gradually overlapped as time after stimulus onset increased, though these response field did not overlap at the beginning of the response. These findings indicate that tonotopic representation varies dynamically with time after stimulus onset.