AUDITORY CORTICAL FUNCTIONS STUDIED BY IN-VIVO OPTICAL RECORDING METHOD

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Using an optical recording method with a 12 * 12-channel photodiode array and a voltage-sensitive dye (RH795), spatiotemporal patterns of neural activities in anterior (A : primary) and dorsocaudal (DC) fields of the guinea pig auditory cortex were measured under anesthetized condition (Nembutal 30 mg/kg). In this research, two projects were conducted : (1) binaural interaction and (2) information processing of frequency-modulated (FM) sounds and animal calls.To measure binaural interaction, we used both free-field stimulation and closed-ear stimulation. The optically-recorded responses to free-field stimulation showed that the responses were maximal when the speaker was placed at around 30 degrees contralateral to the recoding side and small when it was placed on the ipsilateral side. The azimuth selectivity was sharper for higher frequencies and broader for lower frequencies. These response patterns were suggested to be a reflection of pinna characteristics. Cortical locations specif … More ically responding to a certain azimuth were not observed, indicating that there is no topographic representation of azimuth in fields A and DC.Closed-ear stimulation revealed that the excitation was evoked mainly contralaterally and the inhibition was evoked mainly ipsilaterally. This excitation and inhibition occurred at the same cortical places in both fields.The responses to FM sounds and animal calls were different from those to pure-tones. The response to a pure-tone moved dorsally along an isofrequency band, but those to FM sounds moved obliquenly crossing different isofrequency bands. The direction of the response movement was opposite between upward and downward frequency sweeps. The responses to animal calls were very complicated : they showed several times repetition of excitation and inhibition during the calls. No cortical place which specifically responds to FM sounds and the calls was found. These results indicate that spatiotemporal patterns in response to the FM sounds and the calls are related to the temporal structures of spectral components of these sounds. Less