OPTICAL-RECORDING OF AZIMUTH REPRESENTATION IN GUINEA-PIG AUDITORY-CORTEX

The frequency dependency of directional sensitivity of the auditory co rtex of barbiturate-anesthetized guinea pigs in response to tone burst s was studied bq an optical equipment and a voltage sensitive dye (RH7 95). Tone bursts at 4, 8 and 14 kHz were presented from loudspeakers p laced at the azimuths from contralateral 90 degrees to ipsilateral 90 degrees in 30 degrees steps on a front-horizontal semi-circular board (100 cm in radius). The maximum responses were observed at around cont ralateral 30 degrees (best azimuth). The onset and peak latencies were the shortest at the best azimuth. The best azimuth was the same for a ll these frequencies, but the azimuth selectivity became broader for t he lower frequencies. These results indicate that the azimuth selectiv ity observed in the guinea pig auditory cortex is mainly associated wi th pinna characteristics.