OPTICAL STUDY OF SPATIOTEMPORAL INHIBITION EVOKED BY 2-TONE SEQUENCESIN THE GUINEA-PIG AUDITORY-CORTEX

Spatiotemporal response patterns in the anterior and dorsocaudal field s of the guinea pig auditory cortex after two-tone sequences were stud ied in anesthetized animals (Nembutal 30 mg kg(-1)) using an optical r ecording method (voltage-sensitive dye RH795, 12 x 12 photodiode array ). Each first (masker) and second (probe) tone was 30 ms long with a 1 0-ms rise-fall time. Masker-probe pair combinations of the same or dif ferent frequencies with probe delays of 30-150 ms were presented to th e ear contralateral to the recording side. With same-frequency pairs, responses to the probe were inhibited completely after probe delays of less than 50 ms and the inhibition lasted for more than 150 ms, and t he inhibition magnitudes in different isofrequency bands of the anteri or field were essentially the same. With different-frequency (octave-s eparated) pairs, responses to the probe were not inhibited completely even after probe delays as short as 30 ms, and the inhibition lasted o nly for 110-130 ms. Inhibition magnitudes were different from location to location.