Optically measured spatio-temporal distribution of excitation and inhibition evoked by two-tone sequences within the guinea pig auditory cortex

Abstract

Spatio-temporal distributions of excitation and inhibition in the anterior (A) and dorsocaudal (DC) fields of the guinea pig auditory cortex after two-tone stimuli were studied in anesthetized animals (Nembutal 30 mg/kg) using an optical recording method (voltage-sensitive dye RH795, 12×12 photodiode array). Each first (masker) and second (probe) tone was 30 ms long and the probe delay was varied from 30 to 150 ms. Frequencies of the masker and the probe were either the same or octave-separated. With same-frequency pairs, responses to the probe were suppressed completely after probe delays of less than 50 ms and the inhibition lasted for 130 ms. With different-frequency pairs, they were not suppressed completely even after probe delays as short as 30 ms, and the inhibition lasted for only 90–110 ms. The magnitude of the inhibition induced by the same-frequency masker was very similar among locations within the cortical fields, but that by the different-frequency masker differed according to the location. These results are discussed in terms of spectro-temporal masking effects. [Work supported by HFSP and the Ministry of Education in Japan.]