REAL-TIME IMAGING OF NEURAL ACTIVITY DURING BINAURAL INTERACTION IN THE GUINEA-PIG AUDITORY-CORTEX

Spatio-temporal patterns of binaural interaction in the guinea pig aud itory cortex (AC) were observed using optical recording with a 12 x 12 photodiode array and a voltage-sensitive dye. The amplitudes of the s ound-induced light signals from the cortex were transformed into seque ntial two-dimensional images every 0.58 ms. Binaural sound stimuli evo ked an excitatory response followed by a strong inhibition, and contra lateral stimuli evoked a strong excitatory response followed by a weak inhibition. Ipsilateral sound stimuli evoked a weak response. Binaura l stimulation induced two types of ipsilateral inhibition: a fast bina ural inhibition which was detected only after the contralateral and ip silateral responses were subtracted from the binaural responses, and w hich appeared 12-25 ms after the onset of stimulation, and a slow bina ural inhibitory effect which was clearly observed in the binaural resp onses themselves, appearing 70-95 ms after the onset of stimulation. T he fast binaural inhibition was observed in the same area as the contr alateral excitatory response. The inhibited area became stronger and m ore widespread with increasing intensity of ipsilateral stimulation. W e did not observe the specialized organization of binaural neurons as electrophysiologically found in the cat AC, in which binaural neurons of the same binaural response type are clustered together and alternat e with clusters of other response types.