HUMAN CORTICAL RESPONSES EVOKED BY DICHOTICALLY PRESENTED TONES OF DIFFERENT FREQUENCIES

BEHAVIORAL and patient studies have suggested that during dichotic lis tening the ipsilateral auditory pathways are strongly inhibited, so th at each hemisphere is treats the sound coming to the contralateral ear . We analysed the auditory N100m neuromagnetic evoked response followi ng passive listening of dichotic tones of different frequencies. We fo und that the N100m in each hemisphere depended on both ipsilateral and contralateral stimuli, revealing no strong inhibition of ipsilateral pathways. The N100m increased with the interaural frequency disparity and was reduced as both ears received identical stimuli. The results c an be explained by the existence of a frequency-dependent excitatory/i nhibitory organization of the auditory cortex, as has been described i n the cat. We suggest that the N100m might also reflect automatic proc esses involved in multiple-stream perception. (C) 1998 Rapid Science L td.