Neuromagnetic responses to frequency-tagged sounds: a new method to follow inputs from each ear to the human auditory cortex during binaural hearing.

Binaural cortical responses are mixtures of inputs from both ears. We introduce here a novel method that allows, for the first time, to selectively follow these inputs in humans up to the cortex during binaural hearing. We recorded neuromagnetic cortical responses to amplitude-modulated continuous tones, with different modulation frequencies at each ear. During binaural hearing, the left- and right-ear inputs competed strongly in both auditory cortices: the right-hemisphere responses were symmetrically suppressed, compared with monaural stimulation, for sounds of both ears, whereas the left-hemisphere responses were suppressed significantly more for ipsilateral than contralateral sounds, thereby intensifying the right-ear dominance of the left auditory cortex. This type of hemisphere- and ear-selective information on cortical binaural interaction could have important applications in human auditory neuroscience.