Distributed current analyses of bi-hemispheric magnetic N1m responses to ipsi/contralateral monaural stimuli from a single subject.

Magnetoencephalographic (MEG) responses of both auditory cortices to simple auditory stimuli presented monaurally to either ear were recorded from a single subject. A distributed current model and a current dipole model were used to analyse the responses at the latency of the dominant N1m complex. At the N1m the current density was localised to a single area and was consequently well modelled by a single current dipole close to the peak current density. In the left hemisphere, the contralateral response (as identified by the peak current density) preceded the ipsilateral response by 3 msec. This value was 7 msec for the right hemisphere. Evidence was found in the right hemisphere of a posterior-anterior movement along the sylvian fissure. Also, the left hemisphere N1m sources were all represented more posterior than the right hemisphere N1m sources.