  Simultaneous estimates of the activity in the left and right auditory cortex
of five normal human subjects were extracted from Multichannel
Magnetoencephalography recordings. Left, right and binaural stimulation were
used, in separate runs, for each subject. The resulting time-series of left and
right auditory cortex activity were analysed using the concept of mutual
information. The analysis constitutes an objective method to address the nature
of inter-hemispheric correlations in response to auditory stimulations. The
results provide a clear evidence for the occurrence of such correlations
mediated by a direct information transport, with clear laterality effects: as a
rule, the contralateral hemisphere leads by 10-20ms, as can be seen in the
average signal. The strength of the inter-hemispheric coupling, which cannot be
extracted from the average data, is found to be highly variable from subject to
subject, but remarkably stable for each subject.
