  A question of cooperative effects in auditory brain processing on various
space- and time-scales is addressed. The experimental part of our study is
based on Multichannel Magnetoencephalography recordings in normal human
subjects. Left, right and binaural stimulations were used, in separate runs,
for each subject. The resulting time-series representing left and right
auditory cortex activity provide a clear evidence for two levels of neuronal
cooperation. One is the local hemispheric collective response, termed M100 for
its maximum at around 100ms after a stimulus onset. Its only global
characteristics turn out to be time-locked to a stimulus, however, which means
that the detailed neuronal evolution is largely stochastic. This, together with
the $1/f$ character of the corresponding power spectrum indicates
self-organized criticality as an underlying mechanism. The second level is
communication between the two hemispheres with clear laterality effects: as a
rule, the contralateral hemisphere leads by $\sim$10ms. Mutual information
analysis points to a direct information transport as a way of this
communication.
