Whole-head magnetoencephalographic (MEG) responses
to repeating standard tones and to infrequent slightly
higher deviant tones and complex novel sounds were recorded
together with event-related brain potentials (ERPs). Deviant
tones and novel sounds elicited the mismatch negativity
(MMN) component of the ERP and its MEG counterpart (MMNm)
both when the auditory stimuli were attended to and when
they were ignored. MMNm generators were located bilateral
to the superior planes of the temporal lobes where preattentive
auditory discrimination appears to occur. A subsequent
positive P3a component was elicited by deviant tones and
with a larger amplitude by novel sounds even when the sounds
were to be ignored. Source localization for the MEG counterpart
of P3a (P3am) suggested that the auditory cortex in the
superior temporal plane is involved in the neural network
of involuntary attention switching to changes in the acoustic
environment.
