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Abstract:
Psychophysiological research suggested that the mismatch
negativity (MMN) is generated by a temporofrontal network
subserving change detection processes and an attention switch
toward environmental changes. The present study addresses the
functional role of the frontal lobes in deviancy processing by
systematically varying the degree of pitch deviancy. ERPs were
continously recorded from 64 electrodes in 13 subjects. In a second
session with the same subjects fMRI measures were obtained at 3T
from eight axial slices. When tested under MR background noise
conditions large and medium but not small deviants elicited a
robust MMN, indicating that the latter could not be detected in
such conditions. Consistent with this finding, significant
activations in the superior temporal gyri (STG) bilaterally and the
right frontoopercular cortex were found for large and medium
deviants. In temporal regions the signal change was larger for
large compared to medium deviants suggesting that change detection
processes are subserved by the STG. For the right frontoopercular
cortex the opposite pattern was observed, medium deviants generated
a larger signal change than large deviants. This finding does not
support the view of an attentional switch mechanism reflected in
the frontal MMN generator but rather points to other mechanisms
modulating change detection, such as amplification/contrast
enhancement of the deviance detection system or sequencing the
stream of the incoming sounds.
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