Location changes enhance hemispheric asymmetry of magnetic fields evoked by lateralized sounds in humans

Auditory mismatch negativity, the brain's change-detection response, has be en shown to be more sensitive than other early auditory cortex responses to the hemispheric specialization of speech processing. The present study use d magnetoencephalography to assess hemispheric differences in cortical evok ed responses during auditory spatial processing. We compared N1m to lateral ized vowels presented with equal probabilities with mismatch fields (MMNm) to rare lateralized noises interspersed in a sequence of frequent midline s ounds. Both N1m and MMNm dipole amplitudes were higher in the hemisphere co ntralaterally to the side of sound lateralization, but this effect was abou t four times bigger in the mismatch paradigm. Moreover, only MMNm dipoles s howed shorter latencies in the hemisphere contralaterally to stimulation. A pparently stimulus changes activate specialized auditory networks more stro ngly than nondeviant events. (C) 2001 Elsevier Science Ireland Ltd. All rig hts reserved.