TASK-INDUCED ASYMMETRY OF THE AUDITORY-EVOKED M100 NEUROMAGNETIC FIELD ELICITED BY SPEECH SOUNDS

The auditory evoked neuromagnetic fields elicited by synthesized speec h sounds (consonant-vowel syllables) were recorded in six subjects ove r the left and right temporal cortices using a 37-channel SQUID-based magnetometer. The latencies and amplitudes of the peaks of the M100 ev oked responses were bilaterally symmetric for passively presented stim uli. In contrast, when subjects were asked to discriminate among the s ame syllabic stimuli, the amplitude of the M100 increased in the left and decreased in the right temporal cortices: Single equivalent curren t dipole modeling of the activity elicited by all stimulus-types local ized to a well-circumscribed area in supratemporal auditory cortex. Th e results suggest that attentional modulation affects the two supratem poral cortices in a differential manner. Task-conditioned attention to speech sounds is reflected in lateralized supratemporal cortical resp onses possibly concordant with hemispheric language dominance.