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Dynamics of early MEG activation elicited by semantic incongruences in the left temporal and inferior-frontal cortex
Abstracts of the 45th Annual Meeting of the Society for Psychophysiological Research, Psychophysiology, 42 (S1), 115
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Traditional views on brain correlates of semantics link semantic access to slow responses at 350-400 ms. To study early dynamics related to semantic stimulus properties, we recorded, in passive oddball paradigm, MEG responses to short spoken phrases where the second word was either congruent or incongruent with the first one. The acoustic, phonological and psycholinguistic features were strictly controlled for, and the contrasts were counterbalanced within and across subjects. Responses to the same critical words were obtained also outside of semantic context. We found that regardless of their acoustic features, semantically incongruent stimuli elicited an MMN-like response at ~120-160ms after the critical word onset. The same words did not produce such deflection in semantically legal context. The responses were maximal at left temporal and inferior-frontal sites. The temporal activation preceded the frontal one by ~16ms. Further, the inferior-frontal activity showed more substantial modulation by the semantic context, whereas the temporal source seemed more affected by acoustic stimulus features. No late response dynamics (>350ms) were found that would reflect the semantic modulation in this non-attend passive design; this suggests a role of attention in generating the later shifts. The results suggest that the earliest brain processes of semantic context integration may occur at ~120 ms after the onset of spoken words in the left interior frontal and superior temporal cortex.