Poster F52, Tuesday, March 27, 8:00-10:00 am, Exhibit Hall C
An MEG study of lexico-semantic processing in sentence comprehension: A Representational Similarity Analysis
Lin Wang1,2, Ole Jensen3, Gina Kuperberg1,2; 1Department of Psychiatry and the Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA, 2Department of Psychology, Tufts University, Medford, MA, USA, 3Centre for Human Brain Health, University of Birmingham, Birmingham, UK
In EEG/MEG, semantic processing is classically indexed by a smaller N400(m) to expected than unexpected words between 300-600ms. MEG source localization suggests that one source of this effect is the left anterior superior temporal cortex. Intracranial recordings, however, report sources in the medial temporal region. The current MEG study used a representational similarity analysis to identify brain regions distinguishing between semantically expected and unexpected critical words. Twenty-six Chinese participants read 240 high-constraining sentences, ending with either expected or unexpected sentence-final words (SFWs). We extracted the spatial pattern of neural activity to SFWs within two regions of interest (ROIs): left superior temporal cortex and left medial temporal region (left parahippocampus + hippocampus + fusiform). Within each ROI, we correlated the spatial pattern between all possible pairs of (a) expected SFWs (b) unexpected SFWs (c) expected – unexpected SFWs. We then averaged these spatial patterns to construct two time series of R values, reflecting shared spatial patterns for expected SFWs (within-expected pairs), unexpected SFWs (within-unexpected pairs), as well as between the unexpected and expected SFWs (between-condition pairs). Within the superior temporal ROI, between 300–600ms after SFWs onset, spatial similarity was greater for within-unexpected than both within-expected and between-condition pairs. However, within the medial temporal ROI, spatial similarity was greater for both within-unexpected and within-expected pairs than for the between-condition pairs. We suggest that both the superior temporal and medial temporal regions were engaged in processing semantically unexpected words, whereas the medial temporal region was selectively engaged in processing semantically expected words.
Topic Area: LANGUAGE: Semantic