[PS-2.9] Oscillatory neuronal dynamics of morphological processing: a MEG/EEG study

Fonteneau, E. 1, 2 , Bozic, M. 1, 2 & Marslen-Wilson, W. 1, 2

1 Department of Experimental Psychology, University of Cambridge, UK
2 MRC Cognition and Brain Sciences Unit, Cambridge, UK

The role of gamma-band oscillations (30-80 Hz) in cognitive processing is a matter of intense debate but there is growing evidence from MEG/EEG that synchronisation in oscillatory dynamics reflects the transient coupling and uncoupling of functional networks related to different aspects of language comprehension (Hagoort et al. 2004). Within the neural language system, linguistic complexity engages primarily left lateralised processes, whereas general processing complexity - as indexed by lexical competition - engages a more bilateral network (Bozic et al. 2010). To track the functional role of oscillatory synchrony in these systems we combined magneto-encephalography (MEG) and event-related brain potentials (ERPs) in an auditory study. Participants listened to lists of words that varied on these two core processing dimensions and occasionally performed a 1-back memory task. Linguistic processing complexity was manipulated by the presence or absence of a potential inflectional morpheme (played, trade). General processing complexity was engaged by the presence of onset-embedded lexical competitors (claim, hump). Source estimates were computed with MNE (L2, minimum norm estimates; Hämäläinen et al. 1993) and phase-locking values (PLV; Lachaux et al. 1999) were analysed to determine trial-by-trial covariance between the left posterior superior temporal gyrus (LpSTG) and temporal and frontal regions. Results time locked to the onset of an inflectional morpheme revealed that phase synchrony increased in the gamma-band between LpSTG and left pars opercularis (B44). In contrast, processing an onset-embedded competitor induced synchrony in a network linking the LpSTG and left anterior inferior temporal gyrus. These findings suggest that enhanced cross-cortical interactions between left temporo-frontal cortical areas are necessary for morpho-syntactic functions while connectivity within temporal brain regions may be sufficient to support aspects of general processing complexity.