Role of the occipito-temporal Theta rhythm in hand visual identification

Neuroimaging and EEG studies have shown that passive observation of the full body and of specific body parts is associated with: 1) activity of an occipito-temporal region named the Extrastriate Body Area (EBA), 2) amplitude modulations of a specific posterior ERP component (N1/N190), and 3) a theta-band (4-7Hz) synchronization recorded from occipito-temporal electrodes compatible with the location of EBA. To characterize the functional role of the occipito-temporal theta-band increase during the processing of body-part stimuli, we recorded EEG from healthy participants while they were engaged in an identification task (match-to-sample) of images of hands and non-body control images (leaves). In addition to confirming that occipito-temporal electrodes show a larger N1 for hand images compared to control stimuli, cluster-based analysis revealed an occipito-temporalcluster showing an increased theta power when hands are presented (compared to leaves) and show that this theta increase is higher for identified hands compared to non-identified ones while not being significantly different between not identified non-hand stimuli. Finally, single trial multivariate pattern analysis revealed that time-frequency modulation in the theta band is a better marker for classifying the identification of hand images than the ERPs modulation. The present results support the notion that theta activity over the occipito-temporal cortex is an informative marker of hand visual processing and may reflect the activity of a network coding for stimulus identity.