An EEG/fMRI study of gamma-band oscillatory activity during ambiguous perception J Castelhano1, C Duarte1, E Rodriguez2, M Castelo-Branco1 |
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1IBILI- Visual Neurosciences Laboratory, Faculty of Medicine, University of Coimbra, Portugal |
| Previous EEG studies have suggested a functional role for increased Gamma-band activity during object perception. The neural sources of this oscillatory response during perceptual decision concerning ambiguous stimuli remain elusive. Here we have recorded simultaneous EEG/fMRI signals during a visual perception task using ambiguous stimuli. Data were acquired from 10 healthy subjects that performed a forced choice discrimination task between Mooney categories (prototypical upright and inverted faces, prototypical guitars and scrambled versions) stimuli. EEG MR gradient and pulse artifacts were corrected offline using Independent Component Analysis. Epochs were obtained locked to the stimuli and event-related potential (ERP) measures, time-frequency analysis and fMRI informed source localization were performed. Behavioural data show that subjects discriminate between categories with high performance levels (>75%). We replicated the typical N170 peak and found oscillatory activity was enhanced within the high beta/low gamma range (20-40Hz) locked to the perception moments. The latencies of oscillatory activity peaks were used as general linear model (GLM) predictors for fMRI source localization. We found that different gamma sources are related to perception, spanning from temporal areas to parietal and frontal regions. |
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