Human oscillatory brain activity within gamma band (30-50 Hz) induced by visual recognition of non-stable postures.

Our principal finding from this study is that there were changes at the level of brain electrical activity (EEG) during cognitive tasks while subjects were instructed to visually recognize non-stable postures of a computer animated human body model. In particular, there was clear enhancement of the amplitude within the gamma band (30-50 Hz) activity associated with visual recognition of non-stable postures at fronto-central and parietal areas in all subjects. The Morlet's wavelet transform was applied to examine the change of time-frequency (TF) energy within a range of 1-70 Hz frequencies range as a function of experimental tasks. There was a high energy burst within the 35-45 Hz TF cluster at fronto-central and parietal areas when subjects visually recognized non-stable postures. Experimental evidences were provided demonstrating that EEG activity recorded during visual recognition of non-stable postures was related to specific judgement of postural instability. In a series of control experiments, additional evidences were provided to justify the specific sensitivity of EEG 40-Hz activity to the act of visual recognition of postural instability. The contamination of muscle activity in the reported EEG results during perceptual tasks was also ruled out. Our findings are consistent with the notion of existence of specialized neural detectors (predictors) for specific postures and goal-oriented behavior. However, the functional significance and precise cognitive and neurophysiological mechanisms predicting the existence of these detectors remain to be explored.