Evoked synchronization/desynchronization of cortical electrical activity in response to facial stimuli during...

Evoked EEG theta and alpha rhythm synchronization/desynchronization responses to facial stimuli were studied in healthy subjects (n = 35) in an experiment involving formation of a set to an emotionally negative facial expression. The magnitude of the evoked theta activity synchronization response in the group of subjects with the plastic type of set was greater and the latent period was shorter than in the group with the rigid type of set. These differences were particularly clear in the temporal and parietal-occipital areas. A sufficiently high level of the phasic theta potentials synchronization response, reflecting the level of activity of the corticohippocampal feedback system during the perception of facial stimuli, was required for rapid substitution of the set to facial expressions. In subjects with plastic sets, the evoked low-frequency alpha potentials response was apparent as synchronization, while that in subjects of the "rigid" group consisted of desynchronization. These results were interpreted in terms of the concept of Klimesch (2007) that the evoked alpha potentials synchronization response is a measure of inhibition in cognitive activity. The alpha potentials synchronization response reflects the process of inhibitory control, which plays an important coordinating role in organizing the plastic properties of the set in relation to its inhibition when it ceases to correspond to new stimuli. The involvement of the tonic and phasic forms of cortical activation, mediated by the corticohippocampal and frontothalamic brain systems, in the functional organization of the cognitive set to an emotionally negative facial expression is discussed.