BET differences among simultaneous evoked frequency band responses during early-stage visual processing distinguish...

In this work, we attempt to extend to the schizophrenia's research the evidence that different frequency bands may emerge from different sources during early-stage visual processing, in a mental state-specific manner, while subjects are passively viewing a visual stimulus. We applied standard pattern reversal stimulation (checker-board), a task with low cognitive demands, coupled to a dense EEG recording system to estimate the neural correlates of the evoked theta, alpha, beta, beta1, and gamma frequency band responses by means of brain electrical tomography (BET). After filtering the evoked activity using different band-passes, a very different picture about the current sources during P100 will emerge. The results showed notable differences between the two groups. In healthy subjects we localized the significances in the anterior cingulate, caudate nucleus, thalamus, precuneous region, and superior parietal that were more active for gamma band. In patients with schizophrenia differences occupy the hippocampus, parahippocampus, thalamus, midbrain, precuneus, and superior parietal regions. Most areas were more active for gamma band except precuneous and superior parietal region more active for theta and alpha frequency band. These sets of regions, in both groups, reflect events that are parallel to and partly independent of the P100 component, while in the schizophrenia, these regions have been previous linked to the major symptoms of the disease. We concluded that this result provides important evidence indicating that the proposed method is able to differentiate electrophysiological patterns in healthy subjects from those in patients with schizophrenia.