Figure 4: Real-time visual feedback on the power of alpha oscillations in brain regions of interest. (a) The subject was provided with a visual gauge of the real-time level of alpha power within the parieto-occipital (PO) region of interest shown in blue in (b). The radius of the light-grey disk in (a) evolved every 500 ms and increased as alpha power decreased during the eyes-open segment of the experimental run. The static, dark-grey disk was an incentive target for the subject. Its radius was indexed to 2 times the average PO alpha power captured during the baseline run acquired at the beginning of the session. (c) shows the ongoing, respective levels of alpha power variation in the two ROIs: prefontal (in green in b) and PO (in blue in b).