Normally, enhanced oscillatory activity at the delta frequency during cognitive tasks may be an indicator of attention and task demand [32], [33]. Recently, it was also found that phase synchronization in the delta and also in the theta frequency range correlated positively with the task performance in the Identical Picture test in young adults and negatively in older adults [30]. In our case, the oscillatory activity at the delta frequency can be paralleled to the Go-P3 and NoGo-P3, in terms that Go-P3 has been proposed to reflect response-related cognitive process, whereas the NoGo-P3 has been linked to response inhibition [37], [38], [39]. Thus, this low frequency phase synchronization in Go trials during the first time interval after stimulus onset (0–300 ms) showing centro-parietal brain activity distribution is in accordance with the concept about attentional load and is related to response execution mentioned above, whereas this low frequency synchronization in NoGo trials is apparently needed to suppress undesirable response. This assumption is in accordance with ERP studies showing relation of the P3-NoGo component and anteriorization of this component to response inhibition,
