Fig. 1.

The 10/20 international electrode placement system. The used electrode sites are indicated by bold circles for the Auditory oddball task (upper half) and the checker board reversal task (bottom). Each electrode position is characterized by one or more letters to identify the underlying brain area and a number or letter to identify the hemisphere (even number: right hemisphere, odd number: left hemisphere, letter z: midline). The letters F, C, T, P and O stand for frontal, central, temporal, parietal and occipital. The letters FP refer to a prefrontal electrode (frontopolar). Electrodes anterior to the frontal electrodes are named anterior frontal (AF). Electrodes positioned between frontal and central electrodes, central and parietal electrodes, parietal and occipital electrodes, parietal and temporal electrodes and frontal and temporal electrodes are labeled FC (frontocentral), CP (centroparietal), PO (parieto-occipital), TP (parietotemporal) and FT (frontotemporal) respectively