Relevance of EEG alpha and theta oscillations during task switching.

In a task switching design, we investigated the question whether long-range theta coupling primarily reflects top-down control processes. Switch and stay trials did not differ with respect to memory load or global working memory (WM) demands. The results revealed significantly stronger theta coupling (in a range of 4-7 Hz) between prefrontal and posterior regions during switch as compared to stay trials. Power differences, reflecting more local effects, were largest in the upper alpha band (10-13 Hz) and over posterior brain areas, possibly reflecting long-term memory activation. The conclusion of the present study is that long-range coherent oscillatory activity in the theta band reflects top-down activation rather than global WM functions.