[Contribution of spontaneous EEG to understanding cognitive functions]

Probability mapping of amplitude and coherence based on spectral analysis of the on-going EEG turned out to yield information on the cooperation of brain areas during cognitive processes. The method is based on comparing these two parameters during the performance of a mental task with the respective values of the EEG at rest before and after the task. For each of six frequency bands, spanning and entire EEG spectrum, the signs of significant changes of these parameters at the recording electrodes (19) and between all recording sites (19 x 18) are entered into schematic maps, representing the brain as seen from both sides and from the top. The results have proved to be largely task-specific for mental processes in both groups and individual studies. They are considered as electrical manifestations of differential attention. Since they may encompass EEG periods of even several minutes, these maps allow observations of average EEG characteristics even in complex, long-lasting mental accomplishments. The usefulness of the method is illustrated by four examples: doing mental arithmetic, listening to and composing music, simultaneous interpretation and contemplating and memorizing pictures.