EEG after prolonged mental activity.

The goal of the present study was to investigate the EEG spectral power changes caused by prolonged (6 hours) intensive mental loading consisted of calculation and choice-reaction tasks. The EEGs were analysed both during the tasks performance and in rest periods at the beginning of the work (after subjects had already mastered the tasks) and at the end. The significant increase both of slow (delta, theta) and fast (beta) activities was shown at the end of the work. The observed EEG spectral power changes with time on task were similar during the different tasks performance as well as in the rest conditions indicating the general character of the observed phenomena. These results are interpreted as reflecting the deterioration of general brain state activity caused by prolonged mental work and the simultaneous additional brain activation to provide sufficient vigilance level and successful tasks performance (the subjects being highly motivated).