Changes in electrical activity of the brain with vigilance.

The relationship between EEG and vigilance was studied in subjects performing tasks of differing complexity over a 15 h period by examining the structural changes of the EEG as vigilance deteriorates. Calculation of canonical variates indicated that two directions explained the changes in vigilance, though one direction was dominant across subjects and tasks, and likely to reflect decreased arousal. The second direction indicated some evidence for a second underlying change in the EEG related to vigilance in some subjects particularly in the more complex task, and this would reflect mechanisms other than drowsiness. The relationship between EEG and vigilance was modelled by fitting a linear function of EEG variables to the proportion of missed responses. The coefficient of multiple correlation was significant for most subjects, and the relationship is likely to represent changes in arousal. The most useful discriminator of worsening vigilance common to both tasks was beta activity (14-21 Hz).