The dynamics of electroencephalographic (EEG) activity in continuous compensatory tracking tasks were analyzed by independent component analysis (ICA) and time-frequency techniques. In one-hour sessions, 72-channel EEG was recorded while a healthy volunteer attempted to use a trackball to keep a drifting disc in a bulls-eye in the center of screen. Disc trajectory was converted into a moving measure of disc error. Local minima (perigees) indicated moments when the disc started to drift away

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... the center. Subject performance was indexed by root mean square disc error in a 20s epoch centered on each perigee, high error generally indicating drowsiness. Maximally independent EEG processes and their equivalent dipole source locations were obtained using the EEGLAB toolbox (http://sccn.ucsd.edu/eeglab). Component activations were epoched in 5s time intervals time locked to perigees. Following disk perigees during (drowsy) periods of high disk error, significant spectral changes were observed. One of the 70 independent components was located in or near primary visual cortex. During periods of poor (drowsy) performance, it had increased mean tonic alpha/theta activity, with a further phasic alpha/theta increase following perigees [1, 2]. At the same time, low alpha activity of a second component located in or near cingulate gyrus increased, and 10-30 Hz EEG activity of a third component in the left somatomotor cortex increased briefly. The alpha activity of the somatomotor component persisted through the following distance maximum. These spatiotemporal phenomena were consistently observed across three sessions within subjects. Thus, event-related EEG brain dynamics can be detected and modeled in a continuous behavioral task without impulsive event onsets.