Tonic, phasic, and transient EEG correlates of auditory awareness in drowsiness.
During drowsiness, human performance in responding to above-threshold auditory targets tends to vary irregularly over periods of 4 min and longer. These performance fluctuations are accompanied by distinct changes in the frequency spectrum of the electroencephalogram (EEG) on three time scales: (1) during minute-scale and longer periods of intermittent responding, mean activity levels in the (< 4 Hz) delta and (4-6 Hz) theta bands, and at the sleep spindle frequency (14 Hz) are higher than during alert performance. (2) In most subjects, 4-6 Hz theta EEG activity begins to increase, and gamma band activity above 35 Hz begins to decrease, about 10 s before presentations of undetected targets, while before detected targets, 4-6 Hz amplitude decreases and gamma band amplitude increases. Both these amplitude differences last 15-20 s and occur in parallel with event-related cycles in target detection probability. In the same periods, alpha and sleep-spindle frequency amplitudes also show prominent 15-20 s cycles, but these are not phase locked to performance cycles. (3) A second or longer after undetected targets, amplitude at intermediate (10-25 Hz) frequencies decreases briefly, while detected targets are followed by a transient amplitude increase in the same latency and frequency range.
Makeig
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Naval Health Research Center, San Diego, CA 92186-5122, USA. scott@cpl_mmag.nhrc.navy.mil
Jung
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D000161:Acoustic Stimulation; D000328:Adult; D001309:Auditory Threshold; D001364:Awareness; D004569:Electroencephalography; D006801:Humans; D015203:Reproducibility of Results; D012890:Sleep / Q000502:physiology; D012894:Sleep Stages; D013826:Theta Rhythm; D013997:Time Factors