Differing Event-Related Patterns of Gamma-Band Power in Brain Waves of Fast- and Slow-Reacting Subjects
NAVAL HEALTH RESEARCH CENTER SAN DIEGO CA
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Fast- and slow-reacting subjects exhibit different patterns of circa 40 Hz-band electroencephalogram EEG activity when responding as quickly as possible to auditory stimuli. This result appears to confirm long-standing speculations of Wundt that fast- and slow-reacting subjects produce speeded reactions in different ways, and demonstrates that analysis of event-related changes in the amplitude of EEG activity recorded from the human scalp can reveal information about event-related brain processes unavailable using event- related potential measures. Time-varying spectral power in a selected 35 to 43 Hz gamma frequency band was averaged across trials in two experimental conditions passive listening and speeded reacting to binaural clicks, forming 40 Hz event-related spectral responses. Factor analysis of between-subject event-related spectral response differences split subjects into two near-equal groups comprised of faster- and slower-reacting subjects respectively. In faster-reacting subjects, 40 Hz power peaked near 200 and 400 ms poststimulus in the react condition, whereas in slower-reacting subjects, 40 Hz power just before stimulus delivery was larger in the react condition. These group differences were preserved in separate averages of relatively long and short reaction-time epochs for each group. Gamma band 20-60 Hz filtered event- related potential response averages did not differ between the two groups or conditions. Because of this, and since gamma-band power in the auditory event- related potential is small compared to the EEG, the observed event-related spectral-response features must represent gamma-band EEG activity reliably induced by, but not phase-locked to experimental stimuli or events. EEG, Event- related potential, 40 Hz, Power spectrum.
- Medicine and Medical Research
- Atomic and Molecular Physics and Spectroscopy