This study was a preliminary evaluation of biofeedback training of human subjects to control high-frequency EEG responses in the 35- to 45-Hz (40-Hz) and 21- to 31-Hz ranges. A total of 22 adult males divided into three groups were successfully trained for increases or suppression of 40-Hz EEG, or increases of 21- to 31-Hz EEG. Dissociation of rates of 40-Hz EEG recorded from scalp leads and 40-Hz EMG responses from prominent muscle contaminators, and partial dissociation of 40-Hz and 21- to 31-Hz EEG responses were noted. After biofeedback training, 8 subjects demonstrated increase and suppression of 40-Hz EEG without feedback. No consistent descriptors of subjective experiences accompanying EEG changes were reported by subjects in any of the groups. The study suggests the utility of biofeedback procedures in research on high-frequency EEG activity.

Two groups of eight adults successfully trained with biofeedback for increases in 40-Hz EEG responses in left or right hemispheres also demonstrated significant 40-Hz EEG increases during baseline periods, and increases in the contralateral hemisphere during training periods. No changes in heart rate, 40-Hz EMG, or 21- or 31-Hz beta, alpha, or theta EEG occurred over training days. Three subjects returning for additional training demonstrated suppression of 40-Hz EEG. A group of four subjects experiencing daily bidirectional training produced substantial within-session control of 40-Hz EEG but no changes over days. Data from posttraining tests without feedback for successful subjects in both groups indicated significant control of 40-Hz EEG responses in the initial parts of these sessions, and some correlated changes in other EEG responses. Measures of successful subjects' experiences during training and control tests indicated awareness of changes in subjective concomitants of EEG responses. This study suggests further strategies for research on behavioral correlates of EEG activity.

Maintenance of conditioning of 40-Hz EEG activity was investigated in six adults 1 to 3 years after they had experienced biofeedback training to increase 40-Hz EEG. Subjects were first retrained to alternately increase and suppress 40-Hz EEG. All six subjects achieved a preset performance criterion in 16-20 minutes. Five of these subjects also subsequently demonstrated significant control of 40-Hz EEG without feedback. The sixth subject did not demonstrate control after 76 minutes and four sessions of attempted retraining with feedback. Transfer of 40-Hz EEG control to a problem-solving task was tested in all subjects in a final session. Cognitive test items were presented and subjects were instructed to alternately increase and suppress 40-Hz EEG while solving the problems. Rates of 40-Hz EEG in suppression periods during problem solving wer significantly greater than during suppression periods without problems. No significant differences in problem-solving performance were found comparing 40-Hz increase and suppression periods. This study supports previous research suggesting an association between 40-Hz EEG and mental activity, and suggests methods for further study of transfer of EEG biofeedback effects.