Effects of 18.5 Hz Auditory and Visual Stimulation on EEG Amplitude at the Vertex
Recently, audio-visual stimulation (AVS) has been proposed to be effective as an adjunct to EEG biofeedback (neurofeedback) therapy, when used as a "priming stimulus" to activate desired cortical frequencies. Since standard neurofeedback therapies for ADD/HD involve training subjects to enhance activity in the 13-21 Hz bandpass, we hypothesized that this activity could also be enhanced by AVS at a constant frequency in this range. Further, we hypothesized that auditory or visual stimulation alone might induce an entrainment effect. EEG was recorded from fifteen college students under the following conditions: (A) auditory stimulation alone, with eyes open; (B) auditory stimulation alone, with eyes closed; (C) visual stimulation alone, with eyes closed; (0) both auditory and visual stimulation, with eyes closed. An e-yes-closed and eves-open baseline condition were recorded prior to the first session. An ANOVA on the differences between the four stimulation conditions and baseline revealed no significant differences between the conditions, so the averages of all four conditions were analyzed as a single group. A significant increase was observed in the 13-21 Hz band (p = 0.045). This increase was of greater magnitude and significance in the narrower 16-20 Hz band (p = 0.008). When this band was analyzed in half-Hz intervals, a prominent peak was observed at 18.5 Hz (p = 0.001). Applying this same analysis to the individual conditions suggested that the eyes-closed conditions with auditory or visual stimulation alone had more generalized effects throughout the 16-20 Hz band. These results support the hypothesis that AVS entrains endogenous EEG rhythms, and suggest a possible adjunctive role for AVS in EEG biofeedback therapies. However; the relatively weak generalization to frequencies adjacent to the stimulation frequencies suggest that variable-frequency AVS might be more effective at activating the desired range of frequencies within a given bandpass.