The research question:
What is the impact of audiovisual stimulation (AVS) in the electrocortical activity of different brain regions?
Audio visual stimulation (AVS) aims to affect the brain pattern activity, by stimulating the central nervous system via specific optic and acoustic signals. AVS has been shown to have potential therapeutic value in a broad spectrum of diseases, ranging from pain relief to amelioration of cognitive disabilities. The present study aimed to assess the effects of AVS in different brain areas during and shortly after the stimulation, using electroencephalography (EEG). Furthermore, the researchers examined whether repeated sessions of AVS could have an additive effect on specific parameters. The outcome of the study validated that AVS can indeed affect the brain’s electrical activity, and improve the coordinated function of the two hemispheres, both during and after the stimulation. Repeated AVS sessions lead to a progressive increase of the effects of stimulation, but the results were dependent on the specific brain area and frequency examined.
All 6 participants received 25 sessions of audiovisual stimulation (AVS). EEG recordings were obtained from the period prior (3min), during (20min) and after (3min) the AVS. Electroencephalograms were analyzed both by on line visual control of the ongoing EEG and later by off-line analysis. Analyzed data included total power, relative frequency and powers, and magnitude-squared coherences, as well as the volunteer’s subjective perception of the training process. Extend of the brain wave entrainment was researched through comparison to non-stimulation conditions represented by the period prior to stimulation.
The AVS program stimulated brain at the following frequencies: 17 Hz during the first 3 min followed by fast decrease to 10 Hz and slower decrease to 8 Hz during min 4–8, then fast decrease to 5 Hz during min 8–9, slower decrease to 4 Hz during min 9–10, steady 4 Hz during next 3 min followed by decrease to 2 Hz during min 13, steady 2 Hz during min 14–17, and then stepwise return through 5 Hz, 9 Hz to 15 Hz at min 17–20…Sound beats were produced from three sine wave pulses. One wave was fixed to stable frequency at 280 Hz. Then, a required number of beats per second was controlled by distances of two other frequencies from 280 Hz”
The main purpose of this study was to assess the immediate and short term effects of AVS on the brain activity pattern. Using the specific parameters described above, the AVS lead to direct intense brain wave entrainment, through the increase of spectral powers and coherences around the stimulating frequency bands. The effects were more profound in the occipital regions and in the 4Hz stimulation frequency. Furthermore, repeated AVS training sessions resulted in a progressive increase of the driving response for the 2 and 4 Hz stimulation, but not for the 9 and 17 Hz, in centro-parietal locations. Progress was also made in the interhemispheric synchronization as indicated by coherences. In the short term period after the stimulation, the intense increases of spectral power observed during the AVS quickly fainted, and a few decreases were observed, probably as an opposite reaction to the stimulation. Interestingly, the increased interhemispheric cooperation at the parieto-occipital areas was sustained in the 3 minutes post stimulation period.
“Audio-visual stimulation is a way of external influence of the brain by rhythmic light and sound stimuli. AVS primarily activates brain centers for visual and sound processing.”
“More recently, devices using light and sound at specified frequencies have been used to ‘drive’ the EEG toward certain frequencies. In the last decades audio-visual stimulation has been reported as an effective method for relieving dental anxiety, to induce hypnagogic states, helping to relieve tension and migraine headaches, for therapeutic effect on premenstrual syndrome, to improve behavioral and cognitive functions of learning disabled boys, to alleviate the cognitive dysfunctions in connection with closed head injury, and damages from aneurysms and strokes. Comprehensive review of the AVS effects suggests that AVS is an effective therapeutic tool.”
“Photic stimulation techniques can also be seen as a promising nonpharmacological treatment strategy especially in disorders where guided entrainment of the brain waves or intermediate increase of synchronization of hemispheres is desired. However, let us recall our previous study indicating that, on a long term basis, use of AVS may suppress the cooperation between the hemispheres. Obviously, extensive and very cautious large-scale controlled studies should be performed before any therapeutic application.”
Teplan, M., Krakovská, A., & Štolc, S. (2011). Direct effects of audio-visual stimulation on EEG. Computer Methods and Programs in Biomedicine, 102(1), 17-24.