Optimal parameters for propagating gamma brain waves using flickering lights in human

Background Sensory stimulation with 40 Hz flickering light could entrain gamma oscillations leading to decreased amyloid β burden. However, the optimum parameters of a light source to promote brain gamma activity in humans have not suggested yet. We performed the study to investigate the optimal intensity and frequency of the flickering light stimulus (FLS) in young adults. Method We measured electroencephalography (EEG) during the FLS presented. We compared the event‐related synchronization (ERS) values of entrained gamma waves between four different luminance intensities (10, 100, 400, and 700 cd/m2) at 10 different flickering frequencies from 32Hz to 50Hz with an interval of 2Hz. Each frequency condition was comprised of 10 times repetition of 2‐sec with inter‐stimulus interval (ISI). We also examined the severity of six adverse effects in both experiments. Using the Granger causality, we compared the propagation of gamma waves in visual cortex to other brain regions between different luminance intensities and flickering frequencies. Result Entrained gamma activity started after the FLS onset, lasted during the FLS, and diminished after the FLS offset which was observed most highly at parietal area and steadily decreased from the parietal to the frontal area. Lights of higher luminance intensities (700cd/m2 and 400cd/m2) entrained stronger and more widely spread gamma waves than those of lower luminance intensities (100cd/m2 and 10cd/m2). Lights flickering at 34Hz ∼ 38Hz entrained stronger and more widely spread beyond visual cortex than those flickering at 40Hz ∼ 50Hz. Conclusion Optimal frequency of FLS for entraining brain gamma activity in human may be different from those in animals. Higher luminance with lower gamma frequency stimulus are effective to propagate the gamma activity to the frontal area.