Hazardous nature of high-temporal-frequency strobe light stimulation: neural mechanisms revealed by magnetoencephalography

Individuals in contemporary society are continually exposed to various visual stimuli. Such stimulation, especially when high in temporal frequency, may sometimes cause unexpected events such as photosensitive seizures. Although many studies have demonstrated that high-temporal-frequency (>3 Hz) visual stimulation can yield hazardous responses in the CNS, the mechanisms by which it does so are still unclear. We therefore investigated the mechanisms of neural perturbation by high-temporal-frequency strobe light stimulation with high-temporal-frequency resolution (4–20 Hz with an interval of 2 Hz) using magnetoencephalography with high temporal and spatial resolution. We show that (1) three temporal dipole phases (phases 1, 2 and 3, by time course) can be identified in the visual evoked magnetic fields (VEF's) across stimulation frequencies based on the goodness-of-fit values for equivalent current dipole estimation and horizontal dipole directions, (2) the dipole moment of VEF's is correlated with autonomic nervous system activity in phases 1 and 2, (3) some temporal stimulation frequencies enhance magnetic responses in phases 1, 2 and 3, and (4) these frequencies are harmonically related, with a greatest common divisor frequency (fundamental frequency) of approximately 6.5 Hz. Our clarification of the temporal frequency characteristics of VEF's will contribute to understanding of the potential hazardous effects of high-temporal-frequency strobe light stimulation in the CNS.