Presence of strong harmonics during visual entrainment: A magnetoencephalography study

► Participants viewed a visual stimulus that flickered at 18 Hz during MEG. ► Synchronization was examined at the fundamental, 2nd, 3rd, and 4th harmonic frequencies. ► Strong event-related synchronization (ERS) was found in all frequency bins. ► There was large individual variation in participants' strongest harmonic response. ► Higher harmonic responses had partially distinct cortical loci from the fundamental.