Photic driving evoked by intermittent photic stimulation is an already long known effect in the human brain. It is usually characterized in averaged data by an ongoing oscillation showing frequency entrainment and resonance phenomena during the course of the stimulation. In addition to its widespread use in epilepsy, there are several other (newer) areas of application, including, for example, dementia, migraine, and Parkinson’s disease. In order to gain a better understanding of the generation mechanisms of the photic driving effects, we looked at the ongoing oscillations in the single-trial EEG.

EEG was recorded during visual flash stimulation within the alpha and beta band with eight stimulation frequencies between 7.8 and 23 Hz. 14 healthy volunteers (7 female, 24.6±3.8 years) participated in the study. Time-frequency analysis was performed for both, averaged and unaveraged data using a complex Morlet wavelet.

Entrainment and resonance phenomena could be shown for both, averaged and unaveraged data. In contrast to ongoing oscillations during stimulation in the averaged signal, we found transient event patterns (bursts) in the unaveraged data.

We showed that continuous oscillations in averaged data during photic driving consist of bursts in single-trial EEG. This can explain already described amplitude fluctuations in the averaged data. These new single-trial findings have the potential to describe and understand intra- and inter-individual differences in the human brain in healthy individuals and patients, and to define new biomarkers for diagnosis and therapy.