Modification of Brain Oscillations via Rhythmic Light Stimulation Provides Evidence for Entrainment but Not for Superposition of Event-Related Responses

Abstract

The functional relevance of brain oscillations in the alpha frequency range (8–13 Hz) has been repeatedly investigated through the use of rhythmic visual stimulation. The underlying mechanism of the steady-state visual evoked potential (SSVEP) measured in EEG during rhythmic stimulation, however, is not known. There are two hypotheses on the origin of SSVEPs: entrainment of brain oscillations and superposition of event-related responses (ERPs). The entrainment but not the superposition hypothesis justifies rhythmic visual stimulation as a means to manipulate brain oscillations, because superposition assumes a linear summation of single responses, independent from ongoing brain oscillations. Here, we stimulated participants with a rhythmic flickering light of different frequencies and intensities. We measured entrainment by comparing the phase coupling of brain oscillations stimulated by rhythmic visual flicker with the oscillations induced by arrhythmic jittered stimulation, varying the time, stimulation frequency, and intensity conditions. In line with a theoretical concept of entrainment (the so called Arnold tongue), we found the phase coupling to be more pronounced with increasing stimulation intensity as well as at stimulation frequencies closer to each participant's intrinsic frequency. Only inside the Arnold tongue did the conditions significantly differ from the jittered stimulation. Furthermore, even in a single sequence of an SSVEP, we found non-linear features (intermittency of phase locking) that contradict the linear summation of single responses, as assumed by the superposition hypothesis. Our findings provide unequivocal evidence that visual rhythmic stimulation entrains brain oscillations, thus validating the approach of rhythmic stimulation as a manipulation of brain oscillations.

Superposition model for Steady State Visually Evoked Potentials

“…(8) (9) where H(k) amplitude depends on (w ak -w rk ), d, k, and R k . The difference (w a1 -w r1 ) defines the position of the two graphs.…”

“…However, there is evidence of non-linear behavior in SSVEP signals [9]. Following the former assumption, we propose a model that represents SSVEP signals, as the superposition of the responses in rising and falling edges for each stimulus.…”

Analysis of the photic driving effect via joint EEG and MEG data processing based on the coupled CP decomposition

“…Moreover, the PD effect is also used to study several neurophysiological diseases like Alzheimers, schizophrenia, and some forms of epilepsy. The studies of the PD effect provide evidence for the frequency selectivity of the neural oscillator network [9], [10]. The authors in [11] used the PD effect for the investigation of neurophysiological mechanisms underlying autistic symptoms.…”

Does 10-Hz cathodal oscillating current of the parieto-occipital lobe modulate target detection?

“…Support for this theory comes from studies using EEG and MEG showing rhythmic visual stimulation modulation of alpha oscillations predicts subsequent periodic patterns in target detectability (Mathewson et al, 2014;Spaak et al, 2014;Kizuk and Mathewson, 2017). Furthermore, this phenomenon seems to be due to entrainment of the endogenous alpha oscillation by the rhythmic visual stimuli (Notbohm et al, 2016;Gulbinaite et al, 2017) rather than some aspect of rhythmically presented visual stimulation (for a critical discussion see Keitel et al, 2014).…”