Exploring flicker light mechanisms: No evidence that MEG signal diversity relates to subjective experience

Stroboscopic flashing light with white noise can induce a mild altered state of consciousness (ASC), with some effects similar to sensory deprivation and moderate doses of psychedelic substances. However, effective clinical utilisation of this white noise flicker light (WNFL) requires understanding the underlying mechanisms. Here, neural correlates and predictors of WNFL experience are explored as potential mechanisms. Expectancy effects were explored using a novel sham condition. Thirty participants underwent trait measures before three 10-minute MEG scans: baseline, then counterbalanced conditions of 15Hz WNFL and sham, where steady light without noise was falsely described as WNFL using imperceptible high frequencies. Outcome measures included MEG signal diversity, consciousness alteration and imagery. Potential predictors included trait absorption, expectancy and previous ASC experience. Imagery and signal diversity remained stable during WNFL exposure and were higher than in the sham condition. Signal diversity was not significantly related to any outcome or predictor variables. Ratings of consciousness alteration were predicted by expectancy ratings and greater than similar flicker studies without audio. Pattern of results was comparable to previous reports of psychedelic experience. WNFL induces an ASC involving increased visual imagery and complexity of neural signalling that are stable over time. Expectancy does not explain all WNFL effects but may shape aspects of the experience. The addition of audio to flicker light interventions may enhance consciousness alteration and clinical outcomes. WNFL shows promise as a research tool for investigating consciousness and as a clinical tool for screening and preparing individuals for more intensive ASC-based therapies.