title: A bidirectional link between brain oscillations and geometric patterns.
abstract: Like hallucinogenic drugs, full-field flickering visual stimulation produces regular, geometric hallucinations such as radial or spiral patterns. Computational and theoretical models have revealed that the geometry of these hallucinations can be related to functional neuro-anatomy. However, while experimental evidence links both visual flicker and hallucinogenic drugs to upward and downward modulations of brain oscillatory activity, the exact relation between brain oscillations and geometric hallucinations remains a mystery. Here we demonstrate that, in human observers, this link is bidirectional. The same flicker frequencies that preferentially induced radial (<10 Hz) or spiral (10-20 Hz) hallucinations in a behavioral experiment involving full-field uniform flicker without any actual shape displayed, also showed selective oscillatory EEG enhancement when observers viewed a genuine static image of a radial or spiral pattern without any flicker. This bidirectional property constrains the possible neuronal events at the origin of visual hallucinations, and further suggests that brain oscillations, which are strictly temporal in nature, could nonetheless act as preferential channels for spatial information.
authors.affiliation: Université de Toulouse, CerCo, Université Paul Sabatier, 31062 Toulouse, France, CNRS, UMR 5549, Faculté de Médecine de Purpan, CHU Purpan, 31052 Toulouse Cedex, France, and Department of Psychology, University of Rome Sapienza, 00183 Rome, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Mauro
authors.affiliation: Department of Psychology, University of Rome Sapienza, 00183 Rome, Italy.
authors.forename: Antonino
authors.initials: A
authors.lastname: Raffone
authors.affiliation: Université de Toulouse, CerCo, Université Paul Sabatier, 31062 Toulouse, France, CNRS, UMR 5549, Faculté de Médecine de Purpan, CHU Purpan, 31052 Toulouse Cedex, France, and rufin.vanrullen@cerco.ups-tlse.fr.
authors.forename: Rufin
authors.identifier: http://orcid.org/0000-0002-3611-7716
authors.initials: R
authors.lastname: VanRullen
mesh_terms: D000328:Adult; D058256:Brain Waves; D005260:Female; D005425:Flicker Fusion / Q000502:physiology*; D006212:Hallucinations / Q000503:physiopathology; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology
keywords: EEG; flicker; geometric; hallucination; oscillation