Characterization of Altered Waking States of Consciousness in Healthy Humans

Altered waking states of consciousness and its underlying functional organization have gained increasing interest in recent years, i.e. in identifying the neural basis of consciousness. To overcome fundamental shortcomings of current methods to objectively assess the level of consciousness, the investigators propose here to apply a novel and empirically validated measure called 'perturbational complexity index' (PCI) based on the integrated information theory (IIT). This involves a combination of transcranial magnetic stimulation (TMS) and highdensity electroencephalography (hd-EEG) to measure electrocortical responses as distributed cerebral interactions ('integration') and spatiotemporal pattern ('information'). Given the finding of subjectively expanded consciousness as induced here by psilocybin, the investigators hypothesize that the PCI may be higher in such states. This will be the first TMS/hd-EEG study to investigate quantitatively the level of consciousness in a pharmacologically altered waking state of consciousness.