Altered states of consciousness (ASC) can occur spontaneously, be evoked by physical or physiological stimulation, induced by psychological means, or caused by diseases. Psychological and neurobiological approaches reveal four dimensions characterizing ASC: activation, awareness span, self-awareness, and sensory dynamics. Neurophysiologically, different states of consciousness arise from compromised brain structure, transient changes in brain dynamics (disconnectivity), and neurochemical and metabolic processes. Environmental stimuli, mental practices, and self-control techniques can also temporarily alter brain functioning and conscious experience.
Psilocybin, a hallucinogenic substance, alters the internal representation of time by increasing the loss rate of the internal duration representation. In two double-blind, placebo-controlled experiments—one with 12 subjects receiving graded doses and another with 9 subjects receiving a very low dose—participants repeatedly reproduced time intervals between 1.5 and 5 seconds. The parameter kappa from the 'dual klepsydra' model was used to assess effects. At 90 minutes after intake, psilocybin significantly increased kappa, indicating a higher loss rate of internal time representation. These findings may relate to qualitative changes in subjective time during altered states of consciousness.