UC San Diego

Research is presented on the altered sensory and cognitive processing as assessed by event-related potential analysis of electroencephalographic data during states of meditation in long-term meditators and due to the effects of psilocybin, a naturally occurring serotonin receptor agonist with hallucinogenic properties and the literature on the neurophysiological correlates to meditation are reviewed. In a passive auditory oddball paradigm the rare tones and distracters are shown to evoke increased sensory processing as indexed by increases in the amplitudes of the N1 and P2 event-related potential components. The distracter stimuli are shown to evoke a later P3a component and increases in frontal theta power associated with attentional engagement. Meditation causes a significant reduction in the P3a amplitude and frontal theta power to distracting stimuli implying the disengagement of attentional networks from ongoing sensory processing. Psilocybin is shown to cause enhanced early sensory processing of visual stimuli as indexed by the P1 component. This psilocybin-induced alteration is shown to be especially prominent in the brain's response to distracting stimuli in a visual target detection paradigm. Psilocybin is also shown to decrease intermediate object- recognition processing as indexed by the N170 event- related potential. While N170 amplitudes are shown to be increased due to the perception of illusory contours, psilocybin induces a brain state where fewer additional resources are recruited to the perception of illusory contours. Later P3 amplitudes associated with detection and response-related processing as well as distracter processing are shown to be significantly reduced by psilocybin, supporting the notion that attentional networks are disengaged from ongoing sensory processing. Psilocybin inhibits the increase in frontal theta activity associated with the perception of illusory contours and visual distracters, adding further support to the model of attentional disengagement. A preliminary model of psilocybin-induced changes in neurophysiology and integrative comments on the significance of the similarities and differences between the effects of meditation and psilocybin on the brain's attentional systems are provided