Psychedelic drugs like psilocybin, found in magic mushrooms, produce profound changes in consciousness by decreasing activity and connectivity in key brain hub regions. Using functional MRI, researchers observed that psilocybin reduced cerebral blood flow and BOLD signal, especially in the thalamus, anterior cingulate cortex (ACC), and posterior cingulate cortex (PCC). Decreased activity in the ACC and medial prefrontal cortex (mPFC) predicted the intensity of subjective psychedelic effects. Psilocybin also reduced positive coupling between the mPFC and PCC. These findings suggest that psychedelics work by dampening the brain's connector hubs, leading to a state of unconstrained cognition.
LSD produces marked changes in brain activity that correlate with its psychological effects. Increased blood flow in the visual cortex, decreased alpha power there, and an expanded functional connectivity profile of the primary visual cortex strongly correlated with visual hallucinations, suggesting that intrinsic brain activity influences visual processing more during the psychedelic state. Decreased connectivity between the parahippocampus and retrosplenial cortex correlated strongly with ego-dissolution and altered meaning, indicating this circuit's role in maintaining the self and processing meaning. Different imaging metrics showed strong relationships, allowing firmer inferences about their functional significance.
Psilocybin, a classic psychedelic drug, may enhance the vividness and visual imagery of positive autobiographical memories. In a small study of ten healthy participants, functional magnetic resonance imaging scans showed that under psilocybin, compared to placebo, recollection of positive memories produced additional visual and sensory cortical activations in the late phase of recall. Participants also rated memories as more vivid and visually rich after psilocybin, and higher vividness correlated with greater subjective wellbeing at follow-up. These findings suggest psilocybin could be useful in psychotherapy for facilitating recall of salient memories or reversing negative cognitive biases.
Lysergic acid diethylamide (LSD) in microgram doses produces profound, sometimes life-changing experiences and is a uniquely powerful psychoactive substance. In the first modern neuroimaging study of LSD, marked changes in brain blood flow, electrical activity, and network communication patterns were observed. These changes correlated strongly with the drug's hallucinatory and consciousness-altering properties. The findings have implications for understanding the neurobiology of consciousness and for potential applications of LSD in psychological research.