People across cultures and throughout history report spiritual experiences that involve a sense of union transcending the ordinary self, but their neural mechanisms are poorly understood. Using an individualized guided-imagery task, the authors compared brain activity during personally meaningful spiritual experiences with that during stressful and neutral-relaxing experiences. During spiritual experiences, the left inferior parietal lobule showed reduced activity compared to neutral-relaxing experiences, suggesting this region contributes to perceptual processing and self-other representations. Compared to stress cues, spiritual cues reduced activity in the medial thalamus and caudate, regions linked to sensory and emotional processing. The findings point to neural mechanisms underlying broadly defined, personally experienced spirituality.
Ketamine and psychedelics can alter markers of synaptic density, which may relate to their abuse liability and potential therapeutic effects in substance use disorders. A scoping review of 84 studies found mixed results for ketamine: single or repeated doses under basal conditions produced inconsistent synaptic changes in the hippocampus and prefrontal cortex, but a single dose counteracted stress-related reductions in these markers, and repeated dosing also reversed stress effects. Psychedelics generally increased synaptic markers, though results varied by agent. The heterogeneity likely stems from differences in methods, drugs, sex, and marker types.