Recreational ketamine use, primarily administered by smoking, is associated with dose-dependent psychiatric symptoms and cognitive deficits. Heavier use correlates with greater psychological distress, especially anxiety and hostility. Users show reduced accuracy on high-load working memory tasks and have smaller left hippocampal volume, most notably in the hippocampal-amygdaloid-transition-area. Functional connectivity between this region and several brain networks is increased and aligns with NMDA-receptor distribution. These findings suggest that chronic, smoking-administered ketamine use selectively affects hippocampal subregions and related circuitry, potentially explaining working memory impairments.
During nonrapid eye movement (NREM) sleep, consciousness fades as the brain's dynamic functional connectivity changes. Using simultaneous EEG-fMRI recordings in 12 healthy men, the study examined two aspects of dynamic connectivity: mean (dFCmean), reflecting stable network integrity, and variance (dFCvar), indicating instability of information transfer. As sleep deepened, dFCmean decreased progressively across waking and NREM stages (N0~N1 > N2 > N3), while dFCvar peaked during N2 stage (N0~N1 < N3 < N2), suggesting unstable whole-brain synchronizations. In N3 stage, overall network integration was disrupted, with lowest dFCmean and elevated dFCvar. The findings suggest that consciousness dissipates when network specificity breaks down alongside increasing variability of information exchange.