Hypnosis reduces activity in the default mode network (DMN), a set of brain regions active during rest and linked to self-awareness and task-independent thinking, while increasing activity in prefrontal attentional systems. Using brain imaging and subjective measures during passive visual stimulation, the authors found that the state of attentional absorption after a hypnotic induction was associated with these neural changes. Hypnosis and spontaneous conceptual thought at rest were both subjectively and neurally distinct, offering insight into the hypnotic state and its neural basis.
Ketamine rapidly reduces depressive symptoms in treatment-resistant major depressive disorder. Using brain imaging and dynamic causal modeling, researchers analyzed neural excitation/inhibition interactions in the primary somatosensory cortex of 18 unmedicated patients and 18 healthy controls during a somatosensory task. Patients were scanned at baseline, 6-9 hours after ketamine infusion, and 6-9 hours after placebo. A shift in neural dynamics toward a stable region of the Poincaré diagram—requiring increased excitatory and inhibitory coupling—predicted symptom improvement specifically after ketamine, not placebo. This drug-specific neural shift may serve as a biomarker for treatment response.
Both chronic cannabis use and psychotic disorders are linked to abnormalities in how the brain processes visual attention. Using resting-state fMRI, connectivity was measured in the visual and dorsal attention networks of people with early psychosis who did or did not use cannabis, and healthy controls who did or did not use cannabis. Patients with a history of cannabis use showed increased connectivity in the dorsal attention network (134%) and between the visual and dorsal attention networks (285%) compared to non-using controls. In patients who used cannabis, connectivity in these networks correlated with visual hallucinations and with severity of cannabis dependence. The findings suggest that disrupted connectivity in these networks may play different roles depending on cannabis use.
Modest previous cannabis use blunts the acute behavioral and neurophysiological effects of ∆9-THC, the main psychoactive ingredient in cannabis. In a double-blind, placebo-controlled challenge, abstinent modest users (average 24.5 lifetime joints) showed worse cognitive performance and stronger right hemispheric brain activation than non-users, regardless of whether they received ∆9-THC or placebo. Acute ∆9-THC caused transient anxiety and psychosis-like symptoms in all participants, with stronger effects in non-users. Non-users under placebo activated specific brain areas for tasks while deactivating others, an opposite pattern to that seen in non-users under ∆9-THC and in cannabis users under placebo. Among non-users, more severe drug-induced symptoms and cognitive impairments correlated with greater neurophysiological changes.