Consciousness depends on how tightly brain function follows the brain's physical wiring. Using MRI scans, researchers measured structure-function coupling across spatial scales in people who were unconscious from anesthesia or brain injury and in people under psychedelics (LSD or ketamine). During loss of consciousness, function more closely tracked the brain's structural connections, a signature that could distinguish behaviorally similar brain-injured patients and detect covert consciousness. In contrast, psychedelics decoupled function from structure, and this decoupling correlated with physiological and subjective scores. The findings suggest that connectome harmonic decomposition reveals how neuromodulation and network architecture jointly shape consciousness.
Consciousness arises from how the brain's structural wiring shapes its dynamic activity. By decomposing resting-state fMRI data into harmonic modes of the human structural connectome, a generalizable signature of lost consciousness emerges—whether from anesthesia or brain injury—while a reversed signature characterizes psychedelic states induced by LSD or ketamine, reflecting decoupling of function from structure. This connectome harmonic approach discriminates between behaviorally indistinguishable brain-injured patients and tracks covert consciousness, linking neurobiology to conscious experience.
In weekly cannabis users, cannabis suppresses the brain's anticipatory reward response to money, and cannabidiol (CBD) does not moderate this effect. The adolescent reward circuitry is not differentially sensitive to the acute effects of cannabis on reward anticipation. This double-blind, placebo-controlled, crossover study with 23 adults (26-29 years) and 24 adolescents (16-17 years) used functional magnetic resonance imaging (fMRI) to measure brain activity during a monetary reward anticipation task after inhaling cannabis with tetrahydrocannabinol (THC), THC plus CBD, or placebo. THC acutely reduced reward anticipation activity in the ventral striatum and right insula compared with placebo. THC plus CBD also reduced activity in these regions. The effects were the same in adolescents and adults.