Loss of consciousness under anesthesia increasingly constrains brain activity to follow the brain's physical structure, collapsing hierarchical cortical organization across scales. This effect was observed with three different anesthetics—propofol, sevoflurane, and ketamine—and was reversed by electrically stimulating the central thalamus, which also restored behavioral signs of arousal. Stimulating the ventral lateral thalamus did not produce these effects, showing specificity. The findings identify distributed brain signatures of consciousness that are orchestrated by particular thalamic nuclei.
Transcranial direct current stimulation (tDCS) applied to the prefrontal cortex alters the dynamic organization of functional connectivity in the primate brain, with effects depending on the state of consciousness. In awake macaques, cathodal tDCS disrupted the repertoire of connectivity patterns, increased structure-function correlation, decreased Shannon entropy, and favored transitions toward anatomically based patterns. Under deep sedation, anodal tDCS significantly altered brain pattern distribution and reduced structure-function correlation. The stimulation also modified dynamic connectivity arrangements typically associated with consciousness and unconsciousness. These findings suggest that prefrontal tDCS can modulate brain dynamics differently in conscious and unconscious states, offering insights into mechanisms relevant to disorders of consciousness.