Functional brain networks can be studied through homological cycles—topological objects that capture mesoscopic structure in weighted correlation networks. A new method, homological scaffolds, compactly represents these cycles and makes them amenable to standard network analysis. Applied to resting-state fMRI data from 15 healthy volunteers given placebo or psilocybin, the homological structure of brain activity changed dramatically after psilocybin, producing many transient, low-stability cycles and a few persistent ones absent under placebo.
Brain activity can be viewed as exploring a landscape of different activity patterns over time, shifting between stable states of functional connectivity that support various mental processes. In a study using fMRI data from healthy participants given intravenous psilocybin (the active compound in magic mushrooms), researchers analyzed how this dynamical landscape changes during the psychedelic state. They found that a connectivity state linked to the fronto-parietal control system became strongly destabilized, while transitions toward a globally synchronized state increased. These changes suggest the psychedelic state biases the brain toward global integration at the cost of local network segregation, offering a mechanistic perspective on the subjective psychedelic experience and potential guidance for pharmacological interventions in neuropsychiatric disorders.