Functional inertia reveals history-dependent organization of large-scale brain dynamics

Abstract

The brain does not process the present in isolation. Its responses are shaped by the accumulating weight of prior states, yet existing frameworks treat large-scale brain dynamics as sequences of transient configurations, leaving the constraining influence of history implicit in how models are specified rather than measured directly. Here we define functional inertia as the rate of change of an accumulated latent state and make it measurable through an inertial state-space model. Applied to resting-state fMRI in 160 healthy controls and 151 individuals with schizophrenia, functional inertia organizes brain activity into three recurrent regimes, and patients redistribute their time across them in a way that tracks negative symptom severity. The same measure carries opposite consequences in the two groups, linked to better cognition in controls and to more severe symptoms in patients, because what inertia means depends on the accumulated configuration it operates from. The same contextual logic holds across circuits, where stronger inertia tracks greater symptom negative severity in integrative hubs and lower severity in sensory pathways, resolving the longstanding tension between reports of excessive rigidity and reports of excessive volatility in schizophrenia. These findings position functional inertia as a multilevel constraint on brain reorganization, and the accumulated past as a dimension of brain function that can be measured rather than assumed.