Dynamic stiffening of brain states: a neurodynamic framework of functional adaptation, impaired transitions, and neuromodulation

Contemporary approaches in systems neuroscience describe the brain as a nonlinear dynamical system capable of adopting multiple transient functional configurations. Within this perspective, functional impairment may concern not only the properties of individual brain states but also the capacity to transition between them when contextual demands change. We propose a theoretical framework centred on dynamic stiffening, defined as impaired context-dependent accessibility of transitions between functional brain configurations. This phenomenon is not restricted to oscillatory activity or to a single neurobiological mechanism. The progressive stabilisation of an initially adaptive response represents one possible pathway, alongside alterations in connectivity, plasticity, or regulatory processes. Thalamocortical interactions constitute one plausible substrate, while EEG provides an accessible, though indirect, means of investigating neural reconfiguration. The central experimentally testable prediction is that, when cognitive or environmental demands require neural reconfiguration, individuals exhibiting the hypothesised dynamic-stiffening phenotype will show reduced probabilities or increased latencies of transitions towards functionally appropriate neural configurations compared with suitable controls, even when the overall repertoire of observed configurations remains relatively preserved. Alterations in state diversity, persistence, and recovery dynamics are considered complementary rather than necessary features. The framework outlines experimentally testable predictions and conditions for falsification, distinguishing adaptive stability, impaired transition accessibility, and excessive instability. Finally, it proposes that neurofeedback and neuromodulation could be investigated as potential means of modifying transition dynamics, while recognising that their causal and therapeutic relevance remains to be established.