State-Dependent Brain Stimulation for Visual Neurorehabilitation: Principles and Applications

The effects of Transcranial Magnetic Stimulation (TMS) depend on stimulation parameters such as intensity, location, frequency, and duration. In clinical practice, these parameters are often adapted from studies carried out in healthy individuals. However, in this narrative review, we indicate that the impact of TMS is also highly state-dependent, meaning it is influenced by the excitability of the targeted brain region at the time of stimulation. This state-dependency complicates the translation of findings from healthy individuals to clinical populations, as neurological disorders often alter brain states, limiting the applicability of standard stimulation protocols. To address this challenge, stimulation parameters must be chosen within a framework that accounts for the interaction between external stimulation and the brain's internal state. Such an approach enhances the specificity of interventions, allowing for targeted modulation of neural populations by manipulating brain states prior to stimulation. State-dependent TMS has shown promise in conditions like cortical blindness and amblyopia, where tailored approaches based on the brain state associated with the condition have facilitated more precise and effective treatments. We advocate that integrating state-dependent knowledge tailored to the specifics of visual disorders alongside judicious selection of stimulation parameters holds the potential to establish a comprehensive paradigm for future investigations.