The Physics and Physiology of Electrical Stimulation of the Brain

Electrical brain stimulation plays an important role in surgical planning and in the treatment of epilepsy, movement disorders, and psychiatric disease. Safe and effective application of stimulation and interpretation of results require an understanding of the underlying physics and physiology. This review synthesizes key principles that govern how electrical stimuli interact with brain tissue and how these interactions shape electrophysiological and clinical responses. This includes an introduction to the core physical concepts that support simple models of stimulation-induced electrical fields. This is followed by a description of how the physiology of neural tissues modifies these predictions, complicating the impact of stimulation on the brain. These physical and physiological principles form the basis of interpretation of commonly studied stimulation responses, including functional responses, afterdischarges, seizures, and cortico-cortical evoked potentials. The goal is to clarify how physics and physiology inform stimulation safety and utility while highlighting important limitations in our current understanding of stimulation responses.