Clinical neurophysiology of stroke

Stroke constitutes the third most common cause of death and the leading cause of acquired neurologic handicap. During ischemic stroke, very early after the onset of the focal perfusion deficit, excitotoxicity triggers a number of events that can further contribute to tissue death. Such events include peri-infarct depolarizations and spreading depolarizations (SDs) within the ischemic penumbra. SDs spread slowly through continuous gray matter at a typical velocity of 2-5mm/min. SDs exacerbate neuronal injury through prolonged ionic breakdown and SD-related hypoperfusion (spreading ischemia). Scalp EEG alone is not yet sufficient to reliably diagnose SDs. Hyperexcitability occurs in parallel, both in the acute and chronic phases of stroke. Stroke is a common cause of new-onset epileptic seizures after middle age and is the leading cause of symptomatic epilepsy in adults. The last part of this chapter is dedicated to noninvasive neurophysiologic techniques that can be used to promote stroke rehabilitation. These techniques mainly include repetitive transcranial magnetic stimulation and tDCS. These approaches are based on the concept of interhemispheric rivalry and aim at modulating the imbalance of cortical activities between both hemispheres resulting from stroke.