FOS and Cerebral ischemia: A substantial body of literature supports that the entire ipsilateral hemispheric c‐Fos induction outside the infarct core is linked to cortical spreading depolarization,43 a phenomenon brought on by the excessive buildup of glutamic acid in the extracellular fluid after cerebral ischemia, which contributes to the expansion of ischemic infarction beyond the ischemic core.44