With regards to the time course of Per2 expression, it is possible that early Per2 induction during the first week after aneurysm rupture is responsible for protection against ischemia and early brain injury in SAH, while dynamics in Per2 expression that occur later during the course of the disease may not be as relevant—however, the data as of yet do not allow this conclusion. The gene discussed is PER2; the disease is aneurysm.