Stroke remains a leading cause of human disability. Important gains have been realized in the setting of acute ischemic stroke, where thrombolytic and catheter-based reperfusion therapies can substantially improve long-term behavioral outcomes. However, most patients with a new stroke are not eligible for such therapies because of delays in diagnosis or hemorrhagic etiology, for example, and many who are treated nonetheless have substantial long-term disability. Additional classes of poststroke therapy are needed.