It’s been called a “thunderclap” headache – a sudden intense pain that’s the hallmark of a rare but usually deadly type of stroke called a subarachnoid hemorrhage (SAH). If the initial event doesn’t kill, as many as 30% of patients will suffer further strokes within two weeks from a blockage caused by blood vessels in spasm. Now, a neurosurgeon is hoping to someday prevent these secondary strokes by decoding – and harnessing - the frenzied molecular messages produced by a stroke-choked brain.