. >> rose: let me begin with gerry fischbach. tell me about this notion of neurological disorders and the neural systems they involved. >> i want to begin by talking about stroke because it points out how vulnerable this brain is. as eric said, it's the most complex organ in the body, probably the most complex phenomenon that we know in the universe. it's made up of over 100 billion cells and every one of these cells is working hard. they need to generate enormous energy to maintain their signaling, their ability to talk to each other in the brain. and for this they need oxygen. and the oxygen is brought to them by the blood supply. you can put a tourniquet around your arm and cut off the blood flow for a minute, for several minutes. many of us have had our blood pressure taken and once in a while the physician walks out of the room and forgets that the cuff is still inflated. and even though you may be squeezing your hand, you're find for up to ten, 15 minutes or longer. but if you cut off the blood supply to the brain for secon