but one of the discoveries in the 1980s is that the thalamus also goes directly into the amygdala. that means by the time the auditory stimulus is reaching the amygdala and activating those fear responses, it hasn't even begun to have its impact on the cortex yet. >> what i like about this finding which joe came up with, it really explains the james insight. off direct pathway that gives you the immediate emotional response and then you have an indirect pathway to the cerebral cortex that allows you to contemplate and think about it and have the conscious sense of it. the feeling state. >> the direct pathway is quick and dirty. gets there fast but not very precise. a bomb goes off in the room, we don't know what it is, it's already made us freeze and start to run away and stuff. by the time it gets to the cortex you only size the sound and the quality and all of that. but by that time your amygdala's already kicked in and got you out of the room. >> rose: do you develop a fear of insects and snakes? what causes you to have anxiety about those two creatures? >> you have it from the

and this involves the basal ganglia and the region called the thalamus. but in the 60s there were remarkable series of discoveries. the first was the presence of a substance called dopamine within the brain. and particularly in the basal ganglia. and then in rapid succession, the evidence that it was depleted in brains of patients who were at autopsy with parkinson's. these two discoveries led to the attempts to replace that substance by giving a drug called levadopa, a precursor of dopamine. and taken and absorbed and actually reaches the brain. and this was viewed as a cure. it was a matter of time, though, that the other foot dropped, so to speak. and began to realize that with, after the honeymoon period of a number of years, often patient was develop involuntary movements. we call them diskin esias, or they would have what we call motor fluctiations where the medicine would wear off abruptly. and these combination of motor fluctuationsing sometimes failure to respond and the diskinesias would be very disruptive of movement. and this called for really