Scientists have studied the main source of serotonin in the brain -- the dorsal raphe nucleus (DRN). By studying how activating the brain's 'serotonin center' affects awake animals for the first time, they found that serotonin from the DRN activates brain areas that affect behavior and motivation. Results show that DRN serotonin stimulation causes activation of the cerebral cortex and the basal ganglia, brain areas involved in many cognitive functions.