FIGURE 3.2 The effect of cocaine and amphetamine.

NOTE: NAc = nucleus accumbens; VTA = ventral tegmental area.

In addition to the reward pathways, the human brain contains multiple circuits that are involved in the processing of emotion, learning, and conditioning. These "emotional circuits" are adaptive survival circuits; they assign significance (e.g., dangerous, edible, desirable) to individuals, things, and events in the world, and then regulate the functioning of both the input and output circuits of the brain to produce adaptive responses, including escape, approach, and aggression. Connections between brain circuits mediating emotional states and those that mediate the encoding of memories underlie the development of memories with strong or weak emotional components. If strong enough, such memory can be quite simple, as when a child burns his or her finger, and a single experience will dominate subsequent behavior. However, most memories are complex and involve multiple emotional components.