The nucleus accumbens (NAcc), also known as the accumbens nucleus or as the nucleus accumbens septi (Latin for nucleus leaning against the septum or as The pleasure center)), is a collection of neurons and forms the main part of the ventral striatum. It is thought to play an important role in reward, pleasure, laughter, addiction, aggression, fear, and the placebo effect.
Ventral Tegmental Area (VTA) is the area that synthesizes dopamine, which then sends to nucleus accumbens. Nucelus accumbens is the pleasure center, and it is stimulated by the neurotransmitter dopamine from VTA. VTA also sends dopamine to prefrontal cortex which regulates and controls these impulses. The locus coeruleus is the area packed with norepinephrine; and when stimulated by a lack of the addictive substance, will drives the person to do anything necessary to obtain a fix.
Limbic System and Other Subcortical Structures – Leaves out the Nucleus Accumbens (they would be approximately in front the hypothalamus in this drawing. The LImbic system is not to be confused with either Limbeck (an awesome band) or the Degobah System, where Yoda lives.