Extended Amygdala: A Key Component of the Brain Reward System
Historically, the brain reward (pleasure) system was thought to be a series of brain cells and pathways that projected bidirectionally from the midbrain to forebrain, and forebrain to midbrain, and it was called the medial forebrain bundle. A part of the forebrain component of the reward system has been termed the extended amygdala (Heimer & Alheid, 1991) and may represent a common anatomical substrate for acute drug pleasure and the dysphoria associated with compulsive drug use. The extended amygdala is made up of three major structures: the bed nucleus of the stria terminalis (BNST), the central nucleus of the amygdala, and a transition zone in the medial subregion of the nucleus accumbens (shell of the nucleus accumbens; Heimer and Alheid, 1991). Each of these regions shares certain cell types and connections (Heimer and Alheid, 1991), receives information from limbic structures such as the basolateral amygdala and hippocampus, and sends information to the lateral hypothalamus, a brain structure long associated with processing basic drives and emotions.