The nucleus accumbens is a collection of neurons within the striatum. It plays an important role in reward, laughter, pleasure, addiction, fear, and the placebo effect. Each half of the brain has one nucleus accumbens. It is located where the head of the caudate nucleus and the anterior portion of the putamen meet just lateral to the septum pellucidum. The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum, which is part of the basal ganglia. The nucleus accumbens can be divided into two structures: 1) the nucleus accumbens core; 2) the nucleus accumbens shell. These structures have different morphology and function.
The main neuronal cell type that is found in the nucleus accumbens is the medium spiny neuron. The neurotransmitter produced by these neurons is gamma-aminobutyric acid, one of the main inhibitory neurotransmitters of the central nervous system. These neurons are also the main projection or output neurons of the nucleus accumbens. While 95% of the neurons in the nucleus accumbens are medium spiny GABA-ergic projection neurons, other neuronal types are also found such as large aspiny cholinergic interneurons.