striatum

The striatum is a subcortical structure of the forebrain and a principal component of the basal ganglia. In humans and other primates it comprises the caudate nucleus and putamen, collectively known as the neostriatum; the ventral striatum, including the nucleus accumbens and olfactory tubercle, lies ventral to these structures.

Anatomy and connections: The striatum receives extensive glutamatergic input from nearly all areas of the cerebral cortex and thalamus, and projects mainly GABAergic output to the internal segment of the globus pallidus and the substantia nigra pars reticulata. The dorsal striatum (caudate and putamen) is strongly linked to motor control and habit learning, while the ventral striatum is involved in reward, motivation, and goal-directed behavior.

Cellular composition: The principal neurons are medium spiny neurons, which are GABAergic and form the major input-output channels. Interneurons, including parvalbumin-positive and cholinergic neurons, modulate local circuits. Dopamine from the substantia nigra pars compacta and ventral tegmental area modulates striatal activity via D1- and D2-family receptors, shaping synaptic plasticity in direct and indirect pathways.

Function and disease: The striatum integrates cortical signals to influence movement, learning, and decision making. Dysfunction of striatal circuits is implicated in Parkinson's disease, Huntington's disease, obsessive-compulsive disorder, addiction, and other neuropsychiatric conditions. Treatments such as dopaminergic therapy and, in some cases, deep brain stimulation target striatal or pallidal structures.