The Telencephalon

The basal ganglia are a group of subcortical nuclei, of various origins, located at the base of the telencephalon and in the upper part of the midbrain. They are strongly interconnected with the cerebral cortex, thalamus, and brainstem, as well as different other areas of the brain. They are associated with a variety of functions, including control of voluntary movements, procedural learning, habit learning, eye movements, cognition, and emotion. The main components of the basal ganglia—as functionally defined—are the striatum, both the dorsal striatum (caudate nucleus and putamen) and the ventral striatum (nucleus accumbens and olfactory tubercle), the globus pallidus, the ventral pallidum, the substantia nigra, and the subthalamic nucleus. Each of these components has a complex internal anatomical and neurochemical organization. The most important component, the striatum (dorsal and ventral), receives input from many areas of the brain beyond the basal ganglia, but only sends output to other components of the basal ganglia. The pallidum receives input from the striatum and sends inhibitory output to various motor areas. The substantia nigra is the source of striatal input of the neurotransmitter dopamine, which plays an important role in basal ganglia function. The subthalamic nucleus receives input mainly from the striatum and cerebral cortex, and projects onto the globus pallidus. The basal ganglia are of great importance for normal brain function and behavior. Their dysfunction results in a wide range of neurological conditions including behavioral and movement control disorders. Behavioral ones include Tourette's syndrome, obsessive-compulsive disorder, and addiction. Movement disorders include Parkinson's disease, which involves degeneration of dopamine-producing cells in the substantia nigra, Huntington's disease, which mainly involves damage to the striatum, dystonia and, more rarely, hemiballismus.