The subthalamic nucleus is a cluster of neurons found within the brain of most mammals, including humans. It is part of the basal ganglia, a collection of neuronal nuclei that assist in the coordination of voluntary movement. Synchronized firing by the subthalamic nuclei and by neighboring neurons of the globus pallidus function as the pacemaker of the entire basal ganglia, and are necessary for stable control of motion in the limbs. Increased abnormal activity of the subthalamic nucleus occurs in movement disorders like Parkinson's disease and the rarer disease called hemiballismus.
The basal ganglia of the brain includes the subthalamic nucleus along with related regions like the striate and the substantia nigra. All of these nuclei moderate pathways in the brain that are important to the control of voluntary movement. They are excitatory, which means that they work by exciting neurons to fire electrically. Along with the cerebellum, which controls motion through inhibition, the basal ganglia is one of the two main regions concerned with executing voluntary movement. The subthalamic nuclei are anatomically close to the thalamus and communicate with it, hence their name.
Functionally, the subthalamic nucleus is closely associated with the globus pallidus, a nearby region of the basal ganglia. These neuronal groups are pacemakers, which means that they fire in sync with each other and thus excite any neurons to which they are connected. In the primate basal ganglia, the subthalamic nuclei receive feedback from neurons of the cerebral cortex that direct voluntary movement. Thus it is part of the pathway connecting the planning of a movement in the cortex with the parts of the brain that control its muscular execution.
Abnormal activity by the subthalamic nucleus has also been implicated in the motor dysfunction of Parkinson's disease. Researchers have noted that destruction of this area due to stroke and other injuries typically improved movement in patients. For Parkinson's treatment, some neurosurgeons have developed a procedure designed to mimic the good effects of this damage to the subthalamic nucleus. Called deep-brain stimulation, it is accomplished by the surgical placement of electrodes in the basal ganglia, using electrical pulses to disrupt select neuronal activity in certain areas. Some clinical trials indicated the procedure was more effective medical treatment in patients with severe Parkinson's symptoms.
Hemiballismus is a very rare motion disorder characterized by violent flinging movements of the arm on one side of the body. It usually results from damage to the subthalamic nucleus, although cell death in other parts of the basal ganglia can cause milder forms of its symptoms. Any neurological disease that attacks the nuclei that effect voluntary movement can potentially cause hemiballismus. It can result from oxygen deprivation due to stroke or trauma. The severity of hemiballismus depends on the extent of cellular damage.