subthalamicus

The subthalamicus, commonly known as the subthalamic nucleus (nucleus subthalamicus), is a small, lens-shaped cluster of neurons located in the subthalamus, a region of the diencephalon. It lies ventral to the thalamus and medial to the internal capsule, forming an integral part of the basal ganglia circuitry that regulates movement.

Anatomy and connections: The subthalamic nucleus receives excitatory input from the cerebral cortex via the hyperdirect pathway and inhibitory input from the external segment of the globus pallidus (GPe). It projects excitatory glutamatergic outputs to the internal segment of the globus pallidus (GPi) and to the substantia nigra pars reticulata (SNr). Through these connections, the STN helps modulate thalamic activity and influence motor output. In addition to motor circuits, the STN participates in cognitive and limbic networks through broader connections with the cortex and other basal ganglia structures.

Function and clinical relevance: The subthalamic nucleus plays a key role in the regulation of voluntary movement and action selection. Disturbances in its activity can contribute to motor disorders. Lesions of the STN can produce hemiballismus, a violent, flinging movement of the limbs contralateral to the lesion. Deep brain stimulation targeting the STN is an established treatment for symptoms of Parkinson’s disease and, in some cases, other movement disorders, often allowing reduced medication dosages and improved motor function.