As indicated by its name, the subthalamic nucleus is located below the thalamus; dorsally to the substantia nigra and medial to the internal capsule. The subthalamic nucleus is lenticular in form and of homogeneous aspect. It is made up of a particular neuronal species having rather long ellipsoid dendritic arborisations, devoid of spines, mimicking the shape of the whole nucleus. The subthalamic neurons are "fast-spiking pacemakers" spiking at 80 to 90 Hz. There are also about 7,5% of GABA microneurons participating in the local circuitry. The subthalamic nucleus receives its main afference from the lateral pallidum. Another afference comes from the cerebral cortex (glutamatergic), particularly from the motor cortex, which is too much neglected in models. A cortical excitation, via the subthalamic nucleus provokes an early short latency excitation leading to an inhibition in pallidal neurons. Subthalamic axons leave the nucleus dorsally. Except for the connection to the striatum (17.3% in macaques), most of the principal neurons are multitargets and ffed axons to the other elements of the core of the basal ganglia. Some send axons to the substantia nigra medially and the medial and lateral nuclei of the pallidum laterally (3-target 21.3%). Some are 2-target with the lateral pallidum and the substantia nigra (2.7%) or the lateral pallidum and the medial(48%). Fewer are single target for the lateral pallidum. If one adds all those reaching this target, the main afference of the subthalamic nucleus is, in 82.7% of the cases, the lateral pallidum (external segment of the globus pallidus. While striatopallidal and the pallido-subthalamic connections are inhibitory (GABA), the subthalamic nucleus utilises the excitatory neurotransmitter glutamate.