Figure 1.

Parallel cortico-striatal-thalamic-cortical circuitry. Two types of pyramidal neurons project from the cortex to the striatum: the intratelencephalic (IT) neuron, which project ipsilaterally and bilaterally to the cortex and striatum; and the pyramidal tract (PT) neuron, which projects ipsilaterally to the striatum, but also projects to the ipsilateral thalamus, subthalamic nucleus (STN), mesencephalon (including the substantia nigra pars compacta, SNpc) and spinal cord. IT and PT neurons project to both subtypes of GABAergic striatal efferent neurons: the striatonigral (SN) neuron, which directly connect the striatum with the output structures of the basal ganglia, which are the substantia nigra pars reticulata (SNpr) and the internal segment of the globus pallidus (iGP); and the striatopallidal (SP) neuron, which connect indirectly with the output structures by a relay through the external segment of the globus pallidus (eGP) and the STN. This scheme shows only the characteristic parallel processing of the basal ganglia, but there is also a substantial level of convergent integration of cortico-striatal projections, more specifically from reciprocally connected cortical regions, such as the motor and somatosensory cortical areas. Dysfunction of cortico-striatal-thalamic-cortical circuitry involving motor and somatosensory cortical areas seem to determine the PLMS and akathia components of RLS.