Motor Functions of the Basal Ganglia

Definition The basal ganglia consist of four prominent nuclei, which are interposed between the cerebral cortex and the lower centers of the brain stem and spinal cord. These nuclei include the: striatum (caudate, putamen, ventral striatum including nucleus accumbens) globus pallidus internal (GPi) and external (GPe) segments substantia nigra pars compacta (SNpc) and pars reticulata (SNpr) subthalamic nucleus (STN) Most of the inputs and outputs of the basal ganglia arise from or go to the cortex either directly or indirectly through the thalamus. Thus, the basal ganglia form something of a side loop or detour in the relation of the brain to behavior. As a result, determining the function of the basal ganglia has been more difficult than for brain areas that more directly respond to impinging sensory stimuli (See sensory cortex) or elicit distinct motor outputs (See motor cortex). While the basal ganglia mediate many nonmotor functions including cognition, emotion, and sensory processing, they have long been regarded as primarily involved with movement. Lesions of the basal ganglia cause motor deficits. The disorders most associated with the basal ganglia – such as Parkinson's disease (PD), dystonia, and Huntington's disease(HD) – are considered movement disorders, even though other functions can be disrupted in these patients (e.g. sleep in PD, mood in HD, cognition in both PD and HD). Within the basal ganglia, the putamen is most directly associated with movement and receives abundant cortical input. From the putamen, impulses flow through the GPi/GPe, STN, and SNpr to the thalamus. The SNpc sends a large dopaminergic projection to the striatum (See dopamine). The SNpc is the nucleus most degenerated in PD.