The Basal Ganglia

The basal ganglia are a group of anatomically closely related subcortical nuclei. Damage to these nuclei does not cause weakness, but can cause dramatic motor abnormalities. The mechanisms by which lesions in the basal ganglia cause clinical symptoms have not been completely elucidated.

Anatomy

(see figure 08) ) ) The striatum (caudate and putamen) receives projections from wide regions of the neocortex, and projects to the globus pallidus (GP). The nucleus accumbens and the ventral pallidum (vP) are limbic regions of the caudate and GP, respectively (figure 12). The striatum also projects to and the pars reticulata of the substantia nigra (SNpr), which is not shown in the illustrations. SNpr and GPi are closely related structures with similar connections. The globus pallidus and SNpr projects to the thalamus (VA/VL), which projects back to cortex. In addition to a motor loop shown in detail in figure 13 that projects to motor cortical structures , several other cortico-striato-pallido-thalamic-cortical loops have been defined anatomically (two are shown in figure 14, the dorsolateral frontal and orbitofrontal (limbic) loops). Additionally, there is a sub-circuit from the globus pallidus to the subthalamic nucleus, and back to the globus pallidus shown in Figure 13.

Clinical syndromes:

Parkinsonism

Loss of dopaminergic neurons in the substantia nigra (pars compacta) that normally project to the striatum is associated with rigidity, bradykinesia, tremor, and loss of postural reflexes. that characterize Parkinson's disease.

Hemiballismus (hemichorea)

Hemiballismus is associated with damage to the contralateral subthalamic nucleus of Luys.

Huntington's chorea

an hereditary disease characterized by progressive dementia and chorea, is associated with atrophy of the caudate nucleus. Strokes of the caudate, however, rarely cause chorea.