The basal ganglia are a group of subcortical nuclei, most of which are located in proximity to the thalamus and hypothalamus. These regions and their white matter pathways connect to the cortex and indirectly to descending pyramidal and other spinal cord pathways that modulate motor and cognitive programs ( Figs 1.6-1. and
16-2 ). There is no dedicated basal ganglia-spinal tract, and the so-called final common pathway for basal gangliar motor function involves the corticospinal pyramidal tract and the lower motor neuron (see C.ha.p.te,r...1.5 ). Although they are highly complex, these anatomical connections have been schematized in block diagrams in order to test specific hypotheses related to hypokinesia and hyperkinesia (.Fig 16-3 ). The specific nuclei of primary focus are the caudate nucleus and putamen, collectively known as the striatum; the globus pallidus (both internal and external segments, termed GP i and GPe ); the subthalamic nucleus; and the substantia nigra (pars compacta and pars reticulata).
Figure 16-1 Transverse section of a human brain with basal ganglia identified. CN = caudate nucleus, P = putamen, GP = globus pallidus, T = thalamus = internal capsule anterior limb, I£ = internal capsule posterior limb.
Figure 16-2 Cross section of a human midbrain with the black band of dark melanin-rich substantia nigra (SN) and the pyramidal tract that lies anteriorally.
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