The connexions of the striatum and globus pallidus: synthesis and speculation

Recent findings on the afferent and efferent connexions of the striatum (the caudate nucleus and putamen) and globus pallidus have been summarized in an orderly sequence. The striatum receives afferent fibres from three main sources, the cerebral cortex, the intralaminar nuclei of the thalamus and the midbrain; the major features of each of these pathways are outlined. The striatum sends efferent fibres to the globus pallidus and the substantia nigra, and the two segments of the globus pallidus in turn project upon the subthalamic nucleus and upon the thalamus and midbrain tegmentum. Through the thalamus the major influence of the striopallidum is upon the motor area of the cerebral cortex, and it is suggested that through the midbrain tegmentum there may also be a descending influence upon the spinal cord. These findings from light microscopical investigations are synthesized with observations made in electron microscopic studies of the striatum and globus pallidus. On the basis of present knowledge of their structure and connexions attention is drawn to several marked similarities between these parts of the basal ganglia and the cerebellum.