Medial globus pallidus

The medial globus pallidus (or internal, GPi) is one of the output nuclei of the basal ganglia (the other being the substantia nigra pars reticulata). The GABA-containing neurons send their axons to specific nuclei of the dorsal thalamus (VA and VL), to the centromedian complex and to the pedunculopontine complex.

The efferent bundle is constituted first of the ansa and fasciculus lenticularis, then crosses the internal capsule as the Edinger's comb system then arrives at the laterosuperior corner of the subthalamic nucleus and constitutes the Forel's field H2, then H, and suddenly changes its direction to form H1 that goes to the inferior part of the thalamus. The distribution of axonal islands is widespread in the lateral region of the thalamus. The innervation of the central region is done by collaterals.