The medial segment of the globus pallidus sends fiber projections to which of the following?

An infant was born with Leigh disease caused by a maternal inheritance pattern with abnormal mutations in mitochondrial DNA. The patient displays central nystagmus with rotary and horizontal components, nuclear opthalmoplegia, and irregular respiration. As the child begins to walk, truncal ataxia and intention tremor become evident. Magnetic resonance imaging (MRI) reveals symmetric lesions in the caudate putamen and globus pallidus. The medial segment of the globus pallidus sends fiber projections to which of the following?

(A) caudate nucleus
(B) pars compacta of the substantia nigra
© subthalamic nucleus (of Luys)
(D) ventral anterior nucleus of the thalamus
(E) ventral posterior lateral nucleus of the thalamus

Explanation:

(D) The medial segment of the globus pallidus projects to the ventral anterior as well as ventral lateral, dorsomedial, centromedian, and parafascicular nuclei of the thalamus. The medial segment also gives rise to pallidotegmental and pallidohabenular fibers. The caudate nucleus (choice A) and the putamen provide input to the globus pallidus and do not receive pallidal projections. The pars compacta of the substantia nigra (choice B) and subthalamic nucleus (of Luys; choice C) receive projections from the lateral segment of the globus pallidus. The ventral posterior lateral nucleus of the thalamus (choice E) receives projection fibers from the dorsal column-medial lemniscal system, as well as fibers from the anterolateral system. It does not receive fibers from the globus pallidus.