The image shows dopaminergic pathways of the human brain in normal condition (left) and Parkinsons Disease (right). Red Arrows indicate suppression of the target, blue arrows indicate stimulation of target structure. (Pallidothalamic connections visible but not labeled, as red line from GPi to THA.)
The ansa lenticularis is composed of fibers that pass from the ventral aspect of the globus pallidus and sweep around the posterior limb of the internal capsule. They connect with the fibers of the lenticular fasciculus in the Field of Forel (H) to form the thalamic fasciculus.
The lenticular fasciculus (also known as Forel's Field H2) is composed of fibers that pass from the internal part of the globus pallidus, through the posterior limb of the internal capsule, around the zona incerta. These fibers connect with the fibers of the ansa lenticularis in the Field of Forel (H) to form the thalamic fasciculus.
The thalamic fasciculus (also known as Forel's Field H1) is formed by the fibers of the ansa lenticularis and the lenticular fasciculus that merge in the Field of Forel (H). The fibers of this fasciculus then travel to the thalamus and primarily terminate in the ventral anterior nucleus and ventral lateral nucleus. Some fibers travel to the interthalamic nuclei.