Corpus Luysi

CORPUS LUYSI (Luysovotelo; Gr. hypo-thalamicum, s. subthalamicum), an oval nucleus located in the intermediate brain, in the subthalamica region, beneath the nucleus lateralis thalami optici, inside the internal capsule and globus pallidus, above the base of the brain stem and outside the nucleus ruber [see separate table (Bone Marrow), Fig. 1]. In humans it is well delimited and measures 10-13 mm in length, 6-7 mm in width, and 3-4 mm in thickness; its long axis is directed forward and slightly inward. The corpus luysi, having the shape of a biconvex lentil, has two surfaces—dorsal, or upper-inner, and ventral, or lower-outer, two edges—outer and inner, and two ends—anterior and posterior. The dorsal surface is surrounded by a dense capsule of myelinated fibers belonging mainly to the bundle of Forel; these fibers separate the zona incerta from the corpus luysi. The lower surface contacts the internal capsule, in the posterior limb of which the corpus luysi forms a small indentation in which it lies. The corpus luysi is composed of a large number of stellate cells (Golgi type I) with a large round nucleus; the protoplasm contains a large amount of pigment occupying ^x/g-Va of the cells. The cells are surrounded by a rich branching of axonal processes. In the corpus luysi terminate fibers from the corpus striatum-fibrae strio-luysianae, which cross the internal capsule and enter the corpus luysi from its lower surface. In the disease of the corpus striatum this system, as well as the corpus luysi, undergoes degeneration. The connection of the corpus luysi with the cortex is a disputed question; some authors believe that a small amount of fibers from the cortex terminate in the corpus luysi. Both corpus luysi are connected by the Forel commissure (commissura subthalamica posterior). Besides these connections some authors admit a connection of the corpus luysi with the nuclei of Guillaud and Burdah via the medial lemniscus, with the visual system, with the nucleus lenticularis of the opposite side (commissura Meynerti) and with the nucleus ruber. Fibers from the corpus luysi go inward and form descending bundles. The corpus luysi receives blood from the anterior choroidal artery, which proceeds either directly from the internal carotid artery, or from the middle cerebral artery, or from the posterior communicating artery. The corpus luysi is very rich in a network of fine capillaries. On the basis of physiological data and the histological structure of the corpus luysi it is considered a vegetative nucleus; it has an influence on vegetative functions through the medium of sympathetic and parasympathetic fibers. Some centers, such as the cilio-spinal sympathetic center, bladder centers, vascular and sweating centers, are dependent on the corpus luysi. Stimulation of the internal parts of the corpus luysi is accompanied by bilateral dilation of the pupil and palpebral fissure; it is assumed that the center of the pupillary pain reflex is located there as well, since cutting the brain behind the corpus luysi causes it to disappear. Besides ocular phenomena, stimulation of the corpus luysi causes sweating and constriction of the vessels. After damage to the corpus luysi the vascular-motor reaction to various stimuli, including mental ones, is disturbed, on the basis of which it is concluded that the corpus luysi serves as a mediator in the vasomotor manifestations of emotions. Some authors consider that the corpus luysi belongs to the regulatory apparatus acting on the tonic equilibrium centers of the mesencephalon, especially on the physiological variation of the tone of the flexors, preparing this variation for the normal function of this system of muscles, whereas the globus pallidus acts on its permanent tone. Thus, in the sense of movement synergy the corpus luysi is in close connection with the extrapyramidal system and possibly plays a role in instinctive movements. Stimulation of the corpus luysi causes gross and rapid variations in the tone of the flexors, which is the basis of ballism; if the disease of the corpus luysi develops not acutely but slowly, choreic movements are observed. The following syndrome of the corpus luysi has been distinguished by German authors: contralateral hemiballism or chorea, contralateral flaccid hemiparesis and hemitonia, increased drive for movements; absence of pathological reflexes; physiological reflexes are normal. Involuntary movements during sleep disappear. - In general it must be said that the physiological role of the corpus luysi is still quite obscure, which is explained by the insufficiency of experiments partly due to the deep position of the corpus luysi.