A group of widely spaced, medium-size neurons in the dorsomedial region of the upper mesencephalic tegmentum, immediately lateral to the [[nucleus of Darkschewitsch]]; together with the latter, the interstitial nucleus is closely associated with the [[medial longitudinal fasciculus]], through which it receives fibers from the vestibular nuclei and projects crossed fibers through the posterior commissure to the oculomotor nucleus; also projects fibers to all spinal levels. It is believed to be involved in the integration of head and eye movements, particularly eye movements of a vertical or oblique nature.