The Ventral Intermediate Nucleus of the Thalamus

Unlike the case of DBS for the subthalamic nucleus, targeting in the ventral intermediate thalamus depends on identifying the structure that the neurophysiologist must avoid stimulating, namely, the tactile region of the ventral caudal thalamus. Any stimulation current that spreads to the ventral caudal thalamus may produce intolerable paresthesias and consequently limit DBS’s effectiveness. The narrow length of the ventral intermediate thalamus in the anterior-posterior direction poses a challenge. Excessively shallow trajectories in the sagittal plane risk traversing the short axis, an event that renders postoperative management problematic. If the trajectory pursues too shallow an angle in the coronal plane—as might happen when attempting to avoid the lateral ventricle—DBS may lead to stimulation of the head homuncular region, which by dint of its medial situation leads to increased risk of speech, language, and swallowing difficulties.