[TA] a flat, obliquely disposed plate of gray matter in the subthalamic region situated between the thalamic fasciculus (tegmental field H1 of Forel) and the lenticular fasciculus (tegmental field H2). Medially, cells of this nucleus are adjacent to the prerubral area (tegmental field H) and, laterally, they are continuous with the reticular nucleus of the thalamus. Z. i. is a derivative of the ventral thalamus; it receives afferents from the precentral motor cortex and the cerebellum.