three circumscript, myelin-rich regions of the subthalamus known as H fields (from Haubenfelder): 1) field H1, corresponding to the thalamic fasciculus, a fiber stratum at the junction of the zona incerta and the overlying thalamus, is composed of pallidothalamic and cerebellothalamic fibers (brachium conjunctivum) and is separated by the zona incerta from the more ventrally placed field H2; 2) field H2, formed by the lenticular fasciculus and arching over the superior border of the subthalamic nucleus, is composed largely of pallidothalamic fibers; 3) field H3, or prerubral field, is a large field of intermingling gray and white matter immediately rostral to the red nucleus, uniting fields H1 and H2 around the medial margin of the zona incerta; its gray matter forms the prerubral nucleus.lenticular loop. SYN: campi foreli, tegmental fields of Forel.