three circumscript, myelin-rich regions of the subthalamus known as H fields (from Haubenfelder): 1) field H
1, 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 H
2; 2) field H
2, formed by the lenticular fasciculus and arching over the superior border of the subthalamic nucleus, is composed largely of pallidothalamic fibers; 3) field H
3, or prerubral field, is a large field of intermingling gray and white matter immediately rostral to the red nucleus, uniting fields H
1 and H
2 around the medial margin of the zona incerta; its gray matter forms the prerubral nucleus.
See also:
lenticular loop.