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Medical Definition of H fields
1. Three circumscript, myelin-rich regions of the subthalamus known as H fields (from Haubenfelder); 1) field H1, corresponding to the thalamic fasciculus, a horizontal fibre stratum at the junction of the subthalamus and the overlying thalamus, is composed of pallidothalamic and cerebellothalamic fibres (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 dorsal border of the subthalamic nucleus, is composed largely of pallidothalamic fibres; 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. See: lenticular loop. Synonym: campi foreli, tegmental fields of Forel. (05 Mar 2000)