One of three subzones of the hypothalamus, the others of which include the periventricular and lateral zones. It includes the paraventricular, supraoptic, medial preoptic nuclei; anterior, ventromedial, and dorsomedial nuclei of the hypothalamus; retrochiasmatic area, supramammillary nucleus, medial part of the medial mammillary nucleus, and lateral mammillary nucleus.