Brain. 1. A subcortical group of nuclei in the forebrain which serves a. the limbic system, b. the autonomic nervous system (see FIGHT-OR-FLIGHT), and c. the endocrine system. 2. A thumbnail-sized neuro structure which organizes basic nonverbal responses, such asaggression, anger, sexuality, and fear.
Usage: Giving input to--and receiving output from--the limbic system, the hypothalamus mediates diverse nonverbal signs associated withemotion and psychological arousal.
Evolution I. The hypothalamus has deep evolutionary roots in the chemical sense of smell (see AROMA CUE).
Evolution II. As the forebrain's main chemical-control area, the hypothalamus regulates piscine adrenal medullae, chemical-releasing glands which, in living fish, consist of two lines of cells near the kidneys. The adrenal medullae pump adrenaline into the bloodstream, from where it effects every cell in the fish's body. (N.B.: In humans, adrenaline speeds up body movements, strengthens muscle contractions, and energizesthe activity of spinal-cord paleocircuits.)
RESEARCH REPORTS: 1. Pathways involved in oral and genital functions "converge in that part of the hypothalamus in which electrical stimulation results in angry and defensive behaviour" (MacLean 1973:44). 2. In higher vertebrates, the olfactory system and the hypophysis [i.e., the pituitary gland (which is linked to the hypothalamus)] "are derived from a single patch of embryonic [neuro]ectoderm" (Stoddart 1990:13). 3. The hypothalamus mediates many nonverbal behaviors through reticular nuclei in the brain stem (Guyton 1996).
Neuro-notes. Regarding hypothalamic nuclei and nonverbal signs, a. the dorsomedial nucleus stimulates savage behavior; b. the posterior nucleus stimulates the sympathetic nervous system; c. the preoptic area houses the sexual dimorphic nucleus; and d. the anterior nucleus stimulates the parasympathetic nervous system (Fix 1995; see REST-AND-DIGEST).
Detail of illustration from Mapping the Mind (p. 70; copyright Weidenfeld & Nicolson, London, 1998 [the medial preoptic area governs male sex drive])