The human hypothalamus: a morpho-functional perspective

Historical investigation suggests that the role of the hypothalamus as a site of integration for endocrine with autonomic and behavioral responses in man rises from ideas and observations first appearing between the 14th and 18th centuries. Research on human, post-mortem brains and by in vivo magnetic resonance techniques reveal that the functional morphology of the hypothalamus in man is very similar to that in Rodents and Primates. As such, the adult human hypothalamus can be subdivided in three longitudinal zones, representing the source and target of neural informations traveling back and forth the brain stem, thalamus, limbic system, basal ganglia and neocortex. In addition, the human hypothalamus can be further partitioned in three anterior-posterior regions, of which the rostral one exerts a prominent regulation in predictive homeostasis, as opposed to the two caudal ones, primarily involved in reactive homeostasis. Finally, nuclear distribution in the human hypothalamus largely coincides with that in higher Mammals. Nevertheless, it is still unclear how the hypothalamus may give rise to specific homeostatic behaviors like hunger, thirst, reproductive and parental attitude, thermoregulation, aggressive-defensive performance, affective-motivational tone, circadian rhythmicity, sleep-wake cycle and immune regulation. The recent advent of new theories for nervous communication, like volume transmission and neural Darwinism, is progressively enlightening our understanding of the role played by the hypothalamic architecture in homeostatic responses, both in Mammals and man.