Functional Anatomy of the Hypothalamus and Pituitary

The hypothalamus forms only a tiny part of the human brain but nevertheless controls, through feedforward and feedback connections with the pituitary gland, the autonomic nervous system, and other parts of the brain, nearly all the important aspects of our developing and adult life and enables us to respond appropriately to our changing environment. The hypothalamus influences our reproductive systems; the growth of the body, feeding behaviour, metabolic rate, and energy balance; our water and electrolyte balance; and our day–night rhythms. Not surprisingly it has links with the reward systems that influence behavioural and emotional responses including aggressive and affiliative/social behaviour. Whereas some neurons form distinct nuclei, others are more diffusely distributed and few obvious fibre bundles interconnect them. Therefore, although many clinical conditions have long been associated with hypothalamic dysfunction, it is only fairly recently that techniques such as genetic manipulation and optogenetic stimulation have enabled the functions and connections of defined groups of neurons to be unravelled.