The tiny hypothalamus serves as the Health Maintenance Organization of
the body, regulating its homeostasis, or stable state of equilibrium.
The hypothalamus also generates behaviors involved in eating,
drinking, general arousal, rage, aggression, embarrassment, escape
from danger, pleasure and copulation. It does an amazing number of
housekeeping chores for such a small piece of tissue. Its lateral and
anterior parts seem to support activation of the parasympathetic
nervous system: drop in blood pressure; slowing of pulse; and
regulation of digestion, defecation, assimilation, and reproduction in
such a way as to contribute on the whole to rest and recovery. The
medial and posterior hypothalamus regulate activation: acceleration of
pulse and breathing rates, high blood pressure, arousal, fear and
anger. Stimulation of specific groups of cells in these areas can
elicit pure behaviors. For example, rats placed in an experimental
situation where they can press a lever to stimulate a pleasure center
will do so to the exclusion of eating and drinking.
