Animals, and particularly rodents that are routinely used in observations and experiments, tell us a lot of what we know about our own psychology. Rodents? How can a mouse or a rat know the first thing about what motivates and directs human reactions and behaviors? As a matter of fact, no rodent has yet provided any evidence of self-awareness or consciousness of the elevated kind, the sense of self that we attribute to ourselves and that is often used to explain why we do the things we do. And that is the very reason why rodents make such reliable exemplars of human psychology.
An animal is not burdened by the double edge sword of reason, and is content to function with the rather blunt instrument of instinct. In animals, some of the behavioral effects of plain and simple mechanical stimulation (either via contact or a mild electrical current) are immediate and evident. The animal does absolutely nothing to control its reactions or responses. Touch this, it does that. Touch that, it does this. Plain. Simple. Predictable. Why is this important? It is thanks to this unfiltered animal response that we are able to pinpoint the function of brain structures that are identical and present in both animals and humans.
Some specific examples can better illustrate this point. Stimulation in the lateral hypothalamus not only causes thirst and hunger, but also increases the general level of activity of the animal (of the human as well), sometimes leading to overt rage and ﬁghting.
Stimulation in the ventromedial nucleus and surrounding areas mainly causes effects opposite to those caused by lateral hypothalamic stimulation—that is, a sense of satiety, decreased eating, and tranquility. Stimulation of a thin zone of periventricular nuclei, located immediately adjacent to the third ventricle (or also stimulation of the central gray area of the mesencephalon that is continuous with this portion of the hypothalamus), usually leads to fear and punishment reactions.
Sexual drive can be stimulated from several areas of the hypothalamus, especially the most anterior and most posterior portions of the hypothalamus.
As one of the oldest structures of the brain, the hypothalamus area is the center of activity for the most primordial functions of the rodent and as it turns out, of the human: thirst, hunger, aggressiveness and sex, all necessary to basic survival and reproduction. Studying the rodent does not tell us why, but it tells us exactly where and how these emotions are located and how they can be inhibited or disinhibited by precise stimulation.