Effects Caused by Stimulation of the Hypothalamus. In addition to the vegetative and endocrine functions of the hypothalamus, stimulation of or lesions in the hypothalamus often have profound effects on emotional behavior of animals and human beings. Some of the behavioral effects of stimulation are the following:
1. Stimulation in the lateral hypothalamus not only causes thirst and eating, as discussed earlier, but also increases the general level of activity of the animal, sometimes leading to overt rage and fighting, as discussed subsequently.
2. Stimulation in the ventromedial nucleus and sur rounding areas mainly causes effects opposite to those caused by lateral hypothalamic stimulation— that is, a sense of satiety, decreased eating, and tranquility. 3. 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.
4. Sexual drive can be stimulated from several areas of the hypothalamus, especially the most anterior and most posterior portions.
Effects Caused by Hypothalamic Lesions. Lesions in the hypothalamus, in general, cause effects opposite to those caused by stimulation. For instance:
1. Bilateral lesions in the lateral hypothalamus will decrease drinking and eating almost to zero, often leading to lethal starvation. These lesions cause extreme passivity of the animal as well, with loss of most of its overt drives.
2. Bilateral lesions of the ventromedial areas of the hypothalamus cause effects that are mainly oppo site to those caused by lesions of the lateral hypo thalamus: excessive drinking and eating, as well as hyperactivity and often frequent bouts of extreme rage upon the slightest provocation.
Stimulation or lesions in other regions of the limbic system, especially in the amygdala, the septal area, and areas in the mesencephalon, often cause effects similar to those elicited from the hypothalamus. We discuss some of these effects in more detail later.
