SEPTAL AREA (Septal Region, Septum)

A region of the brain lying beneath the forward end of the corpus callosum, the connection between the two hemispheres. It is part of the limbic system.Experiments have shown that when lesions are made in the septal area, or in fibers running from this region to the hypothalamus, rats and other animals overreact emotionally. They become ferocious and dangerous to handle, and will attack any object thrust at them. In addition, they become more jumpy, easily startled, and will resist capture and handling (Brady and Nauta, 1953; King, 1958). The intensity of these reactions tends to subside in time (Reynolds, 1963), probably because the lesions were not complete enough to destroy the entire function. When conditioning experiments were performed on septal animals, it was found that they learned active avoidance responses more quickly than normal animals—that is, they learned to avoid a shock by shuttling from a shock compartment to a nonshock compartment in an experimental enclosure. This follows from the fact that the destruction of the area made them more emotional.These results indicate that the intact septum exerts a restraining influence on the hypothalamus. Further experiments in which the septum and the amygdala were removed one after the other showed that the two areas work in opposition to each other, the amygdala exerting an excitatory and the septum an inhibitory effect.