Since the whole organism takes part in an emotion of excitement, a general energizing center for emotions is present. This area is the hypothalamus. The feeling of emotion and the directed behavior which the organism displays to change the environment and bring about a re-establishment of homeostasis are functions of the cerebral cortex.
An emotion-producing situaction initiates neural impulses which pass into the lower structures of the thalamus, or the hypothalamus. From the hypothalamus these impulses go to the muscles and glands producing the physiological effects of the emotion. At the same time the impulses from the hypothalamus go to the cerebral cortex, producing the feeling of an emotion. The responses of the effectors produce their own stimuli, the impulses of which go to the thalamus, reinforcing the emotional response. These impulses also go to the cerebral cortex. Thus the experience of the emotions results from the impulses which reach the cortex from the direct stimulation which initiates the emotional behavior and from the impulses created by the effectors which are thrown into activity. The cerebral cortex integrates these impulses, and behavior appropriate to the situation is the result. Another function of the cortex is its inhibitory effect on the hypothalamus. The cortex acts to decrease the emotional responses which would result from the hypothalamic center if no cortical connections were present.
A strong emotional response to intense stimuli may be inhibited, but the impulses from the thalamic center reach the muscles and the glands a short time before the cortical impulses act to modify the response, so that a startle reaction will be given approximately 1/10 of a second following a loud noise or any other intense and unexpected stimulus. The startle pattern may not be perceptible to common observation because the cortex may inhibit it very soon after it starts. High speed photography has shown that the pattern, or part of it, is present to a greater or lesser extent in all normal individuals. Thus the individual reacts to threatening situations before he can inhibit the movement.