Scientists may also use stimulation to discover the role of a structure in species-typical behavior. In a 1957 experiment, physiologist Walter Hess used an electrode to stimulate a certain part of a resting cat's brainstem; immediately after the stimulation, the cat stood up and arched its back with erect hair—a species-typical behavior in which cats engage when frightened. The behavior lasted as long as the stimulation lasted, and ended as soon as the stimulation ended. Later experiments revealed that even if the same part of the brain is stimulated with the same amount of energy for the same period of time, the intensity of the elicited behavior changes depending on the context. In 1973, behavioral physiologist Erich von Holst attached an electrode to one part of a chicken's brainstem. When briefly stimulated without any unusual environmental factors, the chicken was restless. When briefly stimulated in the presence of a human fist, the chicken reacted with a slightly threatening posture, and in the presence of a weasel, the chicken took a very threatening pose, with feathers bristling. The brainstem, in this case, elicits species-typical behavior that is appropriate to the surrounding environment.
