Figure 6.3: Lever pressing for electrical stimulation to the brain Each time this rat presses the lever, it receives a brief pulse of electrical current through an electrode implanted in its brain. Some of Olds’s rats continued to press the lever for 24 hours without rest, as often as 5,000 times per hour (Olds, 1956).
Olds, J. (1956, October). Pleasure centers in the brain. Scientific American, 112.