Brain stimulation reward (BSR) is a pleasurable phenomenon elicited via direct stimulation of specific brain regions, originally discovered by James Olds and Peter Milner. BSR can serve as a robust operant reinforcer. Targeted stimulation activates the reward system circuitry and establishes response habits similar to those established by natural rewards, such as food and sex. Experiments on BSR soon demonstrated that stimulation of the lateral hypothalamus, along with other regions of the brain associated with natural reward, was both rewarding as well as motivation-inducing. Electrical brain stimulation and intracranial drug injections produce robust reward sensation due to a relatively direct activation of the reward circuitry. This activation is considered to be more direct than rewards produced by natural stimuli, as those signals generally travel through the more indirect peripheral nerves. BSR has been found in all vertebrates tested, including humans, and it has provided a useful tool for understanding how natural rewards are processed by specific brain regions and circuits, as well the neurotransmission associated with the reward system.