Brain stimulation reward

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. Intracranial self-stimulation (ICSS) is the operant conditioning method used to produce BSR in an experimental setting. ICSS typically involves subjects with permanent electrode implants in one of several regions of the brain known to produce BSR when stimulated. Subjects are trained to continuously respond to electrical stimulation of that brain region. ICSS studies have been particularly useful for examining the effects of various pharmacological manipulations on reward sensitivity. ICSS has been utilized as a means to gauge addiction liability for drugs of many classes, including those that act on monoaminergic, opioid, and cholinergic neurotransmission. These data correlate well with findings from self-administration studies on the addictive properties of drugs.