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A reward is something that an animal will work to obtain, for example, food. James Olds (1954) was the first to discover that rats will perform arbitrary operant responses to obtain electrical stimulation of some brain regions (e.g. the lateral hypothalamus). The phenomenon is called brain stimulation reward (BSR), and also refers to the reward produced by injections of pharmacological agents (e.g. amphetamine) into the brain.

This behaviour is found in all vertebrates tested (Rolls, 1975) and animals will work to stimulate different neural sites depending on their current state. For example, stimulation at one site is chosen when rats are hungry and at another when rats are thirsty (Gallistel & Beagley, 1971). Thus BSR can act like a specific natural reward, activating the same neurons that are activated in natural circumstances. For example, hunger increases BSR in the lateral hypothalamus and orbitofrontal cortex, and the same neurons are activated by the sight, taste or smell of food if hungry. The implication is that BSR taps into the natural reward system of the brain.

An interesting finding that has resulted from BSR experiments, is that reward, in itself, does not produce satiety (Olds, 1958). BSR experiments have also been helpful in understanding the way that the brain is organised to govern behaviour. BSR is not found in brain areas involved in early sensory processing areas (e.g. visual areas up to and including the inferior temporal cortex), so it can be deduced that reward is only represented at certain stages of the pathways that lead from sensory input to motor output (e.g. orbitofrontal cortex).

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