- Brain stimulation reward
James Oldswas the first to discover that rats will perform arbitrary operant responses to obtain electrical stimulation of some brain regions (e.g. the lateral hypothalamus).Olds J, Milner P. "Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain." "Journal of Comparative and Physiological Psychology." 1954 Dec; 47(6):419-27. PMID 13233369] The phenomenon is called brain stimulation reward (BSR), and also refers to the reward produced by injections of certain recreational drugs(e.g. amphetamineor morphine) directly into the brain.
This behaviour is found in all
vertebrates testedRolls ET. "The neural basis of brain-stimulation reward." "Progress in Neurobiology." 1975; 3:73-160. PMID 1162082] 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 CR, Beagley G. "Specificity of brain stimulation reward in the rat." "Journal of Comparative and Physiological Psychology." 1971 Aug; 76(2):199-205. PMID 5159006] Thus BSR can act like a specific natural reward, activating the same neuronsthat are activated in natural circumstances. For example, hunger increases BSR in the lateral hypothalamusand orbitofrontal cortex, and the same neuronsare activated by the sight, taste or smell of food when the organism is hungry. The implication is that BSR taps into the natural reward systemof the brain.Wise RA. "Brain reward circuitry: insights from unsensed incentives." "Neuron". 2002 Oct 10; 36(2):229-40. PMID 12383779]
An interesting finding that has resulted from BSR experiments, is that reward, in itself, does not produce satiety.Olds J. "Satiation effects in self-stimulation of the brain." "Journal of Comparative and Physiological Psychology." 1958 Dec; 51(6):675-8. PMID 13620802] BSR experiments have also been helpful in understanding the way that the brain is organised to govern behavior, especially with regard to
addictive behavior. 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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