Reward system

The reward system (the mesocorticolimbic circuit) is a group of neural structures responsible for incentive salience (i.e., "wanting"; desire or craving for a reward and motivation), associative learning (primarily positive reinforcement and classical conditioning), and positively-valenced emotions, particularly ones involving pleasure as a core component (e.g., joy, euphoria and ecstasy).[1][2] Reward is the attractive and motivational property of a stimulus that induces appetitive behavior, also known as approach behavior, and consummatory behavior.[1] A rewarding stimulus has been described as "any stimulus, object, event, activity, or situation that has the potential to make us approach and consume it is by definition a reward".[1] In operant conditioning, rewarding stimuli function as positive reinforcers;[3] however, the converse statement also holds true: positive reinforcers are rewarding.[3][4]

Examples of primary rewards.[3] Clockwise from top left: water, food, parental care, and sex.
Addiction and dependence glossary[5][6][7][8]
  • addiction – a biopsychosocial disorder characterized by persistent use of drugs (including alcohol) despite substantial harm and adverse consequences
  • addictive drug – psychoactive substances that with repeated use are associated with significantly higher rates of substance use disorders, due in large part to the drug's effect on brain reward systems
  • dependence – an adaptive state associated with a withdrawal syndrome upon cessation of repeated exposure to a stimulus (e.g., drug intake)
  • drug sensitization or reverse tolerance – the escalating effect of a drug resulting from repeated administration at a given dose
  • drug withdrawal – symptoms that occur upon cessation of repeated drug use
  • physical dependence – dependence that involves persistent physical–somatic withdrawal symptoms (e.g., fatigue and delirium tremens)
  • psychological dependence – dependence that involves emotional–motivational withdrawal symptoms (e.g., dysphoria and anhedonia)
  • reinforcing stimuli – stimuli that increase the probability of repeating behaviors paired with them
  • rewarding stimuli – stimuli that the brain interprets as intrinsically positive and desirable or as something to approach
  • sensitization – an amplified response to a stimulus resulting from repeated exposure to it
  • substance use disorder – a condition in which the use of substances leads to clinically and functionally significant impairment or distress
  • tolerance – the diminishing effect of a drug resulting from repeated administration at a given dose

The reward system motivates animals to approach stimuli or engage in behaviour that increases fitness (sex, energy-dense foods, etc.). Survival for most animal species depends upon maximizing contact with beneficial stimuli and minimizing contact with harmful stimuli. Reward cognition serves to increase the likelihood of survival and reproduction by causing associative learning, eliciting approach and consummatory behavior, and triggering positively-valenced emotions.[3] Thus, reward is a mechanism that evolved to help increase the adaptive fitness of animals.[9] In drug addiction, certain substances over-activate the reward circuit, leading to compulsive substance-seeking behavior resulting from synaptic plasticity in the circuit.[10]

Primary rewards are a class of rewarding stimuli which facilitate the survival of one's self and offspring, and they include homeostatic (e.g., palatable food) and reproductive (e.g., sexual contact and parental investment) rewards.[1][11] Intrinsic rewards are unconditioned rewards that are attractive and motivate behavior because they are inherently pleasurable.[1] Extrinsic rewards (e.g., money or seeing one's favorite sports team winning a game) are conditioned rewards that are attractive and motivate behavior but are not inherently pleasurable.[1][12] Extrinsic rewards derive their motivational value as a result of a learned association (i.e., conditioning) with intrinsic rewards.[1] Extrinsic rewards may also elicit pleasure (e.g., euphoria from winning a lot of money in a lottery) after being classically conditioned with intrinsic rewards.[1]

  1. ^ a b c d e f g h Cite error: The named reference pmid26109341 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference Pleasure system was invoked but never defined (see the help page).
  3. ^ a b c d Schultz W (2015). "Neuronal reward and decision signals: from theories to data". Physiological Reviews. 95 (3): 853–951. doi:10.1152/physrev.00023.2014. PMC 4491543. PMID 26109341. Rewards in operant conditioning are positive reinforcers. ... Operant behavior gives a good definition for rewards. Anything that makes an individual come back for more is a positive reinforcer and therefore a reward. Although it provides a good definition, positive reinforcement is only one of several reward functions. ... Rewards are attractive. They are motivating and make us exert an effort. ... Rewards induce approach behavior, also called appetitive or preparatory behavior, sexual behavior, and consummatory behavior. ... Thus any stimulus, object, event, activity, or situation that has the potential to make us approach and consume it is by definition a reward. ... Rewarding stimuli, objects, events, situations, and activities consist of several major components. First, rewards have basic sensory components (visual, auditory, somatosensory, gustatory, and olfactory) ... Second, rewards are salient and thus elicit attention, which are manifested as orienting responses. The salience of rewards derives from three principal factors, namely, their physical intensity and impact (physical salience), their novelty and surprise (novelty/surprise salience), and their general motivational impact shared with punishers (motivational salience). A separate form not included in this scheme, incentive salience, primarily addresses dopamine function in addiction and refers only to approach behavior (as opposed to learning) ... Third, rewards have a value component that determines the positively motivating effects of rewards and is not contained in, nor explained by, the sensory and attentional components. This component reflects behavioral preferences and thus is subjective and only partially determined by physical parameters. Only this component constitutes what we understand as a reward. It mediates the specific behavioral reinforcing, approach generating, and emotional effects of rewards that are crucial for the organism's survival and reproduction, whereas all other components are only supportive of these functions. ... Rewards can also be intrinsic to behavior. They contrast with extrinsic rewards that provide motivation for behavior and constitute the essence of operant behavior in laboratory tests. Intrinsic rewards are activities that are pleasurable on their own and are undertaken for their own sake, without being the means for getting extrinsic rewards. ... Intrinsic rewards are genuine rewards in their own right, as they induce learning, approach, and pleasure, like perfectioning, playing, and enjoying the piano. Although they can serve to condition higher order rewards, they are not conditioned, higher order rewards, as attaining their reward properties does not require pairing with an unconditioned reward. ... These emotions are also called liking (for pleasure) and wanting (for desire) in addiction research and strongly support the learning and approach generating functions of reward.
  4. ^ Guo, Rong; Böhmer, Wendelin; Hebart, Martin; Chien, Samson; Sommer, Tobias; Obermayer, Klaus; Gläscher, Jan (14 December 2016). "Interaction of Instrumental and Goal-Directed Learning Modulates Prediction Error Representations in the Ventral Striatum". The Journal of Neuroscience. Society for Neuroscience. 36 (50): 12650–12660. doi:10.1523/jneurosci.1677-16.2016. ISSN 0270-6474. PMC 6705659. PMID 27974615.
  5. ^ Malenka RC, Nestler EJ, Hyman SE (2009). "Chapter 15: Reinforcement and Addictive Disorders". In Sydor A, Brown RY (eds.). Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. pp. 364–375. ISBN 9780071481274.
  6. ^ Nestler EJ (December 2013). "Cellular basis of memory for addiction". Dialogues in Clinical Neuroscience. 15 (4): 431–443. PMC 3898681. PMID 24459410. Despite the importance of numerous psychosocial factors, at its core, drug addiction involves a biological process: the ability of repeated exposure to a drug of abuse to induce changes in a vulnerable brain that drive the compulsive seeking and taking of drugs, and loss of control over drug use, that define a state of addiction. ... A large body of literature has demonstrated that such ΔFosB induction in D1-type [nucleus accumbens] neurons increases an animal's sensitivity to drug as well as natural rewards and promotes drug self-administration, presumably through a process of positive reinforcement ... Another ΔFosB target is cFos: as ΔFosB accumulates with repeated drug exposure it represses c-Fos and contributes to the molecular switch whereby ΔFosB is selectively induced in the chronic drug-treated state.41. ... Moreover, there is increasing evidence that, despite a range of genetic risks for addiction across the population, exposure to sufficiently high doses of a drug for long periods of time can transform someone who has relatively lower genetic loading into an addict.
  7. ^ "Glossary of Terms". Mount Sinai School of Medicine. Department of Neuroscience. Retrieved 9 February 2015.
  8. ^ Volkow ND, Koob GF, McLellan AT (January 2016). "Neurobiologic Advances from the Brain Disease Model of Addiction". New England Journal of Medicine. 374 (4): 363–371. doi:10.1056/NEJMra1511480. PMC 6135257. PMID 26816013. Substance-use disorder: A diagnostic term in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) referring to recurrent use of alcohol or other drugs that causes clinically and functionally significant impairment, such as health problems, disability, and failure to meet major responsibilities at work, school, or home. Depending on the level of severity, this disorder is classified as mild, moderate, or severe.
    Addiction: A term used to indicate the most severe, chronic stage of substance-use disorder, in which there is a substantial loss of self-control, as indicated by compulsive drug taking despite the desire to stop taking the drug. In the DSM-5, the term addiction is synonymous with the classification of severe substance-use disorder.
  9. ^ Cite error: The named reference Behavioral neuroscience textbook was invoked but never defined (see the help page).
  10. ^ Brain & Behavior Research Foundation (13 March 2019). "The Biology of Addiction". YouTube.{{cite web}}: CS1 maint: url-status (link)
  11. ^ "Dopamine Involved In Aggression". Medical News Today. 15 January 2008. Archived from the original on 23 September 2010. Retrieved 14 November 2010.
  12. ^ Duarte, Isabel C.; Afonso, Sónia; Jorge, Helena; Cayolla, Ricardo; Ferreira, Carlos; Castelo-Branco, Miguel (1 May 2017). "Tribal love: the neural correlates of passionate engagement in football fans". Social Cognitive and Affective Neuroscience. 12 (5): 718–728. doi:10.1093/scan/nsx003. PMC 5460049. PMID 28338882.

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