Incentive salience

Addiction and dependence glossary[1][2][3][4]
• addiction – a medical condition characterized by compulsive engagement in rewarding stimuli despite adverse consequences
• addictive behavior – a behavior that is both rewarding and reinforcing
• addictive drug – a drug that is both rewarding and reinforcing
• 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 or as something to be approached
• 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

Incentive salience is a desire or want attribute, which includes a motivational component, that is assigned by the brain – specifically, by the nucleus accumbens shell – to a rewarding stimulus.^[5][6][7] Reward is the attractive and motivational property of a stimulus that induces appetitive behavior – also known as approach behavior – and consummatory behavior.^[7] The "wanting" of incentive salience differs from "liking" in the sense that liking is the pleasure that is immediately gained from the acquisition or consumption of a rewarding stimulus;^[5][8] the "wanting" of incentive salience serves a "motivational magnet" quality of a rewarding stimulus that makes it a desirable and attractive goal, transforming it from a mere sensory experience into something that commands attention, induces approach, and causes it to be sought out.^[5][8] Incentive salience is primarily regulated by dopamine neurotransmission in the mesocorticolimbic projection,^[5][6][8][9] but activity in other dopaminergic pathways and hedonic hotspots (e.g., the ventral pallidum) also modulate incentive salience.^[6][8]

Incentive salience is the form of motivational salience that is associated with reward (an attractive phenomenon), as opposed to punishment (an avoidance phenomenon).^[6][7]

Clinical significance

The assignment of incentive salience to stimuli is dysregulated in addiction. During the development of an addiction, the repeated association of otherwise neutral and even non-rewarding stimuli with drug consumption triggers an associative learning process that causes these previously neutral stimuli to become secondary reinforcers of addictive drug use. As secondary reinforcers of drug use, these previously neutral stimuli are assigned incentive salience (which manifests as a craving), sometimes at pathologically high levels, which transfers to the primary reinforcer (i.e., the use of an addictive drug) with which it was originally paired. Thus, if a person's addiction subsides and the individual subsequently encounters one of these secondary reinforcers, a craving for that drug may reappear. For example, anti-drug agencies previously used posters with images of drug paraphernalia as an attempt to show the dangers of drug use. However, such posters are no longer used because of the effects of incentive salience in causing relapse upon sight of the stimuli illustrated in the posters.

In addiction, the "liking" (pleasure or hedonic value) of a drug or other stimulus becomes dissociated from the "wanting" (level of desire for) attribute due to the sensitization of incentive salience.^[10] In fact, if the incentive salience associated with drug-taking becomes pathologically amplified, the user may want the drug more and more while liking it less and less as tolerance develops to the drug's pleasurable effects.

See also

• Dopamine
• Kent C. Berridge
• Pleasure
• Reward system

References

1. Malenka RC, Nestler EJ, Hyman SE (2009). "Chapter 15: Reinforcement and Addictive Disorders". In Sydor A, Brown RY. Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. pp. 364–375. ISBN 9780071481274.
2. Nestler EJ (December 2013). "Cellular basis of memory for addiction". Dialogues Clin. Neurosci. 15 (4): 431–443. PMC 3898681. PMID 24459410.
3. "Glossary of Terms". Mount Sinai School of Medicine. Department of Neuroscience. Retrieved 9 February 2015.
4. Volkow ND, Koob GF, McLellan AT (January 2016). "Neurobiologic Advances from the Brain Disease Model of Addiction". N. Engl. J. Med. 374 (4): 363–371. doi:10.1056/NEJMra1511480. PMID 26816013.
5. Berridge KC (April 2012). "From prediction error to incentive salience: mesolimbic computation of reward motivation". Eur. J. Neurosci. 35 (7): 1124–1143. doi:10.1111/j.1460-9568.2012.07990.x. PMC 3325516. PMID 22487042. Here I discuss how mesocorticolimbic mechanisms generate the motivation component of incentive salience. Incentive salience takes Pavlovian learning and memory as one input and as an equally important input takes neurobiological state factors (e.g. drug states, appetite states, satiety states) that can vary independently of learning. Neurobiological state changes can produce unlearned fluctuations or even reversals in the ability of a previously learned reward cue to trigger motivation. Such fluctuations in cue-triggered motivation can dramatically depart from all previously learned values about the associated reward outcome. ... Associative learning and prediction are important contributors to motivation for rewards. Learning gives incentive value to arbitrary cues such as a Pavlovian conditioned stimulus (CS) that is associated with a reward (unconditioned stimulus or UCS). Learned cues for reward are often potent triggers of desires. For example, learned cues can trigger normal appetites in everyone, and can sometimes trigger compulsive urges and relapse in addicts.
   Cue-triggered ‘wanting’ for the UCS
   A brief CS encounter (or brief UCS encounter) often primes a pulse of elevated motivation to obtain and consume more reward UCS. This is a signature feature of incentive salience.
   Cue as attractive motivational magnets
   When a Pavlovian CS+ is attributed with incentive salience it not only triggers ‘wanting’ for its UCS, but often the cue itself becomes highly attractive – even to an irrational degree. This cue attraction is another signature feature of incentive salience ... Two recognizable features of incentive salience are often visible that can be used in neuroscience experiments: (i) UCS-directed ‘wanting’ – CS-triggered pulses of intensified ‘wanting’ for the UCS reward; and (ii) CS-directed ‘wanting’ – motivated attraction to the Pavlovian cue, which makes the arbitrary CS stimulus into a motivational magnet.
6. Malenka RC, Nestler EJ, Hyman SE (2009). Sydor A, Brown RY, eds. Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. pp. 147–148, 367, 376. ISBN 978-0-07-148127-4. VTA DA neurons play a critical role in motivation, reward-related behavior (Chapter 15), attention, and multiple forms of memory. This organization of the DA system, wide projection from a limited number of cell bodies, permits coordinated responses to potent new rewards. Thus, acting in diverse terminal fields, dopamine confers motivational salience (“wanting”) on the reward itself or associated cues (nucleus accumbens shell region), updates the value placed on different goals in light of this new experience (orbital prefrontal cortex), helps consolidate multiple forms of memory (amygdala and hippocampus), and encodes new motor programs that will facilitate obtaining this reward in the future (nucleus accumbens core region and dorsal striatum). In this example, dopamine modulates the processing of sensorimotor information in diverse neural circuits to maximize the ability of the organism to obtain future rewards. ...
   The brain reward circuitry that is targeted by addictive drugs normally mediates the pleasure and strengthening of behaviors associated with natural reinforcers, such as food, water, and sexual contact. Dopamine neurons in the VTA are activated by food and water, and dopamine release in the NAc is stimulated by the presence of natural reinforcers, such as food, water, or a sexual partner. ...
   The NAc and VTA are central components of the circuitry underlying reward and memory of reward. As previously mentioned, the activity of dopaminergic neurons in the VTA appears to be linked to reward prediction. The NAc is involved in learning associated with reinforcement and the modulation of motoric responses to stimuli that satisfy internal homeostatic needs. The shell of the NAc appears to be particularly important to initial drug actions within reward circuitry; addictive drugs appear to have a greater effect on dopamine release in the shell than in the core of the NAc.
7. Schultz W (2015). "Neuronal reward and decision signals: from theories to data" (PDF). Physiological Reviews. 95 (3): 853–951. doi:10.1152/physrev.00023.2014. Archived from the original (PDF) on 6 September 2015. Retrieved 24 September 2015. 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, 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 (FIGURE 1, middle). 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 (FIGURE 1, right). 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. ... These emotions are also called liking (for pleasure) and wanting (for desire) in addiction research (471) and strongly support the learning and approach generating functions of reward.
8. Berridge KC, Kringelbach ML (May 2015). "Pleasure systems in the brain". Neuron. 86 (3): 646–664. doi:10.1016/j.neuron.2015.02.018. PMC 4425246. PMID 25950633. In the prefrontal cortex, recent evidence indicates that the OFC and insula cortex may each contain their own additional hot spots (D.C. Castro et al., Soc. Neurosci., abstract). In specific subregions of each area, either opioid-stimulating or orexin-stimulating microinjections appear to enhance the number of ‘‘liking’’ reactions elicited by sweetness, similar to the NAc and VP hot spots. Successful confirmation of hedonic hot spots in the OFC or insula would be important and possibly relevant to the orbitofrontal mid-anterior site mentioned earlier that especially tracks the subjective pleasure of foods in humans (Georgiadis et al., 2012; Kringelbach, 2005; Kringelbach et al., 2003; Small et al., 2001; Veldhuizen et al., 2010). Finally, in the brainstem, a hindbrain site near the parabrachial nucleus of dorsal pons also appears able to contribute to hedonic gains of function (Söderpalm and Berridge, 2000). A brainstem mechanism for pleasure may seem more surprising than forebrain hot spots to anyone who views the brainstem as merely reflexive, but the pontine parabrachial nucleus contributes to taste, pain, and many visceral sensations from the body and has also been suggested to play an important role in motivation (Wu et al., 2012) and in human emotion (especially related to the somatic marker hypothesis) (Damasio, 2010). ... In Pavlovian reward situations, some cues for reward become ‘‘wanted’’ more than others as powerful motivational magnets, in ways that differ across individuals (Robinson et al., 2014b; Saunders and Robinson, 2013).
9. Berridge, Kent C.; O’Doherty, John P. (2014-01-01). Fehr, Paul W. GlimcherErnst, ed. Chapter 18 - From Experienced Utility to Decision Utility. San Diego: Academic Press. pp. 335–351. ISBN 978-0-12-416008-8.
10. Berridge, K.C., Robinson, T.E. What is the role of dopamine in reward: hedonic impact, reward learning, or incentive salience? Brain Res Brain Res Rev. 1998 Dec; 28(3):309–69.