Pavlovian-instrumental transfer (PIT) is a psychological phenomenon that occurs when a conditioned stimulus (CS, also known as a "cue") that has been associated with rewarding or aversivestimuli via classical conditioning alters motivational salience and operant behavior.[1][2][3][4] Two distinct forms of Pavlovian-instrumental transfer have been identified in humans and other animals – specific PIT and general PIT – with unique neural substrates mediating each type.[1][5][6] In relation to rewarding stimuli, specific PIT occurs when a CS is associated with a specific rewarding stimulus through classical conditioning and subsequent exposure to the CS enhances an operant response that is directed toward the same reward with which it was paired (i.e., it promotes approach behavior).[1][5][6] General PIT occurs when a CS is paired with one reward and it enhances an operant response that is directed toward a different rewarding stimulus.[1][5][6]
An example of specific PIT, as described by a neuroscience review on Pavlovian-instrumental transfer from 2013,[1] is as follows:
In a typical experimental scenario a rat is trained to associate a sound (CS) with the delivery of food. Later, the rat undergoes an instrumental training where it learns to press a lever to get some food (without the sound being present). Finally, the rat is presented again with the opportunity to press the lever, this time both in the presence and absence of the sound. The results show that the rat will press the lever more in the presence of the sound than without, even if the sound has not been previously paired with lever pressing. The Pavlovian sound-food association learned in the first phase has somehow transferred to the instrumental situation, hence the name 'Pavlovian-instrumental transfer'.[1]
Specific and general transfer
In relation to rewarding stimuli, specific PIT occurs when a CS is associated with a specific rewarding stimulus through classical conditioning and subsequent exposure to the CS enhances an operant response that is directed toward the same reward with which it was paired (i.e., it promotes approach behavior).[1][5][6] General PIT occurs when a CS is paired with one reward and it enhances an operant response that is directed toward a different rewarding stimulus.[1][5][6] Neurobiological state factors (e.g., appetite and satiety states, stress level, drug states such as intoxication and withdrawal, etc.), and particularly the motivational state of an animal, strongly affect the amount of appetitive motivational salience (i.e., incentive salience) that a reward cue[note 1] confers to an associated rewarding stimulus via Pavlovian-instrumental transfer.[1][4][5] Acute stress amplifies the motivational salience that reward cues confer to rewarding stimuli through both specific and general PIT;[5] however, chronic stress reduces the motivational impact reward cues.[5]
Specific PIT and general PIT also occur with aversive stimuli and are defined analogously.[2][5] Specific PIT with an aversive stimulus occurs when a CS is paired with an aversive stimulus and subsequent exposure to the CS enhances an operant response that is directed away from the aversive stimulus with which it was paired (i.e., it promotes escape and avoidance behavior).[2][5] General PIT with an aversive stimulus occurs when a CS is paired with one aversive stimulus and it enhances an operant response that is directed away from a different aversive stimulus.[2][5]
Neural substrates
Based on studies of rats that involved PIT with rewards, it has been found that specific PIT is mediated by the nucleus accumbens shell and basolateral amygdala, while general PIT is mediated by the nucleus accumbens core and central amygdala.[1][6] Studies on humans, which employed neuroimaging during PIT experiments with rewards, appear to be consistent with these findings.[1]
Clinical significance
Addiction
Due to the effect of reward cues and Pavlovian-instrumental transfer on the amplification of incentive salience for rewarding stimuli, PIT is believed to be one of the mechanisms responsible for producing "cue-triggered wanting", or craving, for a drug that occurs when an individual with a drug addiction is exposed to drug cues[note 2] even after long periods of abstinence.[4][5][7] For example, anti-drug agencies previously used posters with images of drug paraphernalia – which is a type of drug cue – as an attempt to show the dangers of drug use. However, such posters are no longer used because of the effect of incentive salience in causing cravings and relapse upon sight of the stimuli illustrated in the posters.
Dieting
The sight or smell of food which one has consumed and enjoyed in the past can elicit hunger (i.e., the motivation to eat) in humans, an effect which is presumably mediated through PIT.[3][4][6] In PIT experiments with rats, the presentation of a conditioned stimulus which has been paired with food has been shown to increase instrumental actions that have been reinforced by food, such as pressing a lever which leads to the delivery of a food pellet.[6]
^ abCartoni E, Balleine B, Baldassarre G (2016). "Appetitive Pavlovian-instrumental Transfer: A review"(PDF). Neuroscience and Biobehavioral Reviews. 71: 829–848. doi:10.1016/j.neubiorev.2016.09.020. PMID27693227. This paper reviews one of the experimental paradigms used to study the effects of cues, the Pavlovian to Instrumental Transfer paradigm. In this paradigm, cues associated with rewards through Pavlovian conditioning alter motivation and choice of instrumental actions. ... Predictive cues are an important part of our life that continuously influence and guide our actions. Hearing the sound of a horn makes us stop before we attempt to cross the street. Seeing an advertisement for fast food might make us hungry and lead us to seek out a specific type and source of food. In general, cues can both prompt us towards or stop us from engaging in a certain course of action. They can be adaptive (saving our life in crossing the street) or maladaptive, leading to suboptimal choices, e.g. making us eat when we are not really hungry (Colagiuri and Lovibond, 2015). In extreme cases they can even play a part in pathologies such as in addiction, where drug associated cues produce craving and provoke relapse (Belin et al., 2009).
^ abcdeBerridge 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. PMC3325516. PMID22487042. Incentive salience or 'wanting' is a specific form of Pavlovian-related motivation for rewards mediated by mesocorticolimbic brain systems ...Incentive salience integrates two separate input factors: (1) current physiological neurobiological state; (2) previously learned associations about the reward cue, or Pavlovian CS ... 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. In daily life, the smell of food may make you suddenly feel hungry, when you hadn't felt that way a minute before. In animal neuroscience experiments, a CS for reward may trigger a more frenzied pulse of increased instrumental efforts to obtain that associated UCS reward in situations that purify the measurement of incentive salience, such as in Pavlovian-Instrumental Transfer (PIT) experiments ... Similarly, including a CS can often spur increased consumption of a reward UCS by rats or people, compared to consumption of the same UCS when CSs are absent ... Thus Pavlovian cues can elicit pulses of increased motivation to consume their UCS reward, whetting and intensifying the appetite. However, the motivation power is never simply in the cues themselves or their associations, since cue-triggered motivation can be easily modulated and reversed by drugs, hungers, satieties, etc., as discussed below.
^ abcdefghijklCorbit LH, Balleine BW (2016). Learning and Motivational Processes Contributing to Pavlovian-Instrumental Transfer and Their Neural Bases: Dopamine and Beyond. Vol. 27. pp. 259–289. doi:10.1007/7854_2015_388. ISBN978-3-319-26933-7. PMID26695169. Such effects suggest that specific motivational states gate the arousing effects of Pavlovian incentives processes on instrumental performance ... Behavioral findings are supported by evidence that distinct neural circuits centered on the NAc core and shell mediate the general and specific forms of transfer, respectively ... Finally, stress has been shown to increase the magnitude of transfer effects, particularly general transfer, suggesting a shift in cognitive control under stress conditions. ... corticotropin-releasing factor (CRF) administered directly into the NAc shell enhances transfer in a dose-dependent fashion without affecting baseline lever-press performance (Pecina et al. 2006), suggesting that CRF amplifies the motivational impact of cued rewards in much the same manner as dopamine. ... In general, acute treatments seem to enhance transfer effects, whereas chronic treatments decrease transfer{{cite book}}: |journal= ignored (help)
^ abcdefghSalamone JD, Pardo M, Yohn SE, López-Cruz L, SanMiguel N, Correa M (2016). "Mesolimbic Dopamine and the Regulation of Motivated Behavior". Behavioral Neuroscience of Motivation. Vol. 27. pp. 231–257. doi:10.1007/7854_2015_383. ISBN978-3-319-26933-7. PMID26323245. Considerable evidence indicates that accumbens DA is important for Pavlovian approach and Pavlovian-to-instrumental transfer [(PIT)] ... PIT is a behavioral process that reflects the impact of Pavlovian-conditioned stimuli (CS) on instrumental responding. For example, presentation of a Pavlovian CS paired with food can increase output of food-reinforced instrumental behaviors, such as lever pressing. Outcome-specific PIT occurs when the Pavlovian unconditioned stimulus (US) and the instrumental reinforcer are the same stimulus, whereas general PIT is said to occur when the Pavlovian US and the reinforcer are different. ... More recent evidence indicates that accumbens core and shell appear to mediate different aspects of PIT; shell lesions and inactivation reduced outcome-specific PIT, while core lesions and inactivation suppressed general PIT (Corbit and Balleine 2011). These core versus shell differences are likely due to the different anatomical inputs and pallidal outputs associated with these accumbens subregions (Root et al. 2015). These results led Corbit and Balleine (2011) to suggest that accumbens core mediates the general excitatory effects of reward-related cues. PIT provides a fundamental behavioral process by which conditioned stimuli can exert activating effects upon instrumental responding{{cite book}}: |journal= ignored (help)
^Lamb RJ, Schindler CW, Pinkston JW (May 2016). "Conditioned stimuli's role in relapse: preclinical research on Pavlovian-Instrumental-Transfer". Psychopharmacology. 233 (10): 1933–1944. doi:10.1007/s00213-016-4216-y. PMC4863941. PMID26800688. Pavlovian learning plays a central role in many theories of addiction, particularly with regard to relapse. In broad terms, encountering drug-paired CSs are hypothesized to precipitate relapse, often, though not always, by increasing motivation to take drugs. Presumably, if a drug-paired CS increases motivation to take drugs, then a drug-paired CS should increase drug consumption.