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Dr Ben Seymour, Computational and Biological Learning Lab, Trumpington Street, Cambridge CB2 1PZ

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Center for Information and Neural Networks, National Institute for Information and Communications Technology (NICT), 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.

bjs49 AT cam.ac.uk / seymour AT cinet.jp

F1000 reviews (paywall)

 

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Monday
May062013

Relief ≠ reward

It’s tempting to assume that since relief of something bad (such as pain) is pleasant, then relief can be considered the same as other rewards, including when it comes to brain processes. This would be very convenient, since it would mean we could apply everything we know about reward processing to pain relief processing. But is it true?

 

Well, there is obvious parity in terms of valence: as long as we can show that relief motivates behaviour, then it is by a psychological definition a reward. But this relationship turns out to have a more nuanced history in theories of motivation and opponency - the approach-withdrawal yin-yang of reward and punishment systems. In Konorski’s classic account, relief and disappointment are inhibitory states that signify omission of otherwise expected punishment or reward, respectively. In Solomon and Corbit’s opponency model, interruption or terminatation of a punishment or reward is considered in a similar manner. Furthermore, that relief can motivate behaviour lay at the heart of (Mowrer’s) classic two-factor theory of avoidance: when one learns that a certain action reduces punishment, the outcome state that signals its relief becomes ‘rewarding’ (as a conditioned inhibitor), and then reinforces avoidance actions in the conventional manner (as a conditioned reinforcer). So far so good.

 

But flies can be seen circling the ointment when one notices the conspicuous paucity of good evidence that conditioned inhibitors can easily act as conditioned reinforcers. Furthermore, conditioned inhibitors sometimes seem to have different properties – they are remarkably resistant to extinction for instance, unlike reward excitators (i.e. normal reward-predicting cues). This raises an awkward possibility: perhaps relief might actually be a fundamentally different process

 

Two recent papers hint at some neurophysiological support to this hypothesis. Sangha and colleagues compare responses in rat amygdala neurons in a Palvovian learning task involving different cues associated with shock, safety and reward. They show neurons in the amygdala show selective cue responses discriminating the predictions of each. Although some neurons responded similarly to reward and safety, many neurons responded differentially.  In another paper, Fernando and colleagues compared behavioural and pharmacological properties of appetitive conditioned excitators (normal Pavlovian reward predictors) and aversive conditioned inhibitors (safety signals), and showed that whereas reward predictors support the acquisition of a new response, safety signals did not. Furthermore, systemic d-amphetamine boosted only reward-predicting instrumental behaviour, suggesting a selective role for dopamine in reward behaviour and not safety signal behaviour. Taken together, these results provide behavioural, electrophysiological and pharmacological evidence against the motivational equivalence of relief and reward.

 

This suggests that pain neuroscientists should cautious about equating relief and reward, and hopefully this should stimulate more research aimed at understanding the neural basis for of relief, including the possible differences between different types of relief (omission of expected pain, and termination of ongoing pain). It’s also important for understanding conditions such as Obsessive Compulsive Disorder, which is thought to be an inflation of avoidance ‘habits’ – over-activity of the system that supports maintenance of avoidance.

 

Safety encoding in the basal amygdala. Sangha S, Chadick JZ, Janak PH. J Neurosci. 2013 Feb 27;33(9):3744-51. PMID: 23447586 

Comparison of the conditioned reinforcing properties of a safety signal and appetitive stimulus: effects of d-amphetamine and anxiolytics. Fernando AB, Urcelay GP, Mar AC, Dickinson A, Robbins T. Psychopharmacology (Berl). 2013 May;227(2):195-208. PMID: 23299096

 

This blog is based on a recently published F1000 review with Hiro Mano.

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