Relief as a Reward: Hedonic and Neural Responses to Safety from Pain

Abstract

Relief fits the definition of a reward. Unlike other reward types the pleasantness of relief depends on the violation of a negative expectation, yet this has not been investigated using neuroimaging approaches. We hypothesized that the degree of negative expectation depends on state (dread) and trait (pessimism) sensitivity. Of the brain regions that are involved in mediating pleasure, the nucleus accumbens also signals unexpected reward and positive prediction error. We hypothesized that accumbens activity reflects the level of negative expectation and subsequent pleasant relief. Using fMRI and two purpose-made tasks, we compared hedonic and BOLD responses to relief with responses during an appetitive reward task in 18 healthy volunteers. We expected some similarities in task responses, reflecting common neural substrates implicated across reward types. However, we also hypothesized that relief responses would differ from appetitive rewards in the nucleus accumbens, since only relief pleasantness depends on negative expectations. The results confirmed these hypotheses. Relief and appetitive reward task activity converged in the ventromedial prefrontal cortex, which also correlated with appetitive reward pleasantness ratings. In contrast, dread and pessimism scores correlated with relief but not with appetitive reward hedonics. Moreover, only relief pleasantness covaried with accumbens activation. Importantly, the accumbens signal appeared to specifically reflect individual differences in anticipation of the adverse event (dread, pessimism) but was uncorrelated to appetitive reward hedonics. In conclusion, relief differs from appetitive rewards due to its reliance on negative expectations, the violation of which is reflected in relief-related accumbens activation.

Onset and offset of aversive events establish distinct memories requiring fear and reward networks

“…In Drosophila, such training establishes conditioned approach to the stimulus (Tanimoto et al 2004;Yarali et al 2008), indicating that it has been learned as a signal for "relief" from shock (Solomon 1980;Wagner 1981) or for "respite" (Lohr et al 2007) or "safety" (Sutton and Barto 1990;Chang et al 2003;Leknes et al 2011) related to the shock-free safe period within the shock-associated dangerous experimental context. The relief-based explanation appears more fitting in this case, because "safety conditioning" should rely on the strength of the context-shock association (e.g., Chang et al 2003) and on the length of the shock-free safe period following the stimulus (e.g., Moscovitch and LoLordo 1968), but neither of these seems to be the case in Drosophila (Yarali et al 2008).…”

Placebo improves pleasure and pain through opposite modulation of sensory processing

“…However, pain and pleasure processes are tightly linked. Relief from pain can induce a pleasant experience underpinned by activation of reward neurocircuitry (2)(3)(4). Moreover, a painful stimulus can even be perceived as pleasant when it represents relief from a more severe outcome (5).…”

Pain, Pleasure, and Unpleasure

“…Studies indicate that relief involves not only a reduction in pain; it involves pleasure (see Bastian and Leknes, and Hardcastle, this volume). Indeed, relief even from the threat of pain produces pleasure (Leknes et al 2011). We asked earlier whether either pain or pleasure is our default state, unnoticed or absent only to the extent that it is masked or eliminated by the other state.…”