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. 2008 Oct;12(7):866-9.
doi: 10.1016/j.ejpain.2007.12.007. Epub 2008 Jan 28.

Signal valence in the nucleus accumbens to pain onset and offset

Lino Becerra  1 , David Borsook
Affiliations

Signal valence in the nucleus accumbens to pain onset and offset

Lino Becerra et al. Eur J Pain. 2008 Oct.

Abstract

Pain and relief are at opposite ends of the reward-aversion continuum. Studying them provides an opportunity to evaluate dynamic changes in brain activity in reward-aversion pathways as measured by functional magnetic resonance imaging (fMRI). Of particular interest is the nucleus accumbens (NAc), a brain substrate known to be involved in reward-aversion processing, whose activation valence has been observed to be opposite in response to reward or aversive stimuli. Here we have used pain onset (aversive) and pain offset (rewarding) involving a prolonged stimulus applied to the dorsum of the hand in 10 male subjects over 120s to study the NAc fMRI response. The results show a negative signal change with pain onset and a positive signal change with pain offset in the NAc contralateral to the stimulus. The study supports the idea that the NAc fMRI signal may provide a useful marker for the effects of pain and analgesia in healthy volunteers.

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Figures

Figure 1
Figure 1. Prolonged Heat Stimulus: Activation profile in the NAc
Top Panel – Multiwave model of response to a prolonged heat stimulus. A series of 9 waves (HR) was used to analyze the BOLD response to a prolonged heat stimulus (blue shaded area). An extra wave was added after the stimulus finished in order to capture any “relief” response. The blue background represents the time that the heat stimulus (46°C) was presented. Middle Panel –Amplitude and direction of response in the NAC with a multiwave model. The amplitude of each wave in the NAC is displayed against wave number. The first and last (relief) waves show significant positive response in the NAC. Waves 2–8 (the “late” response) show negative signal change in the NAc. Shaded area = noxious stimulus. Lower Panel - The figure shows statistical maps of activation within the NAc following the onset (initial pain) of a noxious painful stimulus (46°C) and after the pain has stopped (pain relief). Note that aversive stimulus produces a decrease in signal (blue) change while the rewarding stimulus produces an increase (red) in signal within the change structure. Data are averaged for 10 subjects (p<0.001, t-test).
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References

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