Predicting Value of Pain and Analgesia: Nucleus Accumbens Response to Noxious Stimuli Changes in the Presence of Chronic Pain

Neuron, Volume 66, Issue 1, 149-160, 15 April 2010  | 
Marwan N. Baliki,Paul Y. Geha,Howard L. Fields,A. Vania Apkarian

• • Copyright © 2010 Elsevier Inc. All rights reserved.  |  10.1016/j.neuron.2010.03.002
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  • Highlights
  • NAc predicts the reward value for expected pain relief in healthy subjects
  • NAc predicts the salience or arousal for imminent pain
  • Pain relief causes distinct NAc activities in healthy versus chronic pain subjects
  Summary
• We compared brain activations in response to acute noxious thermal stimuli in controls and chronic back pain (CBP) patients. Pain perception and related cortical activation patterns were similar in the two groups. However, nucleus accumbens (NAc) activity differentiated the groups at a very high accuracy, exhibiting phasic and tonic responses with distinct properties. Positive phasic NAc activations at stimulus onset and offset tracked stimulus salience and, in normal subjects, predicted reward (pain relief) magnitude at stimulus offset. In CBP, NAc activity correlated with different cortical circuitry from that of normals and phasic activity at stimulus offset was negative in polarity, suggesting that the acute pain relieves the ongoing back pain. The relieving effect was confirmed in a separate psychophysical study in CBP. Therefore, in contrast to somatosensory pathways, which reflect sensory properties of acute noxious stimuli, NAc activity in humans encodes its predicted value and anticipates its analgesic potential on chronic pain.