• Chantal Villemure, Audrey C Laferrière, and M Catherine Bushnell.
• Alan Edwards Centre for Resaerch on Pain, McGill University, Montreal, Quebec.
• Pain Res Manag. 2012 Mar 1; 17 (2): 69-74.

BackgroundThe ventral striatum, particularly the nucleus accumbens, is commonly associated with the processing of reward and positive stimuli, positive affect as well as antinociceptive processes.ObjectivesThe present study examined whether the ventral striatum is implicated in analgesia resulting from positive mood change induced by pleasant odours.MethodsFunctional magnetic resonance imaging studies were conducted in healthy individuals receiving painful heat stimuli in the presence of pleasant or unpleasant odours, which were used to induce positive and negative mood states. Ventral striatum activity was examined in the two mood states.ResultsFor most subjects, pleasant odours improved mood and reduced pain unpleasantness perception relative to unpleasant odours. In the pleasant odour condition, the maximum activation of both the left and right ventral striatum was positively correlated with the amount of pain reduction. Furthermore, the left and right ventral striatum activations positively covaried with one another, and the right ventral striatum activation positively correlated with that in the periaqueductal grey matter. Both ventral striatum activations negatively covaried with the activation of the right mediodorsal thalamus, left dorsal anterior cingulate cortex, left medial prefrontal cortex and right ventrolateral prefrontal cortex.ConclusionsBecause both the mediodorsal thalamus and anterior cingulate are involved in pain affect perception, and activation within the prefrontal areas and periaqueductal grey matter were previously shown to correlate with mood-related pain modulation, it is concluded that the ventral striatum is likely implicated in the analgesic effect of positive mood changes induced by pleasant odours on pain unpleasantness.

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