Crossing the line of pain: FMRI correlates of crossed-hands analgesia.

UNLABELLED: Crossing the hands over the body midline reduces the perceived intensity of nociceptive stimuli applied to the hands by impairing the ability to localize somatosensory stimuli. The neural basis of this "crossed-hands analgesia" has not been investigated previously, although it has been proposed that the effect may be modulated by multimodal areas. We used functional magnetic resonance imaging to test the hypothesis that crossed-hands analgesia is mediated by higher-order multimodal areas rather than by specific somatosensory ones. Participants lay in the scanner while mechanical painful stimuli were applied to their hands held in either a crossed or uncrossed position. They reported significantly lower perceived intensity of pain when their hands were crossed. Although activations elicited by stimuli applied to the crossed hands revealed significantly greater blood oxygen level-dependent responses in the anterior cingulate cortex, the insula, and the medial frontal gyrus, the blood oxygen level-dependent responses in the superior parietal lobe were greater with the hands uncrossed. Our results provide evidence that crossed-hands analgesia is mediated by higher-order frontoparietal multimodal areas involved in sustaining and updating body and spatial representations.

PERSPECTIVE: We found crossed-hands analgesia to be mediated by multimodal areas, such as the posterior parietal, cingulate, and insular cortices, implicated in space and body representation. Our findings highlight how the perceived intensity of painful stimuli is shaped by how we represent our body and the space surrounding it.