Cognitive modulation of pain-related brain responses depends on behavioral strategy.

Interactions of pain and cognition have been studied in humans and animals previously, but the relationship between such behavioral interactions and brain activity is unknown. We aimed to show using functional MRI (fMRI) how a cognitively demanding task (Stroop) modulates pain-related brain activations and conversely, how pain modulates attention-related activity. Reaction time data indicated two types of pain responders: subjects in the A group had a faster Stroop reaction time when pain was concomitant to the attention task, while those in the P group had a slower Stroop performance during painful stimulation. fMRI data obtained during Stroop performance with and without noxious stimulation were subjected to region of interest analyses. We first tested whether brain activity during painful median nerve stimulation was modulated by cognitive load. We next tested whether brain activity during the high conflict cognitive task was modulated by pain. Pain-related activity in three regions, primary (S1), and secondary (S2) somatosensory cortices, and anterior insula, was attenuated by cognitive engagement, but this effect was specific to the A group. Pain-related activations in the caudal and rostral anterior cingulate cortex (ACC) and ventroposterior thalamus were not modulated by cognitive load. None of the areas showing attention-related responses, including bilateral dorsolateral prefrontal and posterior parietal cortices, were modulated by pain. These findings suggest that cortical regions associated with pain can be modulated by cognitive strategies. Furthermore, the distinction of behavioral subgroups may relate to cognitive coping strategies taken by patients with chronic pain.