Pain-specific modulation of hippocampal activity and functional connectivity during visual encoding.

Acute and chronic pain automatically attract attention and thus interfere with cognitive functioning. Impaired memory is a prominent complaint of patients with chronic pain that substantially contributes to pain-related disability. In this fMRI study, we investigated the specific influence of pain on neural processes of memory encoding in healthy human volunteers using a visual task. To investigate the specificity of the interruptive effect of pain on the encoding of visual objects, objects were presented (1) alone, (2) with painful heat stimuli, or (3) with auditory stimuli that were matched for unpleasantness to the heat stimuli. The interruptive effect of concomitant aversive stimulation on behavioral measures and neural processing was assessed in a categorization task during encoding and in a subsequent recognition task. Pain interfered with object processing and encoding of visual stimuli. On the behavioral level, this resulted in slower reaction times during the categorization task for pain compared with auditory stimuli and in a lower recognition rate in the pain condition but not in the tone condition. Pain catastrophizing amplified this interruptive effect of pain. On the neural level, this pain-related disruption of encoding was associated with reduced activity in the right anterior hippocampus during encoding. Moreover, the hippocampus exhibited reduced functional connectivity with extrastriate regions during painful stimulation relative to auditory stimulation. In summary, our results show a pain-related disruption of visual encoding over and above the unpleasantness of a stimulus, suggesting a pain-specific interruptive mechanism that interferes with an early stage of memory formation.