Even though aging is associated with increased and prolonged episodes of pain, little is known about potential age-related changes in the "top-down" modulation of pain, such as cognitive distraction from pain. The hypoalgesic effect of distraction results from a competition for attentional and executive resources mediated by the prefrontal cortex (PFC). Given that age-related grey matter atrophy is particularly prominent in the PFC, older adults may benefit less from distraction to reduce pain than young adults. The aim of this study was to investigate the influence of aging on task-related hypoalgesia and its neural mechanisms, with a focus on the role of executive functions in distraction from pain.
64 participants (32 young adults: 26.69 ± 4.14 years; 32 older adults: 68.28 ± 7.00 years) first completed a battery of neuropsychological tests. In a second session, we administered a pain distraction paradigm while functional brain images were acquired. In this paradigm, participants completed a low (0-back) and a high (2-back) load condition of a working memory task while receiving either innocuous or painful heat stimuli to their lower arm. To control for age-related differences in sensitivity to pain and perceived task difficulty, stimulus intensity and task speed were individually calibrated.
Both age groups showed significantly reduced activity in a network of regions involved in pain processing when performing the high compared to the low load distraction task; however, young adults showed a larger neural distraction effect in several of these regions, including the insula, caudate and midcingulate cortex. Moreover, in older adults, better executive functions – in particular inhibitory control abilities – were associated with a larger neural distraction effect in the insula, thalamus and primary somatosensory cortex, and with more activation in several prefrontal cortex regions during the high load task.
These findings clearly demonstrate that the top-down control of pain is altered by age and could explain the higher vulnerability of older adults to developing chronic pain. Moreover, our findings suggest that the assessment of executive functions may be a useful tool for predicting the efficacy of cognitive pain modulation strategies in older adults
