The effects of manipulating the inter-stimulus-interval on heat-evoked temporal summation of second pain across the age span.

This study examined the effects of inter-stimulus-interval (ISI) on heat-evoked temporal summation of second pain (TSSP) and tested whether greatest maintenance of TSSP would occur at longer ISIs in older adults. Several lines of evidence support that TSSP is associated with central sensitization and is centrally mediated. The participants were 198 community- dwelling adults divided into three age cohorts (18-39, 40-59; and 60-78 years of age). Six TSSP trials used a train of 10 contacts with a preheated probe that made repetitive contact with the volar forearm. Participants completed two trials at each ISI of 2.5-sec. 3.5-sec and 4.5-sec. The intraclass correlations for each pair of trials support the reliability of the current methodology. TSSP scores declined in a time dependent manner across ISI. In addition, greater maintenance of TSSP at longer ISIs was observed in middle-aged and older age groups compared to the younger cohort. Significant associations were found between TSSP and measures of recent pain. Greater summation at longer ISIs in older adults would suggest slower decay of excitability in spinal neurons and infer increased risk for central sensitization with advancing age.