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Kelly M Naugle,1 Yenisel Cruz-Almeida,2,3 Roger B Fillingim,2,4 Roland Staud,2,5 Joseph L Riley III2,4 1Department of Kinesiology, School of Physical Education and Tourism Management, Indiana University – Purdue University Indianapolis, Indianapolis, IN, 2Pain Research and Intervention Center of Excellence, University of Florida, 3Department of Aging and Geriatric Research, College of Medicine, 4Department of Community Dentistry and Behavioral Science, 5Department of Medicine, College of Medicine, University of Florida, Gainesville, FL, USA Abstract: Temporal summation (TS) of pain protocols typically involve the delivery of brief repetitive noxious stimuli held at a constant intensity and measuring the consequent increase in the perceived intensity of pain sensations. To date, no studies have examined the effect of a TS protocol on the perceived spatial dimensions of the pain experience and its interaction with age. This study used a new TS protocol that examined changes in the perceived size of the painful area in 22 younger adults and 20 older adults. Four trials of ten brief heat pulses delivered at a constant intensity were administered on the volar forearm. Interpulse intervals (IPIs) were 2.5 seconds or 3.5 seconds. Subjects rated the peak pain intensity (trials 1 and 3) or the size of the painful area (trials 2 and 4) after each pulse on a 0–100 scale. The magnitude of summation was calculated for each trial. Three seconds and 6 seconds after delivering the last heat pulse, the subjects rated the intensity or the size of any remaining pain (aftersensations). The results indicated that older adults compared to younger adults exhibited significantly greater summation of size ratings for the 2.5-second and 3.5-second IPI trials and size of pain aftersensations at 3 seconds following the 2.5-second IPI TS trial. These results suggest that aging is associated with enhanced endogenous facilitation of the perceived size of pain. The potential clinical and mechanistic implications of enhanced TS of size of pain remain unknown and warrant further investigation. Keywords: pain modulation, aging, elderly, pain facilitation, size of pain |
