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Reproducibility of spatial summation of pain effect during COVID-19 pandemic

The ongoing COVID-19 pandemic has led to many restrictions affecting the research conduct. The purpose of this study was to reproduce the previously observed spatial summation of pain effect (SSp) using non-laboratory procedures and commercial equipment. An additional aim was to measure the association between expectation and SSp for the first time. The Cold Pressor Task (CPT) was used to induce SSp. Healthy participants (N=68) immersed their non-dominant hands (divided into 5 segments) into cold water (Cold Pressor Task). Two conditions were used 1) gradual hand immersion (ascending condition) and 2) gradual hand withdrawal (descending condition). Pain intensity was measured on a Visual Analogue Scale (VAS). The influence of psychological factors, such as the volunteer’s expectation of pain intensity, on the actual perception of pain were also measured on a VAS. Results showed significant SSp (χw(4) = 116.9, p < 0.001), reproduced with non-laboratory equipment in a home-based set-up. Furthermore, two novel findings were observed: i) spatial summation increased with the increase in exposure to the noxious stimulus (χw(2) = 157.5, p < 0.001), ii) there was a significant correlation between expectation and perceived pain, indicating that pain expectations can contribute to SSp. Results showed that SSp is shaped by a mixture of excitatory and inhibitory mechanisms and is influenced by the sensitization of the nociceptive system. Moreover, spatial summation is influenced by expectation. This study proposes a new feasible way to induce SSp using a home-based set-up using the CPT during COVID-19.