During COVID-19 pandemic associated with multiple restrictions research performance is significantly hampered. This experiment aimed to verify, whether it is possible to adapt the experimental pain induction technique and observe the spatial summation of pain (SSp) within the field-like environment (so that it is possible to conduct the experiment outside of the laboratory and obtain similar results). Two variants of the Cold Pressor Task (CPT) were chosen to induce the SSp effect: i) using a professional apparatus available in the laboratory and ii) with the use of a commercially available plastic box filled with ice and water and a thermometer to measure the temperature of the water. Volunteers’ (n = 9) hands were divided into 5 segments, which were then subsequently immersed in the cold water (5°C) for 60 seconds (5-minute intertrial interval). Each participant took part in two sessions, i.e., using laboratory equipment and its non-laboratory equivalent. Preliminary observations confirmed that it is possible to induce SSp using both laboratory devices and methods adapted to non-laboratory conditions. SSp effect size was found to be similar in both methods. Small differences in the level of reported pain were observed, but these differences did not affect the SSp effect. The study showed that it is possible to adapt the procedure to induce pain and SSp within non-laboratory environment.

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To calibrate or not to calibrate? This question is raised by almost everyone designing an experimental pain study with supra-threshold stimulation. The dilemma is whether to individualize stimulus intensity to the pain threshold / supra-threshold pain level of each participant or whether to provide the noxious stimulus at a fixed intensity so that everyone receives the identical input. Each approach has unique pros and cons which need to be considered to i) accurately design an experiment, ii) enhance statistical inference in the given data and, iii) reduce bias and the influence of confounding factors in the individual study e.g., body composition, differences in energy absorption and previous experience. Individualization requires calibration, a procedure already irritating the pain system but allowing to match the pain level across individuals. It leads to a higher variability of the stimulus intensity, thereby influencing the encoding of “noxiousness” reaching the central nervous system. Results might be less influenced by statistical phenomena such as ceiling/floor effects and the approach does not seem to rise ethical concerns. On the other hand, applying a fixed (standardized) intensity reduces the problem of intensity encoding leading to a large between-subjects variability in pain responses. Fixed stimulation intensities do not require pre-exposure. It can be proposed that one method is not preferable over another, however the choice depends on the study aim and the desired level of external validity. This paper discusses considerations for choosing the best approach for experimental pain studies and provides recommendations for different study designs.

Chronic pain is a treatment resistant condition and is characterized by functional and structural alterations in the central nervous system (CNS). Those changes are demonstrated by reorganization of the sensory cortex and loss of density in white and grey matter in CNS. The aim of this review was to introduce the sensory discrimination training (SDT), the new therapeutic approach, developed to reverse those changes. SDT is aimed at restoring tactile acuity through training the ability to discriminate sensory stimuli. The most often used forms of SDT are tactile stimuli localization, discrimination of those stimuli and graphaestesia. Our review concentrates on theoretical assumptions underlying the SDT, the most common sensory dysfunctions associated with chronic pain (e.g. tactile acuity changes) and some of the diagnostic methods. The exemplary forms of training in phantom limb pain, complex regional pain syndrome and chronic low back pain were described. In addition, review presents critical evaluation of scientific evidence of SDT in chronic pain, including available systematic reviews and experimental studies. Scientific evidence tends to support the application of SDT in chronic pain, although unambiguous conclusions related to its effectiveness, cannot be drawn. Extensive randomized controlled trials as well as basic research are strongly advised to be conducted, as they can provide knowledge about analgesic properties of SDT in patients and healthy subjects. Quantitative synthesis of available experimental studies is also recommended.

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 (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 (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.