663: Spatial summation of pain induced by remote nociceptive stimulation

Topic: Experimental (Non-clinical) Human Studies
Subtopic: Non -specific to any diagnosis, Psychology, Assessment and Measurement of Pain/Nociception, Pain mechanisms (e.g. descending inhibitory control, placebo, inflammation)

Background and Aims: Spatial summation of pain (SSp) refers to the psychophysical increase in perceived pain intensity as the spatial extent of nociceptive stimulation increases. Previous studies have demonstrated SSp when stimulation is distributed within a single dermatome or across adjacent dermatomes. However, it remains unclear whether stimulation applied to clearly remote body regions also elicits SSp. Here, we examined unilateral and bilateral SSp using electrocutaneous stimulation to determine whether spatially separated nociceptive inputs, including those delivered to opposite limbs, produce enhanced overall pain perception.

Methods: Thirty healthy participants completed a within-subject experiment in which they rated overall pain intensity during trials differing in the spatial extent of nociceptive stimulation (manipulated by the number of activated electrodes) and in electrode positioning: (i) unilateral or (ii) bilateral arm stimulation. During each 6-second trial, electrocutaneous stimuli were delivered at 20 Hz. Participants continuously rated pain using a computerised visual analogue scale (CoVAS). Pain intensity for each trial was quantified as the area under the curve (AUC), allowing assessment of the temporal dynamics of perceived pain.

Results: Strong evidence for unilateral SSp was observed. In unilateral trials, activation of three or four electrodes resulted in significantly greater pain AUC compared with single-electrode stimulation (p < 0.001). Importantly, bilateral trials in which four electrodes were distributed across both arms also produced robust SSp, yielding the highest pain AUC values relative to single-electrode conditions (p < 0.001). These findings indicate that increasing the spatial extent of nociceptive input enhances perceived pain intensity, even when stimulation is distributed across anatomically remote regions.

Conclusions: These findings demonstrate that SSp in humans is robust both within a single limb and across bilateral limbs. Spatially distributed nociceptive input from remote locations appears capable of engaging facilitatory mechanisms that outweigh potential inhibitory influences. This may have implications for understanding central mechanisms underlying spatial integration of pain, including processes related to conditioned pain modulation. Further research is required to clarify the neural substrates supporting bilateral spatial summation.

References: [1] Adamczyk, W. M., Manthey, L., Domeier, C., Szikszay, T. M., & Luedtke, K. (2021). Nonlinear increase of pain in distance-based and area-based spatial summation. Pain, 162(6), 1771–1780.
[2] Defrin, R., Tsedek, I., Lugasi, I., Moriles, I., & Urca, G. (2010). The interactions between spatial summation and DNIC: effect of the distance between two painful stimuli and attentional factors on pain perception. Pain, 151(2), 489–495.
[3] Douglass, D. K., Carstens, E., & Watkins, L. R. (1992). Spatial summation in human thermal pain perception: comparison within and between dermatomes. Pain, 50(2), 197–202.

Presenting Author: Wacław M. Adamczyk
Submitting Author: Waclaw Adamczyk

Senior Author: Wacław M. Adamczyk

IASP 2026 Global Year theme of Neuropathic Pain: No

• Jakub Nastaj: MSc - Laboratory of Pain Research, Institute of Physiotherapy and Health Sciences, Academy of Physical Education, Katowice, Poland
• Waclaw M. Adamczyk: PhD - Institute of Health Sciences, Pain and Exercise Research Luebeck (P.E.R.L.), Universität zu Lübeck, Luebeck, Germany