Mapping the neural mechanisms of spatial summation of pain in humans

• Applicant: Dr. Waclaw Adamczyk, Ph.D.
• Subject Area: Human Cognitive and Systems Neuroscience ; Biological Psychology and Cognitive Neuroscience
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574729638

Pain is a dynamic perceptual state emerging from distributed neural activity along the neuroaxis. One key—but poorly understood—psychophysical phenomenon is spatial summation of pain (SSP), wherein perceived pain intensity increases with the spatial extent of nociceptive input. Spatial summation plays a fundamental role in encoding stimulus magnitude: if summation is diminished, localized injuries may be under-perceived, risking tissue damage; conversely, amplified summation may lead to disproportionate pain from small nociceptive sources, a hallmark of chronic pain. Despite over 90 years of research, clinical and theoretical importance of SSP, the mechanisms underlying this effect remain poorly understood. The primary aim of this project is to provide a comprehensive yet focused investigation of the brain mechanisms underlying SSP. This will be achieved by employing state-of-the-art psychophysical examinations and cutting-edge functional magnetic resonance imaging (fMRI) to capture neural correlates of SSP. The project will address brain responses from both cortical and sub-cortical areas, including the periaqueductal gray matter (PAG), a key structure involved in pain modulation. fMRI and psychophysical assessments will be performed in both healthy individuals and patients with chronic widespread and localized back pain. Secondary research questions will address modality, intensity, positioning, and body site exposed to stimulation. In total, 180 participants (90 patients) will take part in the main research, and 15 individuals will participate in pilot studies. Previous research has shown that spatial summation is sub-additive and does not follow arithmetic principles. This project aims to observe neural mechanisms of SSP sub-additivity, particularly in subcortical structures. The active engagement of descending pain modulatory circuits in the brain could explain SSP phenomena, offering novel insights for treating pain states where this mechanism is likely impaired.

• DFG Programme: Research Grants