57: e2PD � electrical 2-point discrimination threshold to probe spatial acuity

Topic: Basic Science
Subtopic: Non-specific to any diagnosis (including studies in healthy animals), Electrophysiology, Assessment and Measurement of Pain/Nociception

Background and Aims: Testing spatial acuity is a useful tool to understand how the nervous system integrates sensory information. Usually this is done by measures like the 2-point discrimination threshold (2PDT). Chronic pain is often associated with impaired spatial acuity. However, the method to test spatial acuity suffers from several drawbacks. Many of these drawbacks are related to the mechanical stimulations typically used for testing, these handheld stimulations offers little control of stimulation parameters, limiting repeatability and high variance. In this study a method based on electrical stimulation in the lower leg is tested to compare its ability to assess spatial acuity.

Methods: 25 healthy participants (11 males, 27.8±8.2years) were included. Spatial acuity was assessed over the peroneus longus muscle in the lower leg. Spatial acuity (2PDT) was tested using conventional, mechanical calibers and compared to electrical stimulation (e2PD). Two different psycho-physical algorithms were compared, the method-of-limits (MoL) and the Psi method. Additionally, two response tasks were tested, a yes/no task where participants pushed a button when two points were perceived and a 1-interval, 2-alternative forced choice. Catch trials (1 point) were inserted as one in every four stimulations on average. The data was analyzed using a Linear-mixed model.

Results: The e2PD failed to estimate the threshold in several subjects due to reaching the limits of psychometrical algorithms. Conventional 2PDT was on average lower than e2PD. The average conventional 2PDTs were 41.6±2.8mm and 40.8±3.8mm respectively (Psi vs MoL) whereas the e2PD thresholds varied from 64.6±4.2mm for the Psi method with forced-choice to 76.7±4.6mm for the MoL with yes/no task. There was a significant difference between the conventional 2PDT and e2PD estimates of spatial acuity (LMM, p<0.05). But there were no significant differences within the conventional nor within the e2PD methods.

Conclusions: The failure to estimate the e2PD must be addressed in future studies, this may be possible but adding constraints to the psychometrical algorithms. The difference in the actual estimate of the two methods (conventional 2PDT vs e2PD), might not be a limitation of the e2PD method itself, but could prove translation from other, traditional methods more difficult. When taking each type of test separately (conventional 2PDT vs e2PD) it is encouraging that the use of different psychometrical methods does not appear to greatly affect the estimated threshold.

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Presenting Author: Ken Steffen Frahm
Submitting Author: Ken Steffen Frahm

Senior Author: Ken Steffen Frahm

IASP 2026 Global Year theme of Neuropathic Pain: No

• Jorgelina Leguizamon - Aalborg University
• Kristian Hennings: MSc, PhD - Inventors Way Aps, Aalborg, Denmark