Neural correlates of lumbar tactile acuity in patients with non-specific low back pain and healthy controls – an MRI study

Background Tactile acuity is defined as the skin’s ability to discriminate spatial patterns of stimulation. The two-point discrimination (TPD) threshold is commonly used to assess tactile acuity in non-specific low back pain (nsLBP) [1]. Another approach, the two-point estimation (TPE) task [2], is more time-efficient and, therefore potentially suitable for clinical use. The TPD is closely linked to functional and structural reorganisation in the primary somatosensory cortices (S1) [3] [4], yet studies on neural correlates of TPE are lacking. This study aims to identify potential associations between outcomes of lumbar TPE and TPD and resting-state functional connectivity (rsFC) and structural connectivity (SC) of the S1 region.

Methods Preliminary data from the ongoing cross-sectional ‘PREDICT-LBP’ (PRedictive Evidence Driven Intelligent Classification Tool for Low Back Pain) study [5] are analysed. Whole-brain resting-state functional MRI (voxel size: 3mm isotropic; TE: 30; TR: 2500; acquisition time: 8:12min) and diffusion-weighted MRI (voxel size: 2mm isotropic, TE: 90; TR: 10000; 105 directions in 3 shells, b: 1000/1800/2500) are acquired with a 3T Philips Achieva MR system, providing rsFC and SC, respectively. MRI data processing is performed according to literature standards [6] [7]. To obtain SC, the deterministic tractography algorithm ‘SD_Stream’ from MRtrix3 [8] is performed to reconstruct white matter streamlines. To parcellate the brain into subregions, we use the ‘Brainnetome’ atlas [9] for both SC and rsFC. The lumbar TPD and TPE are measured at spinal level L4 with a digital calliper according to established protocols [2] [10]. The correlation of both SC and rsFC of the S1 region and the measures of tactile acuity are investigated using FDR-corrected univariate testing.

Results We have currently (August 2023 – June 2024) acquired data from 155 participants (111 with nsLBP and 44 healthy controls). Visual quality control and processing of MRI data is ongoing and preliminary results will be presented at FSPT 2024. We hypothesize similar findings in neural correlates of TPE and TPD.

Summary This work will be the first to investigate lumbar TPD and TPE for their atlas-based SC and rsFC correlates in adults with and without nsLBP. Researchers and clinicians will be informed as to whether TPD and/or TPE can be utilized as a clinical equivalent to S1 representation and reorganisation processes.

Publication History

Article published online:
21 May 2025

• Literature

• 1 Adamczyk W, Luedtke K, Saulicz E.. Lumbar Tactile Acuity in Patients With Low Back Pain and Healthy Controls: Systematic Review and Meta-Analysis. Clin J Pain 2018; 34: 82-94
• 2 Adamczyk WM, Sługocka A, Mehlich K, Saulicz E, Luedtke K.. Preliminary Validation of a Two-Point Estimation Task for the Measurement of Sensory Dissociation in Patients with Chronic Low Back Pain. Pain Med 2019; 20: 2472-8
• 3 Kim H, Mawla I, Lee J, Gerber J, Walker K, Kim J. et al. Reduced tactile acuity in chronic low back pain is linked with structural neuroplasticity in primary somatosensory cortex and is modulated by acupuncture therapy. NeuroImage 2020; 217: 116899
• 4 Haag LM, Heba S, Lenz M, Glaubitz B, Höffken O, Kalisch T. et al. Resting BOLD fluctuations in the primary somatosensory cortex correlate with tactile acuity. Cortex 2015; 64: 20-8
• 5 Belavy DL, Tagliaferri SD, Tegenthoff M, Enax-Krumova E, Schlaffke L, Bühring B. et al. Evidence- and data-driven classification of low back pain via artificial intelligence: Protocol of the PREDICT-LBP study. PLOS ONE 2023; 18: e0282346
• 6 Esteban O, Markiewicz CJ, Blair RW, Moodie CA, Isik AI, Erramuzpe A. et al. fMRIPrep: a robust preprocessing pipeline for functional MRI. Nat Methods 2019; 16: 111-6
• 7 Tax CMW, Bastiani M, Veraart J, Garyfallidis E, Okan Irfanoglu M.. What’s new and what’s next in diffusion MRI preprocessing. NeuroImage 2022; 249: 118830
• 8 Tournier JD, Smith R, Raffelt D, Tabbara R, Dhollander T, Pietsch M. et al. MRtrix3: A fast, flexible and open software framework for medical image processing and visualisation. NeuroImage. 2019; 202: 116137
• 9 Fan L, Li H, Zhuo J, Zhang Y, Wang J, Chen L. et al. The Human Brainnetome Atlas: A New Brain Atlas Based on Connectional Architecture. Cereb Cortex 2016; 26: 3508-26
• 10 Ehrenbrusthoff K, Ryan CG, Grüneberg C, Wolf U, Krenz D, Atkinson G. et al. The intra- and inter-observer reliability of a novel protocol for two-point discrimination in individuals with chronic low back pain. Physiol Meas 2016; 37: 1074-88