title: Cortical Sensorimotor Processing of Painful Pressure in Patients with Chronic Lower Back Pain-An Optical Neuroimaging Study using fNIRS.
abstract: In this study we investigated sensorimotor processing of painful pressure stimulation on the lower back of patients with chronic lower back pain (CLBP) by using functional near-infrared spectroscopy (fNIRS) to measure changes in cerebral hemodynamics and oxygenation. The main objectives were whether patients with CLBP show different relative changes in oxy- and deoxyhemoglobin ([O2Hb] and [HHb]) in the supplementary motor area (SMA) and primary somatosensory cortex (S1) compared to healthy controls (HC). Twelve patients with CLBP (32 ± 6.1 years; range: 24-44 years; nine women) and 20 HCs (33.5 ± 10.7 years; range 22-61 years; eight women) participated in the study. Painful and non-painful pressure stimulation was exerted with a thumb grip perpendicularly to the spinous process of the lumbar spine. A force sensor was attached at the spinous process in order to control pressure forces. Tactile stimulation was realized by a one-finger brushing. Hemodynamic changes in the SMA and S1 were measured bilaterally using a multi-channel continuous wave fNIRS imaging system and a multi-distant probe array. Patients with CLBP showed significant stimulus-evoked hemodynamic responses in [O2Hb] only in the right S1, while the HC exhibited significant [O2Hb] changes bilaterally in both, SMA and S1. However, the group comparisons revealed no significant different hemodynamic responses in [O2Hb] and [HHb] in the SMA and S1 after both pressure stimulations. This non-significant result might be driven by the high inter-subject variability of hemodynamic responses that has been observed within the patients group. In conclusion, we could not find different stimulus-evoked hemodynamic responses in patients with CLBP compared to HCs. This indicates that neither S1 nor the SMA show a specificity for CLBP during pressure stimulation on the lower back. However, the results point to a potential subgrouping regarding task-related cortical activity within the CLBP group; a finding worth further research.
authors.affiliation: Interdisciplinary Spinal Research, Department of Chiropractic Medicine, University Hospital BalgristZürich, Switzerland; Department of Health Sciences and Technology, Human Movement Sciences and Sport, ETH ZürichZürich, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Vrana
authors.affiliation: Interdisciplinary Spinal Research, Department of Chiropractic Medicine, University Hospital Balgrist Zürich, Switzerland.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Meier
authors.affiliation: Interdisciplinary Spinal Research, Department of Chiropractic Medicine, University Hospital Balgrist Zürich, Switzerland.
authors.forename: Sabina
authors.initials: S
authors.lastname: Hotz-Boendermaker
authors.affiliation: Interdisciplinary Spinal Research, Department of Chiropractic Medicine, University Hospital Balgrist Zürich, Switzerland.
authors.forename: Barry K
authors.initials: BK
authors.lastname: Humphreys
authors.affiliation: Biomedical Optics Research Laboratory (BORL), Department of Neonatology, University Hospital Zürich Zürich, Switzerland.
authors.forename: Felix
authors.initials: F
authors.lastname: Scholkmann
keywords: back pain; chronic pain; functional near-infrared spectroscopy; hemodynamic response; sensorimotor cortex