Changes in cortical activation during upright stance in individuals with chronic low back pain: An fNIRS study

Abstract

Introduction: Postural control deficits are a potential cause of persistent and recurrent pain in patients with chronic low back pain (CLBP). Although some studies have confirmed that the dorsolateral prefrontal cortex (DLPFC) contributes to pain regulation in CLBP, its role in the postural control of patients with CLBP remains unclear. Therefore, this study aimed to investigate the DLPFC activation of patients with CLBP and healthy controls under different upright stance task conditions.

Methods: Twenty patients with CLBP (26.50 ± 2.48 years) and 20 healthy controls (25.75 ± 3.57 years) performed upright stance tasks under three conditions: Task-1 was static balance with eyes open; Task-2 was static balance with eyes closed; Task-3 involved dynamic balance on an unstable surface with eyes open. A wireless functional near-infrared spectroscopy (fNIRS) system measured cortical activity, including the bilateral DLPFC, pre-motor cortex (PMC) and supplementary motor area (SMA), the primary motor cortex (M1), the primary somatosensory cortex (S1), and a force platform measured balance parameters during upright stance.

Results: The two-way repeated measures ANOVA results showed significant interaction in bilateral PMC/SMA activation. Moreover, patients with CLBP had significantly increased right DLPFC activation and higher sway 32 area and velocity than healthy controls during upright stance.

Discussion: Our results imply that PMC/SMA and DLPFC maintain standing balance. The patients with CLBP have higher cortical activity and upright stance control deficits, which may indicate that the patients with CLBP have low neural efficiency and need more motor resources to maintain balance.

Keywords: balance; dorsolateral prefrontal cortex; functional near-infrared spectroscopy; low back pain; motor dysfunction.

FIGURE 1

(A) Diagram of three upright stance tasks. (B) fNIRS testing procedure. The TecnoBody system was used to collect the COP signals of each participant during the upright stance control task, and fNIRS technology was used to detect real-time hemodynamic signals. COP, center of pressure; fNIRS, functional near-infrared spectroscopy.

FIGURE 2

Brain map of the fNIRS head probe covering the prefrontal and parietal cortices. The purple circles represent near-infrared light source fibers. The blue circles represent detectors. The short gray lines represent the channels between the sources and detectors. The channels in the red dotted box represent the DLPFC. The channels in the blue dotted box represent the PMC/SMA. The channels in the green dotted box represent M1. The channels in the yellow dotted box cover S1. The MNI coordinates of the selected channel are provided in the right table. fNIRS, functional near-infrared spectroscopy; DLPFC, dorsolateral prefrontal cortex; M1, primary motor cortex; PMC/SMA, pre-motor cortex and supplementary motor area; S1, primary somatosensory cortex.

FIGURE 3

COP paraments for each group under three upright stance conditions. The box plot shows the median and the 25th and 75th quartiles of (A) AP velocity, (B) ML velocity, (C) sway area, and (D) sway length. Lower and upper error lines display the 5th and 95th percentiles. *Represents the interaction between group and condition, *p < 0.05; ^#represents the main effect of condition. CLBP, chronic lower back pain group; HC, healthy control group; AP velocity, anteroposterior velocity; ML velocity, mediolateral velocity.

FIGURE 4

Beta values of [HbO] concentration in eight ROIs of two groups under three conditions (A–H). (A) Left DLPFC; (B) right DLPFC; (C) left PMC/SMA; (D) right PMC/SMA; (E) left M1; (F) right M1; (G) left S1; and (H) right S1. The box plot shows the median and the 25 and 75th quartiles of beta value of [HbO] concentration. Lower and upper error lines display the 5 and 95th percentiles. *Represents the interaction between group and condition, *p < 0.05, **p < 0.01, and ***p < 0.001; ^#represents the main effect of condition, ^#p < 0.05. DLPFC, dorsolateral prefrontal cortex; fNIRS, functional near-infrared spectroscopy; M1, primary motor cortex; PMC/SMA, pre-motor cortex and supplementary motor area; S1, primary somatosensory cortex.