Cortical excitability and multifidus activation responses to transcranial direct current stimulation in patients with chronic low back pain during remission

Evidence indicates that patients with chronic low back pain (CLBP) have lumbar multifidus muscle (LM) activation deficit which might be caused by changes in cortical excitability. Anodal transcranial direct current stimulation (a-tDCS) can be used to restore cortical excitability. This study aimed to (1) determine the immediate effects of a-tDCS on the cortical excitability and LM activation and (2) explore the relationship between cortical excitability and LM activation. Thirteen participants with CLBP during remission and 11 healthy participants were recruited. Cortical excitability (peak-to-peak motor evoked potential amplitude; P2P and cortical silent period; CSP) and LM activation were measured at pre- and post-intervention. We found significant difference (P < 0.05) in P2P between groups. However, no significant differences (P > 0.05) in P2P, CSP and LM activation were found between pre- and post-intervention in CLBP. The CLBP group demonstrated significant correlation (P = 0.05) between P2P and LM activation. Although our finding demonstrates change in P2P in the CLBP group, one-session of a-tDCS cannot induce changes in cortical excitability and LM activation. However, moderate to strong correlation between P2P and LM activation suggests the involvement of cortical level in LM activation deficit. Therefore, non-significant changes could have been due to inadequate dose of a-tDCS.

A Preliminary Investigation into the Neural Correlates of Knee Loading during a Change of Direction Task in Individuals after Anterior Cruciate Ligament Reconstruction

Background

Central nervous system (CNS) function after ACLR, quantified by the blood oxygen level dependent (BOLD) response, is altered in regions of sensory function during knee movement after ACLR. However, it is unknown how this altered neural response may manifest in knee loading and response to sensory perturbations during sport specific movements.

Purpose

To investigate the relationship among CNS function and lower extremity kinetics, under multiple visual conditions, during 180° change of direction task in individuals with a history of ACLR.

Methods

Eight participants, 39.3 ± 37.1 months after primary, left ACLR performed repetitive active knee flexion and extension of their involved knee during fMRI scanning. Participants separately performed 3D motion capture analysis of a 180° change of direction task under full vision (FV) and stroboscopic vision (SV) conditions. A neural correlate analysis was performed to associate BOLD signal to knee loading of the left lower extremity.

Results

Involved limb peak internal knee extension moment (pKEM) was significantly lower in the SV condition (1.89 ± 0.37 N*m/Kg) compared to the FV condition (2.0 ± 0.34 N*m/Kg) (p = .018). Involved limb pKEM during the SV condition was positively correlated with BOLD signal in the contralateral precuneus and superior parietal lobe (Voxels: 53; p = .017; z-stat max: 6.47; MNI peak: 6, -50, 66).

Conclusion

There is a positive association between involved limb pKEM in the SV condition and BOLD response in areas of visual-sensory integration. Activation of contralateral precuneus and superior parietal lobe brain regions may be a strategy to maintain joint loading when vision is perturbed.

Level of Evidence

Level 3.

Does central nervous system dysfunction underlie patellofemoral pain in young females? Examining brain functional connectivity in association with patient-reported outcomes

Patellofemoral pain (PFP) is defined as retro- or peri-patellar knee pain without a clear structural abnormality. Unfortunately, many current treatment approaches fail to provide long-term pain relief, potentially due to an incomplete understanding of pain-disrupted sensorimotor dysfunction within the central nervous system. The purposes of this study were to evaluate brain functional connectivity in participants with and without PFP, and to determine the relationship between altered brain functional connectivity in association with patient-reported outcomes. Young female patients with PFP (n = 15; 14.3 ± 3.2 years) completed resting-state functional magnetic resonance imaging (rs-fMRI) and patient-reported outcome measures. Each patient with PFP was matched with two controls (n = 30, 15.5 ± 1.4 years) who also completed identical rs-fMRI testing. Six bilateral seeds important for pain and sensorimotor control were created, and seed-to-voxel analyses were conducted to compare functional connectivity between the two groups, as well as to determine the relationship between connectivity alterations and patient-reported outcomes. Relative to controls, patients with PFP exhibited altered functional connectivity between regions important for pain, psychological functioning, and sensorimotor control, and the connectivity alterations were related to perceived disability, dysfunction, and kinesiophobia. The present results support emergent evidence that PFP is not localized to structural knee dysfunction, but may actually be resultant to altered central neural processes. Clinical significance: These data provide potential neuro-therapeutic targets for novel therapies aimed to reorganize neural processes, improve neuromuscular function, and restore an active pain-free lifestyle in young females with PFP.

Integrated 3D motion analysis with functional magnetic resonance neuroimaging to identify neural correlates of lower extremity movement

BACKGROUND

To better understand the neural drivers of aberrant motor control, methods are needed to identify whole brain neural correlates of isolated joints during multi-joint lower-extremity coordinated movements. This investigation aimed to identify the neural correlates of knee kinematics during a unilateral leg press task.

NEW METHOD

The current study utilized an MRI-compatible motion capture system in conjunction with a lower extremity unilateral leg press task during fMRI. Knee joint kinematics and brain activity were collected concurrently and averaged range of motion were modeled as covariates to determine the neural substrates of knee out-of-plane (frontal) and in-plane (sagittal) range of motion.

RESULTS

Increased out-of-plane (frontal) range of motion was associated with altered brain activity in regions important for attention, sensorimotor control, and sensorimotor integration (z >3.1, p < .05), but no such correlates were found with in-plane (sagittal) range of motion (z >3.1, p > .05). Comparison with Existing Method(s): Previous studies have either presented overall brain activation only, or utilized biomechanical data collected outside MRI in a standard biomechanics lab for identifying single-joint neural correlates.

CONCLUSIONS

The study shows promise for the MRI-compatible system to capture lower-extremity biomechanical data collected concurrently during fMRI, and the present data identified potentially unique neural drivers of aberrant biomechanics. Future research can adopt these methods for patient populations with CNS-related movement disorders to identify single-joint kinematic neural correlates that may adjunctively supplement brain-body therapeutic approaches.

Neural Correlates of Knee Extension and Flexion Force Control: A Kinetically-Instrumented Neuroimaging Study

Background: The regulation of muscle force is a vital aspect of sensorimotor control, requiring intricate neural processes. While neural activity associated with upper extremity force control has been documented, extrapolation to lower extremity force control is limited. Knowledge of how the brain regulates force control for knee extension and flexion may provide insights as to how pathology or intervention impacts central control of movement.

Objectives: To develop and implement a neuroimaging-compatible force control paradigm for knee extension and flexion.

Methods: A magnetic resonance imaging (MRI) safe load cell was used in a customized apparatus to quantify force (N) during neuroimaging (Philips Achieva 3T). Visual biofeedback and a target sinusoidal wave that fluctuated between 0 and 5 N was provided via an MRI-safe virtual reality display. Fifteen right leg dominant female participants (age = 20.3 ± 1.2 years, height = 1.6 ± 0.10 m, weight = 64.8 ± 6.4 kg) completed a knee extension and flexion force matching paradigm during neuroimaging. The force-matching error was calculated based on the difference between the visual target and actual performance. Brain activation patterns were calculated and associated with force-matching error and the difference between quadriceps and hamstring force-matching tasks were evaluated with a mixed-effects model (z > 3.1, p < 0.05, cluster corrected).

Results: Knee extension and flexion force-matching tasks increased BOLD signal among cerebellar, sensorimotor, and visual-processing regions. Increased knee extension force-matching error was associated with greater right frontal cortex and left parietal cortex activity and reduced left lingual gyrus activity. Increased knee flexion force-matching error was associated with reduced left frontal and right parietal region activity. Knee flexion force control increased bilateral premotor, secondary somatosensory, and right anterior temporal activity relative to knee extension. The force-matching error was not statistically different between tasks.

Conclusion: Lower extremity force control results in unique activation strategies depending on if engaging knee extension or flexion, with knee flexion requiring increased neural activity (BOLD signal) for the same level of force and no difference in relative error. These fMRI compatible force control paradigms allow precise behavioral quantification of motor performance concurrent with brain activity for lower extremity sensorimotor function and may serve as a method for future research to investigate how pathologies affect lower extremity neuromuscular function.

VALIDITY OF AN MRI-COMPATIBLE MOTION CAPTURE SYSTEM FOR USE WITH LOWER EXTREMITY NEUROIMAGING PARADIGMS

Background

Emergent linkages between musculoskeletal injury and the nervous system have increased interest to evaluate brain activity during functional movements associated with injury risk. Functional magnetic resonance imaging (fMRI) is a sophisticated modality that can be used to study brain activity during functional sensorimotor control tasks. However, technical limitations have precluded the precise quantification of lower-extremity joint kinematics during active brain scanning. The purpose of this study was to determine the validity of a new, MRI-compatible motion tracking system relative to a traditional multi-camera 3D motion capture system for measuring lower extremity joint kinematics.

Methods

Fifteen subjects (9 females, 6 males) performed knee flexion-extension and leg press movements against guided resistance while laying supine. Motion tracking data were collected simultaneously using the MRI-compatible and traditional multi-camera 3D motion systems. Participants' sagittal and frontal plane knee angles were calculated from data acquired by both multi-camera systems. Resultant range of angular movement in both measurement planes were compared between both systems. Instrument agreement was assessed using Bland-Altman plots and intraclass correlation coefficients (ICC).

Results

The system demonstrated excellent validity in the sagittal plane (ICCs>0.99) and good to excellent validity in the frontal plane (0.84 < ICCs < 0.92). Mean differences between corresponding range of angular movement measurements ranged from 0.186 ° to 0.295 °.

Conclusions

The present data indicate that this new, MRI-compatible system is valid for measuring lower extremity movements when compared to the gold standard 3D motion analysis system. As there is growing interest regarding the neural substrates of lower extremity movement, particularly in relation to injury and pathology, this system can now be integrated into neuroimaging paradigms to investigate movement biomechanics and its relation to brain activity.

Level of Evidence

3.

Real-time biofeedback integrated into neuromuscular training reduces high-risk knee biomechanics and increases functional brain connectivity: A preliminary longitudinal investigation

Prospective evidence indicates that functional biomechanics and brain connectivity may predispose an athlete to an anterior cruciate ligament injury, revealing novel neural linkages for targeted neuromuscular training interventions. The purpose of this study was to determine the efficacy of a real-time biofeedback system for altering knee biomechanics and brain functional connectivity. Seventeen healthy, young, physically active female athletes completed 6 weeks of augmented neuromuscular training (aNMT) utilizing real-time, interactive visual biofeedback and 13 served as untrained controls. A drop vertical jump and resting state functional magnetic resonance imaging were separately completed at pre- and posttest time points to assess sensorimotor adaptation. The aNMT group had a significant reduction in peak knee abduction moment (pKAM) compared to controls (p = .03, d = 0.71). The aNMT group also exhibited a significant increase in functional connectivity between the right supplementary motor area and the left thalamus (p = .0473 after false discovery rate correction). Greater percent change in pKAM was also related to increased connectivity between the right cerebellum and right thalamus for the aNMT group (p = .0292 after false discovery rate correction, r²  = .62). No significant changes were observed for the controls (ps > .05). Our data provide preliminary evidence of potential neural mechanisms for aNMT-induced motor adaptations that reduce injury risk. Future research is warranted to understand the role of neuromuscular training alone and how each component of aNMT influences biomechanics and functional connectivity.

A Novel Approach to Evaluate Brain Activation for Lower Extremity Motor Control

BACKGROUND AND PURPOSE

The purpose of this study was to assess the consistency of a novel MR safe lower extremity motor control neuroimaging paradigm to elicit reliable sensorimotor region brain activity.

METHODS

Participants completed multiple sets of unilateral leg presses combining ankle, knee, and hip extension and flexion movements against resistance at a pace of 1.2 Hz while lying supine in a 3T MRI scanner. Regions of Interest (ROI) consisted of regions primarily involved in lower extremity motor control (right and left primary motor cortex, primary somatosensory cortex, premotor cortex, secondary somatosensory cortex, basal ganglia, and the cerebellum).

RESULTS

The group analysis based on mixed effects paired samples t-test revealed no differences for brain activity between sessions (P > .05). Intraclass correlation coefficients in the sensorimotor regions were good to excellent for average percent signal change (.621 to .918) and Z-score (.697 to .883), with the exception of the left secondary somatosensory cortex percent signal change (.165).

CONCLUSIONS

These results indicate that a loaded lower extremity force production and attenuation task that simulates the range of motion of squatting, stepping, and landing from a jump is reliable for longitudinal neuroimaging applications and support the use of this paradigm in further studies examining therapeutic interventions and changes in dynamic lower extremity motor function.