Upper limb motor dysfunction is associated with fragmented kinetics after brain injury.

BACKGROUND: Characterization of motor deficits after brain injury is important for rehabilitation personalization. While studies reported abnormalities in the kinematics of paretic and non-paretic elbow extension for patients with brain injuries, kinematic analysis is not sufficient to explore how patients deal with musculoskeletal redundancy and the energetic aspect of movement execution. Conversely, interarticular coordination and movement kinetics can reflect patients' motor strategies. This study investigates motor strategies of paretic and non-paretic upper limb after brain injury to highlight motor deficits or compensation strategies. METHODS: 26 brain-injured hemiplegic patients and 24 healthy controls performed active elbow extensions in the horizontal plane, with both upper limbs for patients and, with the dominant upper limb for controls. Elbow and shoulder kinematics, interarticular coordination, net joint kinetics were quantified. FINDINGS: Results show alterations in kinematics, and a strong correlation between elbow and shoulder angles, as well as time to reach elbow and shoulder peak angular velocity in both upper limbs of patients. Net joint kinetics were lower for paretic limb and highlighted a fragmented motor strategy with increased number of transitions between concentric and eccentric phases. INTERPRETATION: In complement to kinematic results, our kinetic results confirmed patients' difficulties to manage both spatially and temporally the joint degrees of freedom redundancy but revealed a fragmented compensatory motor strategy allowing patients upper limb extension despite quality alteration and decrease in energy efficiency. Motor rehabilitation should improve the management of this fragmentation strategy to improve the performance and the efficiency of active movement after brain injury.

Biomechanical modeling for the estimation of muscle forces: toward a common language in biomechanics, medical engineering, and neurosciences.

Different research fields, such as biomechanics, medical engineering or neurosciences take part in the development of biomechanical models allowing for the estimation of individual muscle forces involved in motor action. The heterogeneity of the terminology used to describe these models according to the research field is a source of confusion and can hamper collaboration between the different fields. This paper proposes a common language based on lexical disambiguation and a synthesis of the terms used in the literature in order to facilitate the understanding of the different elements of biomechanical modeling for force estimation, without questioning the relevance of the terms used in each field or the different model components or their interest. We suggest that the description should start with an indication of whether the muscle force estimation problem is solved following the physiological movement control (from the nervous drive to the muscle force production) or in the opposite direction. Next, the suitability of the model for force production estimation at a given time or for monitoring over time should be specified. Authors should pay particular attention to the method description used to find solutions, specifying whether this is done during or after data collection, with possible method adaptations during processing. Finally, the presence of additional data must be specified by indicating whether they are used to drive, assist, or calibrate the model. Describing and classifying models in this way will facilitate the use and application in all fields where the estimation of muscle forces is of real, direct, and concrete interest.

Intermuscular coherence of plantar and dorsiflexor muscles in older adults with Parkinson's disease and age-matched controls during bipedal and unipedal stance.

Introduction: Postural instability increases with age and is exacerbated in neurological disorders such as Parkinson's disease (PD). Reducing the base of support from bipedal to unipedal stance increases center of pressure (CoP) parameters and intermuscular coherence in lower-leg muscles of healthy older adults. To further develop an understanding of postural control in an altered state of neurological impairment, we explored intermuscular coherence in lower-leg muscles and CoP displacement in older adults with PD. Methods: This study measured surface EMG from the medial (MG) and lateral (LG) gastrocnemii, soleus (SOL), and tibialis anterior (TA), and examined EMG amplitude and intermuscular coherence during bipedal and unipedal stance on a force plate with firm (no foam) and compliant (standing on foam) surface conditions in nine older adults with PD (70±5 years, 6 females) and 8 age-matched non-Parkinsonian older adults (5 females). Intermuscular coherence was analyzed between agonist-agonist and agonist-antagonist muscle pairs in the alpha (8-13 Hz) and beta (15-35 Hz) frequency bands. Results: CoP parameters increased from bipedal to unipedal stance in both groups (p < 0.01), but did not increase from the firm to compliant surface condition (p > 0.05). During unipedal stance, CoP path length was shorter in older adults with PD (2027.9 ± 1074.1 mm) compared to controls (3128.5 ± 1198.7 mm) (p < 0.01). Alpha and beta agonist-agonist and agonist-antagonist coherence increased by 28% from bipedal to unipedal stance (p > 0.05), but did not differ between older adults with PD (0.09 ± 0.07) and controls (0.08 ± 0.05) (p > 0.05). The older adults with PD also had greater normalized EMG amplitude of the LG (63.5 ± 31.7%) and TA (60.6 ± 38.4%) during the balance tasks (p > 0.05) than the non-Parkinsonian counterparts. Discussion: Older adults with PD had shorter path lengths during unipedal stance and required greater muscle activation than older adults without PD to perform the tasks, but intermuscular coherence did not differ between the groups. This may be attributable to their early disease stage and high motor function.

Hand movements influence the perception of time in a prediction motion task.

Human perception of time is far from accurate and is subject to distortions. Previous research has demonstrated that any manipulation that distorts the perceived velocity of visible moving objects may shift prediction motion (PM) performance during occlusion. However, it is not clear whether motor action has the same influence during occlusion in the PM task. This work evaluated the influence of action on PM performance in two experiments. In both cases, participants performed an interruption paradigm, evaluating if an occluded object had reappeared earlier or later than expected. This task was done simultaneously with a motor action. In Experiment 1, we compared the PM performance according to the timing of the action made while the object was still visible or occluded. In Experiment 2, participants had to perform (or not) a motor action if the target was green (or red). In both experiments, our results showed that the duration of the object's occlusion was underestimated in the specific case of acting during the occlusion period. These results suggest that action and temporal perception share similar neural bases. Future research is needed to confirm this hypothesis.

Increased intensity of unintended mirror muscle contractions after cervical spinal cord injury is associated with changes in interhemispheric and corticomuscular coherences.

Mirror contractions refer to unintended contractions of the contralateral homologous muscles during voluntary unilateral contractions or movements. Exaggerated mirror contractions have been found in several neurological diseases and indicate dysfunction or lesion of the cortico-spinal pathway. The present study investigates mirror contractions and the associated interhemispheric and corticomuscular interactions in adults with spinal cord injury (SCI) - who present a lesion of the cortico-spinal tract - compared to able-bodied participants (AB). Eight right-handed adults with chronic cervical SCI and ten age-matched right-handed able-bodied volunteers performed sets of right elbow extensions at 20% of maximal voluntary contraction. Electromyographic activity (EMG) of the right and left elbow extensors, interhemispheric coherence over cerebral sensorimotor regions evaluated by electroencephalography (EEG) and corticomuscular coherence between signals over the cerebral sensorimotor regions and each extensor were quantified. Overall, results revealed that participants with SCI exhibited (1) increased EMG activity of both active and unintended active limbs, suggesting more mirror contractions, (2) reduced corticomuscular coherence between signals over the left sensorimotor region and the right active limb and increased corticomuscular coherence between the right sensorimotor region and the left unintended active limb, (3) decreased interhemispheric coherence between signals over the two sensorimotor regions. The increased corticomuscular communication and decreased interhemispheric communication may reflect a reduced inhibition leading to increased communication with the unintended active limb, possibly resulting to exacerbated mirror contractions in SCI. Finally, mirror contractions could represent changes of neural and neuromuscular communication after SCI.

Untreated adolescent idiopathic scoliotic girls display altered balance modalities during self-paced voluntary body sways compared to able-bodied girls.

INTRODUCTION: This study investigated self-paced voluntary oscillations of scoliotic and non-scoliotic girls. Temporal variables and frequency coherence were calculated for the overall, low and high frequency bandwidths of the center of pressure excursions and free-moment to identify which variables best describe sway balance modalities in both groups. METHODS: Twenty-three girls with adolescent idiopathic moderate scoliosis (spinal curves to the right) formed the scoliotic group and 19 matched able-bodied girls formed the non-scoliotic group. Each girl performed self-paced voluntary medio-lateral and antero-posterior sways while standing on a force platform. Center of pressure displacements, out of plane deviation and free-moment were measured and their frequency content calculated. The magnitude of the coherence was calculated for each signal pairs for three frequency ranges. RESULTS: In both sway conditions, the center of pressure excursion parameters were on average 28% higher for the scoliotic group. Factor analysis revealed that balance modalities were essentially based on frequency coherence pair interactions whereas temporal parameters play a secondary role. However, these balance modalities were altered in the scoliotic group. They relied essentially on 2 additional principal components and 3 additional variables reflecting a fine tuning of the control mechanism to maintain dynamic balance. INTERPRETATION: Scoliotic girls appear to be performing a wide ellipsoidal trajectory when performing whole body oscillations. Superfluous variables could be related to the difficulty in preserving balance during body sway tasks and could parasitize the scoliotic dynamic control balance modalities. Self-paced voluntary sways could be an appropriate complementary balance test for untreated scoliotic girls.

Corticomuscular Coherence and Motor Control Adaptations after Isometric Maximal Strength Training.

Strength training (ST) induces corticomuscular adaptations leading to enhanced strength. ST alters the agonist and antagonist muscle activations, which changes the motor control, i.e., force production stability and accuracy. This study evaluated the alteration of corticomuscular communication and motor control through the quantification of corticomuscular coherence (CMC) and absolute (AE) and variable error (VE) of the force production throughout a 3 week Maximal Strength Training (MST) intervention specifically designed to strengthen ankle plantarflexion (PF). Evaluation sessions with electroencephalography, electromyography, and torque recordings were conducted pre-training, 1 week after the training initiation, then post-training. Training effect was evaluated over the maximal voluntary isometric contractions (MVIC), the submaximal torque production, AE and VE, muscle activation, and CMC changes during submaximal contractions at 20% of the initial and daily MVIC. MVIC increased significantly throughout the training completion. For submaximal contractions, agonist muscle activation decreased over time only for the initial torque level while antagonist muscle activation, AE, and VE decreased over time for each torque level. CMC remained unaltered by the MST. Our results revealed that neurophysiological adaptations are noticeable as soon as 1 week post-training. However, CMC remained unaltered by MST, suggesting that central motor adaptations may take longer to be translated into CMC alteration.

The Effects of Spinal Manipulation on Motor Unit Behavior.

Over recent years, a growing body of research has highlighted the neural plastic effects of spinal manipulation on the central nervous system. Recently, it has been shown that spinal manipulation improved outcomes, such as maximum voluntary force and limb joint position sense, reflecting improved sensorimotor integration and processing. This study aimed to further evaluate how spinal manipulation can alter neuromuscular activity. High density electromyography (HD sEMG) signals from the tibialis anterior were recorded and decomposed in order to study motor unit changes in 14 subjects following spinal manipulation or a passive movement control session in a crossover study design. Participants were asked to produce ankle dorsiflexion at two force levels, 5% and 10% of maximum voluntary contraction (MVC), following two different patterns of force production ("ramp" and "ramp and maintain"). A significant decrease in the conduction velocity (p = 0.01) was observed during the "ramp and maintain" condition at 5% MVC after spinal manipulation. A decrease in conduction velocity suggests that spinal manipulation alters motor unit recruitment patterns with an increased recruitment of lower threshold, lower twitch torque motor units.

Do Older People Accurately Estimate the Length of Their First Step during Gait Initiation?

Background/Study Context: Advancing age is associated with a decrease in step length. In line with previous studies showing that older adults often overestimate their motor abilities, we investigate whether older adults overestimate the length of their first step during gait initiation. The underlying effect could be a failure to update the internal model of motor action as a function of age-related motor decline. Methods: Without taking a step, community-dwelling older women (n = 22, age range: 68-87 years) and younger women (n = 19, age range: 19-33 years) estimated the length of their first step for both preferred step length and largest step length, which were performed without endangerment. Thereafter, the participants performed real gait initiation for both types of steps. The estimated step lengths were compared to the actual step lengths. Results: Older adults judged their first step as larger than it was (mean error: 30% for the preferred step and 9% for the largest step). A fine-grained analysis showed that this effect mainly concerned those for whom an increased risk of falling was suspected. These older adults were also among those who performed the shortest steps, and they presented with a slight decrease in cognitive functioning. Younger participants underestimated their preferred step length. Overall, the estimates were more accurate for the largest steps than for the preferred-length steps. Conclusion: Step length estimation revealed powerful evidence for overestimation in older adults. Those who overestimated step length presented with more signs of motor decline. While this result sustains the idea of an insufficient actualization of the motor-action model, the explanation also refers to more global appraisal processes. Further research should explore the relevance of this task as a clinical laboratory tool for assessing gait capacity and the risk of falling.

Frequency coherence analysis of postural balance in able-bodied and in non-treated adolescent idiopathic scoliotic girls.

BACKGROUND: This study test if the frequency coherence calculated for the overall, low and high frequency bandwidths of the center of pressure excursions and free-moment calculated during standing balance are similar between scoliotic and non-scoliotic girls and if the coherence values within each frequency band are comparable for a given group of girls. METHODS: Twenty-nine girls with adolescent idiopathic scoliosis formed the scoliotic group and 22 able-bodied girls formed the non-scoliotic group. Each girl maintained a quiet upright stance on a force plate. Three trials were performed at a sampling frequency of 64 Hz for 64 s. Mean anterio-posterior, medio-lateral center of pressure positions and free-moment were measured and their frequency content calculated. The magnitude of the coherence was calculated for each signal pairs for three frequency ranges. RESULTS: The magnitude of the medio-lateral center of pressure/free-moment coherence in the low and high frequency bands was significantly different between the groups. Within each group, the magnitude of the medio-lateral center of pressure/free-moment coherence was significantly higher than the other two coherence pairs at low frequencies (P < 0.001). Factor analysis revealed that able-bodied girls exhibited a mixed standing balance modality consisting of posture (center of pressure) and proprioceptive information (free-moment). Scoliotic girls adopted an adaptive modality mostly based on proprioception information to maintain their standing balance. INTERPRETATION: Scoliotic girls systematically depend on the free-moment to modulate their antero-posterior center of pressure displacements. These results suggest a postural reeducation program aimed at improving proprioception while repositioning the mean center of pressure by postural corrections.

Investigation of Optimal Afferent Feedback Modality for Inducing Neural Plasticity with A Self-Paced Brain-Computer Interface.

Brain-computer interfaces (BCIs) can be used to induce neural plasticity in the human nervous system by pairing motor cortical activity with relevant afferent feedback, which can be used in neurorehabilitation. The aim of this study was to identify the optimal type or combination of afferent feedback modalities to increase cortical excitability in a BCI training intervention. In three experimental sessions, 12 healthy participants imagined a dorsiflexion that was decoded by a BCI which activated relevant afferent feedback: (1) electrical nerve stimulation (ES) (peroneal nerve-innervating tibialis anterior), (2) passive movement (PM) of the ankle joint, or (3) combined electrical stimulation and passive movement (Comb). The cortical excitability was assessed with transcranial magnetic stimulation determining motor evoked potentials (MEPs) in tibialis anterior before, immediately after and 30 min after the BCI training. Linear mixed regression models were used to assess the changes in MEPs. The three interventions led to a significant (p < 0.05) increase in MEP amplitudes immediately and 30 min after the training. The effect sizes of Comb paradigm were larger than ES and PM, although, these differences were not statistically significant (p > 0.05). These results indicate that the timing of movement imagery and afferent feedback is the main determinant of induced cortical plasticity whereas the specific type of feedback has a moderate impact. These findings can be important for the translation of such a BCI protocol to the clinical practice where by combining the BCI with the already available equipment cortical plasticity can be effectively induced. The findings in the current study need to be validated in stroke populations.

Effect of the phase of force production on corticomuscular coherence with agonist and antagonist muscles.

During isometric contractions, the net joint torque stability is modulated with the force production phases, i.e., increasing (IFP), holding (HFP), and decreasing force (DFP) phases. It was hypothesized that this modulation results from an altered cortical control of agonist and antagonist muscle activations. Eleven healthy participants performed 50 submaximal isometric ankle plantar flexion contractions. The force production phase effect (IFP, HFP and DFP) was assessed on the net joint torque stability, agonist and antagonist muscles activations, cortical activation, and corticomuscular coherence (CMC) with agonist and antagonist muscles. In comparison to HFP, the net joint torque stability, the agonist muscles activation and the CMC with agonist muscles were lower during IFP and even more during DFP. Antagonist muscle activations, cortical activations and CMC with antagonist muscles were higher during HFP than during IFP only. Increased CMC with agonist and antagonist muscles appeared to enhance the fine motor control. At a cortical level, agonist and antagonist muscle activations seemed to be controlled independently according to their muscle function and the phase of force production. Results revealed that CMC was an adequate measure to investigate the cortical regulation of agonist and antagonist muscle activations. This may have potential applications for patients with altered muscle activations.

Effect of training status on beta-range corticomuscular coherence in agonist vs. antagonist muscles during isometric knee contractions.

Antagonist muscle co-activation is thought to be partially regulated by cortical influences, but direct motor cortex involvement is not fully understood. Corticomuscular coherence (CMC) measures direct functional coupling of the motor cortex and muscles. As antagonist co-activation differs according to training status, comparison of CMC in agonist and antagonist muscles and in strength-trained and endurance-trained individuals may provide in-depth knowledge of cortical implication in antagonist muscle co-activation. Electroencephalographic and electromyographic signals were recorded, while 10 strength-trained and 11 endurance-trained participants performed isometric knee contractions in flexion and extension at various torque levels. CMC magnitude in 13-21 and 21-31 Hz frequency bands was quantified by CMC analysis between Cz electroencephalographic electrode activity and all electromyographic signals. CMC was significant in both 13-21 and 21-31 Hz frequency bands in flexor and extensor muscles regardless of participant group, torque level, and direction of contraction. CMC magnitude decreased more in antagonist than in agonist muscles as torque level increased. Finally, CMC magnitude was higher in strength-trained than in endurance-trained participants. These findings provide experimental evidence that the motor cortex directly regulates both agonist and antagonist muscles. Nevertheless, the mechanisms underlying muscle activation may be specific to their function. Between-group modulation of corticomuscular coherence may result from training-induced adaptation, re-emphasizing that corticomuscular coherence analysis may be efficient in characterizing corticospinal adaptations after long-term muscle specialization.

Impaired corticomuscular coherence during isometric elbow flexion contractions in humans with cervical spinal cord injury.

After spinal cord injury (SCI), the reorganization of the neuromuscular system leads to increased antagonist muscles' co-activation-that is, increased antagonist vs. agonist muscles activation ratio-during voluntary contractions. Increased muscle co-activation is supposed to result from reduced cortical influences on spinal mechanisms inhibiting antagonist muscles. The assessment of the residual interactions between cortical and muscles activity with corticomuscular coherence (CMC) in participants with SCI producing different force levels may shed new lights on the regulation of muscle co-activation. To achieve this aim, we compared the net joint torque, the muscle co-activation and the CMC ~ 10 and ~ 20 Hz with both agonist and antagonist muscles in participants with SCI and healthy participants performing actual isometric elbow flexion contractions at three force levels. For all participants, overall CMC and muscle co-activation decreased with the increase in the net joint torque, but only CMC ~ 10 Hz was correlated with muscle co-activation. Participants with SCI had greater muscle co-activation and lower CMC ~ 10 Hz, at the highest force levels. These results emphasize the importance of CMC as a mechanism that could take part in the modulation of muscle co-activation to maintain a specific force level. Lower CMC ~ 10 Hz in SCI participants may reflect the decreased cortical influence on spinal mechanisms, leading to increased muscle co-activation, although plasticity of the corticomuscular coupling seems to be preserved after SCI to modulate the force level. Clinically, the CMC may efficiently evaluate the residual integrity of the neuromuscular system after SCI and the effects of rehabilitation.

Quantification of Movement-Related EEG Correlates Associated with Motor Training: A Study on Movement-Related Cortical Potentials and Sensorimotor Rhythms.

The ability to learn motor tasks is important in both healthy and pathological conditions. Measurement tools commonly used to quantify the neurophysiological changes associated with motor training such as transcranial magnetic stimulation and functional magnetic resonance imaging pose some challenges, including safety concerns, utility, and cost. EEG offers an attractive alternative as a quantification tool. Different EEG phenomena, movement-related cortical potentials (MRCPs) and sensorimotor rhythms (event-related desynchronization-ERD, and event-related synchronization-ERS), have been shown to change with motor training, but conflicting results have been reported. The aim of this study was to investigate how the EEG correlates (MRCP and ERD/ERS) from the motor cortex are modulated by short (single session in 14 subjects) and long (six sessions in 18 subjects) motor training. Ninety palmar grasps were performed before and after 1 × 45 (or 6 × 45) min of motor training with the non-dominant hand (laparoscopic surgery simulation). Four channels of EEG were recorded continuously during the experiments. The MRCP and ERD/ERS from the alpha/mu and beta bands were calculated and compared before and after the training. An increase in the MRCP amplitude was observed after a single session of training, and a decrease was observed after six sessions. For the ERD/ERS analysis, a significant change was observed only after the single training session in the beta ERD. In conclusion, the MRCP and ERD change as a result of motor training, but they are subject to a marked intra- and inter-subject variability.

I can't reach it! Focus on theta sensorimotor rhythm toward a better understanding of impaired action-perception coupling.

It is known that anxiety (ANX) impairs action-perception coupling. This study tests whether this impairment could be associated with an alteration of the sensorimotor function. To this aim, the cortical activities underlying the sensorimotor function were recorded in twelve volunteers in a reach-to-grasp paradigm, in which the level of ANX and the position of a glass were manipulated. The experimental manipulation of the ANX-related somatosensory state was expected to prompt participants to underestimate their reaching-to-grasp capabilities while the sensorimotor-related oscillatory brain activities around the 6-Hz (θ) frequency over motor-related and parietal regions were expected to be modulated. We also investigated the oscillatory brain dynamics around the 11.5-Hz (fast-α) frequency as a neural hallmark of ANX manipulation induced by the breath-restriction. Results indeed showed that participants underestimated their reaching-to-grasp maximal performance. Concomittantly, θ-EEG synchronization over the motor cortex contralateral to the dominant hand was higher during glass presentation under breath-restriction condition (+20.1%; p<0.05), and when the glass was perceived as non-reachable (+20.0%; p<0.05). Fast-α-EEG desynchronization was reduced under breath-restriction (-37.7%; p<0.05). The results confirm that ANX-related impairment of action-perception coupling co-modulates with theta-sensorimotor rhythm. This finding is discussed as an altered "readiness state" in the reaching-related cortical network, while individuals are anxious.

Increased antagonist muscle activity in cervical SCI patients suggests altered reciprocal inhibition during elbow contractions.

OBJECTIVE: After spinal cord injury (SCI), the antagonist muscles activation is increased during voluntary contractions and reflex conditioning protocols. This increase can be the result of both muscle atrophy and reciprocal facilitation mechanism. It remains however unclear to what extent increased antagonist muscles activation could be rather attributable to central vs. peripheral changes during voluntary contractions achieved by SCI participants. METHODS: We investigated the activations of elbow extensors and flexors during isometric elbow flexion and extension contractions performed at 3 force levels by 10 healthy participants and 8 participants with cervical SCI (cSCI). RESULTS: At similar force level and absolute net torque in flexion, the antagonist muscles activation was increased for the participants with cSCI. At similar absolute net torque in extension, the activations of agonist and antagonist muscles were increased for the participants with cSCI. CONCLUSION: During flexion contractions, increased antagonist muscles activation may be explained by extensors atrophy or reciprocal facilitation. During extension contractions, increased antagonist muscles activation may reflect the importance of reciprocal facilitation as antagonist muscles were evaluated as intact by clinical testing and maximal net joint torque recording. SIGNIFICANCE: These results in cSCI participants revealed an increased activation of antagonist muscles, which may reflect a reorganization of the spinal reflexes and their supraspinal control involved during isometric elbow contractions.

An enhanced experimental procedure to rationalize on the impairment of perception of action capabilities.

It is well documented that changes in the physiological states of the perceiver-actor influence the perception of action capabilities. However, because experimental procedures of most studies involved a limitless availability for stimuli visual encoding and perceptual strategies, it remains difficult to adopt a single position among the large range of alternative interpretations for impaired perception. A reaching-to-grasp paradigm under breathing restriction was adapted from Graydon et al. (Cogn Emot 26:1301-1305, 2012) to standardize the time for encoding of stimuli information and narrowed the involvement of perceptual strategies. In the present study, we propose a highly controlled environment where the discrete information is presented during 300 ms, congruently with neurophysiological studies focused on visuomotor transformation. An underestimation of the perception of action capabilities is found under breath restriction, suggesting that 300 ms for stimuli encoding is sufficient to induce altered visuomotor brain transformations when limiting the involvement of perceptual strategies. This result suggests that such behavior could refer to an impaired brain potentiation of the perceptual occurrence, providing strong hypotheses on the brain dynamics of sensorimotor integration that underlie impaired perception of action capabilities in stressful situations.

Motor-related cortical activity after cervical spinal cord injury: multifaceted EEG analysis of isometric elbow flexion contractions.

Electroencephalographic (EEG) studies have well established that motor cortex (M1) activity ~20 Hz decreases during muscular contraction and increases as soon as contraction stops, which are known as event-related desynchronization (ERD) and event-related synchronization (ERS), respectively. ERD is supposed to reflect M1 activation, sending information to recruited muscles, while the process underlying ERS is interpreted either as active cortical inhibition or as processing of sensory inputs. Investigation of the process behind ERD/ERS in people with spinal cord injury (SCI) would be particularly relevant since their M1 remains effective despite decreased sensorimotor abilities. In this study, we recorded net joint torque and EEG in 6 participants with cervical SCI and 8 healthy participants who performed isometric elbow flexion at 3 force levels. Multifaceted EEG analysis was introduced to assess ERD/ERS according to their amplitude, frequency range and duration. The results revealed that net joint torque increased with the required force level for all participants and time to contraction inhibition was longer in the SCI group. At the cortical level, ERD/ERS frequency ranges increased with the required force level in all participants, indicating that the modulation of cortical activity with force level is preserved after SCI. However, ERS amplitude decreased only in SCI participants, which may be linked to delayed contraction inhibition. All in all, cortical modulation of frequency range and amplitude could reflect two different kinds of neural communication.

Does the force level modulate the cortical activity during isometric contractions after a cervical spinal cord injury?

OBJECTIVE: This study investigated the effects of a cervical spinal cord injury (SCI) on the modulation of cortical desynchronization (ERD) during isometric contractions at different force levels. METHODS: For 8 able-bodied (AB) and 6 cervical SCI participants, the net joint moment and electroencephalographic activities were recorded during isometric contractions of the right elbow in flexion and in extension at 3 force levels, that is, during intact and altered muscle contractions for SCI participants. The mean net moment and ∼20 Hz ERD from C3 electroencephalographic electrode were compared between AB and SCI participants. RESULTS: In flexion, that is, during intact contractions for all participants, the mean net moment and the ERD increased with the required force level. In extension, that is, during altered contractions, the mean net moment increased for 3 SCI participants while it was almost zero for 3 other SCI participants. The associated ERD increased with the required force level for all participants. CONCLUSION: The cortical desynchronization was modulated by the intent to modulate the force level rather than the actual modulation of the force production. SIGNIFICANCE: These results provide a better understanding of the modulation of the cortical desynchronization following SCI. Potential applications could include the control of neuroprostheses.