Differential neural mechanisms for movement adaptations following neuromuscular training in young female athletes with a history of sports-related concussion.

Sports-related concussion (SRC) in adolescent athletes is associated with an increased risk of subsequent lower extremity injury. Neuromuscular training (NMT) has shown promise for reducing lower extremity injuries following SRC, however, neural adaptations in response to changes in lower extremity biomechanics following NMT in athletes with a history of SRC (HxSRC) remains poorly understood. Therefore, the purpose of this study was to identify changes in neural activity associated with lower extremity movement adaptations following a six-week NMT intervention in athletes with a HxSRC. Thirty-two right-hand/foot-dominant female adolescent athletes (16 with self-reported HxSRC, 16 age- and anthropometrically-matched controls) completed a bilateral leg press task with 3D motion analysis during functional magnetic resonance imaging (fMRI). Movement adaptations were defined as a change in frontal and sagittal plane range of motion (ROM) during the fMRI bilateral leg press task. Significant pre- to post-NMT reductions were observed in the non-dominant (left) mean frontal plane ROM. Whole-brain neural correlate analysis revealed that increased cerebellar activity was significantly associated with reduced mean left-knee frontal ROM for matched controls. Exploratory within group analyses identified neural correlates in the postcentral gyrus for the HxSRC group which was associated with reduced mean left-knee frontal plane ROM. These distinct longitudinal changes provide preliminary evidence of differential neural activity associated with NMT to support knee frontal plane control in athletes with and without a HxSRC.

Implicit audiomotor adaptation.

Sensorimotor adaptation alters mappings between motor commands and their predicted outcomes. Such remapping has been extensively studied in the visual domain, but the degree to which it occurs in modalities other than vision remains less well understood. Here, we manipulated the modality of reach target presentation to compare sensorimotor adaptation in response to perturbations of visual and auditory feedback location. We compared the extent of adaptation to perturbed sensory feedback for visual and auditory sensory modalities, and the magnitude of reach-direction aftereffects when the perturbation was removed. To isolate the contribution of implicit sensorimotor recalibration to adaptation in reach direction, we held sensory prediction errors and task-performance errors constant via a task-irrelevant clamp of sensory feedback. Seventy-two participants performed one of three experiments in which target location information and endpoint reach direction feedback were presented by loudspeakers (n = 24), headphones (n = 24), or a visual display (n = 24). Presentation durations for target stimuli (500 ms) and (non-veridical) endpoint feedback of reach direction (100 ms) were matched for visual and auditory modalities. For all three groups, when endpoint feedback was perturbed, adaptation was evident: reach-directions increased significantly in the direction opposite the clamped feedback, and a significant aftereffect persisted after participants were instructed that the perturbation had been removed. This study provides new evidence that implicit sensorimotor adaptation occurs in response to perturbed auditory feedback of reach direction, suggesting that an implicit neural process to recalibrate sensory to motor maps in response to sensory prediction errors may be ubiquitous across sensory modalities.

The cerebellum computes frequency dynamics for motions with numerical precision and cross-individual uniformity.

Cross-individual variability is considered the essence of biology, preventing precise mathematical descriptions of biological motion1-7 like the physics law of motion. Here we report that the cerebellum shapes motor kinematics by encoding dynamic motor frequencies with remarkable numerical precision and cross-individual uniformity. Using in-vivo electrophysiology and optogenetics in mice, we confirmed that deep cerebellar neurons encoded frequencies via populational tuning of neuronal firing probabilities, creating cerebellar oscillations and motions with matched frequencies. The mechanism was consistently presented in self-generated rhythmic and non-rhythmic motions triggered by a vibrational platform, or skilled tongue movements of licking in all tested mice with cross-individual uniformity. The precision and uniformity allowed us to engineer complex motor kinematics with designed frequencies. We further validated the frequency-coding function of the human cerebellum using cerebellar electroencephalography recordings and alternating-current stimulation during voluntary tapping tasks. Our findings reveal a cerebellar algorithm for motor kinematics with precision and uniformity, the mathematical foundation for brain-computer interface for motor control.

A task-dependent analysis of closed vs. open and fine vs. gross motor skills in handedness.

The traditional classifications of motor skills nature (open vs closed; fine vs gross) have not been considered in handedness investigations. Instead, previous research focused on comparing complex vs less complex motor behaviour, leaving a gap in the literature. We compared manual preference between different motor skill characteristics, namely: fine and closed (FC), gross and closed (GC) and gross and open (GO) tasks. The hand preference was assessed with the Global Lateral Preference Inventory in four hundred and forty participants (244 women) aged from 18 to 59 years old. By assessing the degree and direction of handedness in different motor skills, our results showed a stronger lateralization pattern for FC motor skills as compared to GC and GO, with GO also being less lateralized than GC. Our results expand those of previous investigations that used the motor skill complexity definitions by showing how handedness can also be modulated by the interaction between classic motor skills classifications. Future research should consider fine vs. gross and open vs. closed classifications when selecting tasks for analysis of asymmetries of preference.

Sustained submaximal isometric wrist flexion and wrist extension contractions uniquely impair maximal voluntary contraction force in the antagonist wrist action.

When fatigued, the wrist extensors, which are the primary wrist stabilizers, impair distal upper limb motor performance in a surprisingly similar way as when fatiguing the wrist flexors. It is possible that the wrist extensors are so active as antagonists that they develop an equal degree of fatigue during wrist flexion contractions, making it difficult to truly isolate their impact on performance. Thus, the purpose of this study was to examine how wrist flexion/extension forces are impaired following either agonist or antagonist sustained submaximal wrist contractions. 13 male participants attended four laboratory sessions. In these sessions, fatigue was induced via a sustained submaximal isometric contraction of either wrist flexion or extension. These contractions were held for up to 10 min at 20% of the participant's baseline maximal voluntary contraction (MVC) force. Throughout the sustained contraction, intermittent agonist (matching the sustained contraction) or antagonist (opposing the sustained contraction) MVCs were performed. Unsurprisingly, agonist MVC forces decreased significantly more than antagonist (Agonist: 58.5%, Antagonist: 86.5% of MVC, P < 0.001). However, while there were no differences in antagonist wrist extension and flexion MVC decreases (Wrist Flexion: 87.5%, Wrist Extension: 85.5%, P = 0.41), wrist extension MVCs did decrease significantly more than wrist flexion MVCs when forces were expressed relative to the agonist (P = 0.036). These findings partially support the hypothesis that the wrist extensors may be more susceptible to developing fatigue when functioning as antagonists than the wrist flexors. This work will help equip future research into the motor control of the upper limb and the prevention of forearm-related musculoskeletal disorders.

Regular cannabis use modulates gamma activity in brain regions serving motor control.

BACKGROUND: People who regularly use cannabis exhibit altered brain dynamics during cognitive control tasks, though the impact of regular cannabis use on the neural dynamics serving motor control remains less understood. AIMS: We sought to investigate how regular cannabis use modulates the neural dynamics serving motor control. METHODS: Thirty-four people who regularly use cannabis (cannabis+) and 33 nonusers (cannabis-) underwent structured interviews about their substance use history and performed the Eriksen flanker task to map the neural dynamics serving motor control during high-density magnetoencephalography (MEG). The resulting neural data were transformed into the time-frequency domain to examine oscillatory activity and were imaged using a beamforming approach. RESULTS: MEG sensor-level analyses revealed robust beta (16-24 Hz) and gamma oscillations (66-74 Hz) during motor planning and execution, which were imaged using a beamformer. Both responses peaked in the left primary motor cortex and voxel time series were extracted to evaluate the spontaneous and oscillatory dynamics. Our key findings indicated that the cannabis+ group exhibited weaker spontaneous gamma activity in the left primary motor cortex relative to the cannabis- group, which scaled with cannabis use and behavioral metrics. Interestingly, regular cannabis use was not associated with differences in oscillatory beta and gamma activity, and there were no group differences in spontaneous beta activity. CONCLUSIONS: Our findings suggest that regular cannabis use is associated with suppressed spontaneous gamma activity in the left primary motor cortex, which scales with the degree of cannabis use disorder symptomatology and is coupled to behavioral task performance.

One side effect: two networks? Lateral and posteromedial stimulation spreads induce dysarthria in subthalamic deep brain stimulation for Parkinson's disease.

BACKGROUND: Stimulation-induced dysarthria (SID) is a troublesome and potentially therapy-limiting side effect of deep brain stimulation of the subthalamic nucleus (STN-DBS) in patients with Parkinson's disease (PD). To date, the origin of SID, and especially whether there is an involvement of cerebellar pathways as well as the pyramidal tract, remains a matter of debate. Therefore, this study aims to shed light on structural networks associated with SID and to derive a data-driven model to predict SID in patients with PD and STN-DBS. METHODS: Randomised, double-blinded monopolar reviews determining SID thresholds were conducted in 25 patients with PD and STN-DBS. A fibre-based mapping approach, implementing the calculation of fibr-wise ORs for SID, was employed to identify the distributional pattern of SID in the STN's vicinity. The ability of the data-driven model to classify stimulation volumes as 'causing SID' or 'not causing SID' was validated by calculating receiver operating characteristics (ROC) in an independent out-of-sample cohort comprising 14 patients with PD and STN-DBS. RESULTS: Local fibre-based stimulation maps showed an involvement of fibres running lateral and posteromedial to the STN in the pathogenesis of SID, independent of the investigated hemisphere. ROC analysis in the independent out-of-sample cohort resulted in a good fit of the data-driven model for both hemispheres (area under the curve (AUC)left=0.88, AUCright=0.88). CONCLUSIONS: This study reveals an involvement of both, cerebello-thalamic fibres, as well as the pyramidal tract, in the pathogenesis of SID in STN-DBS. The results may impact future postoperative programming strategies to avoid SID in patients with PD and STN-DBS TRIAL REGISTRATION NUMBER: DRKS00023221; German Clinical Trials Register (DRKS) Number.

Reference measures of lower-limb joint range of motion, muscle strength, and selective voluntary motor control of typically developing children aged 5-17 years.

Background: Joint range of motion based on the neutral null method, muscle strength based on manual muscle testing, and selective voluntary motor control based on selective control assessment of the lower extremity are standard parameters of a pediatric three-dimensional clinical gait analysis. Lower-limb reference data of children are necessary to identify and quantify abnormalities, but these are limited and when present restricted to specific joints or muscles. Methods: This is the first study that encompasses the aforementioned parameters from a single group of 34 typically developing children aged 5-17 years. Left and right values were averaged for each participant, and then the mean and standard deviation calculated for the entire sample. The data set was tested for statistical significance (p < 0.05). Results: Joint angle reference values are mostly consistent with previously published standards, although there is a large variability in the existing literature. All muscle strength distributions, except for M. quadriceps femoris, differ significantly from the maximum value of 5. The mean number of repetitions of heel-rise test is 12 ± 5. Selective voluntary motor control shows that all distributions, except for M. quadriceps femoris, differ significantly from the maximum value of 2. Conclusion: Since typically developing children do not match expectations and reference values from the available literature and clinical use, this study emphasizes the importance of normative data. Excessively high expectations lead to typically developing children being falsely underestimated and affected children being rated too low. This is of great relevance for therapists and clinicians. Level of evidence: 3.

Utilizing Entropy of Cadence to Optimize Cycling Rehabilitation in Individuals With Parkinson's Disease.

BACKGROUND: Previous studies have established that increased Sample Entropy (SampEn) of cadence, a measure of non-linear variability, during dynamic cycling leads to greater improvements in motor function for individuals with Parkinson's disease (PD). However, there is significant variability in responses among individuals with PD due to symptoms and disease progression. OBJECTIVES: The aim of this study was to develop and test a paradigm for adapting a cycling exercise intervention using SampEn of cadence and rider effort to improve motor function. METHODS: Twenty-two participants were randomized into either patient-specific adaptive dynamic cycling (PSADC) or non-adaptive (NA) group. SampEn of cadence was calculated after each of the 12 sessions, and motor function was evaluated using the Kinesia test. Pearson's correlation coefficient was used to analyze the relationship between SampEn of cadence and motor function improvement. Multiple linear regression (MLR) was used to identify the strongest predictors of motor function improvement. RESULTS: Pearson's correlation coefficient revealed a significant correlation between SampEn of cadence and motor function improvements (R2 = -.545, P = .009), suggesting that higher SampEn of cadence led to greater motor function improvement. MLR demonstrated that SampEn of cadence was the strongest predictor of motor function improvement (ß = -8.923, t = -2.632, P = .018) over the BMI, Levodopa equivalent daily dose, and effort. CONCLUSIONS: The findings show that PSADC paradigm promoted a greater improvement in motor function than NA dynamic cycling. These data will be used to develop a predictive model to optimize motor function improvement after cycling in individuals with PD.

Interlimb transfer of sequential motor learning between upper and lower effectors.

BACKGROUND: Interlimb transfer of sequential motor learning (SML) refers to the positive influence of prior experiences in performing the same sequential movements using different effectors. Despite evidence from intermanual SML, and while most daily living activities involve interlimb cooperation and coordination between the four limbs, nothing is known about bilateral SML transfer between the upper and lower limbs. RESEARCH QUESTION: We examined the transfer of bilateral SML from the upper to the lower limbs and vice versa. METHODS: Twenty-four participants had to learn an initial bilateral SML task using the upper limbs and then performed the same sequence using the lower limbs during a transfer SML task. They performed the reversed situation 1 month apart. The performance was evaluated at the beginning and the end of both initial and transfer SML practice phases. RESULTS: Significant and reciprocal transfer gains in performance were observed regardless of the effectors. Greater transfer gains in performance were observed at the beginning of the transfer SML from the lower to the upper limbs (44 %) but these gains vanished after practice with the transfer effectors (5 %). Although smaller gains were initially achieved in the transfer of SML from the upper to the lower limbs (15 %), these gains persisted and remained significant (9 %) after practice with the transfer effectors. SIGNIFICANCE: Our results provide evidence of a reciprocal and asymmetrical interlimb transfer of bilateral SML between the upper and lower limbs. These findings could be leveraged as a relevant strategy in the context of sports and functional rehabilitation.

The Kinematics of 3D Arm Movements in Sub-Acute Stroke: Impaired Inter-Joint Coordination is Attributable to Both Weakness and Flexor Synergy Intrusion.

BACKGROUND: It has long been of interest to characterize the components of the motor abnormality in the arm after stroke. One approach has been to decompose the hemiparesis phenotype into negative signs, such as weakness, and positive signs, such as intrusion of synergies. We sought to identify the contributions of weakness and flexor synergy to motor deficits in sub-acute stroke. METHODS: Thirty-three sub-acute post-stroke participants and 16 healthy controls performed two functional arm movements; one within flexor synergy (shoulder and elbow flexion), and the other outside flexor synergy (shoulder flexion and elbow extension). We analyzed upper limb 3D kinematics to assess both overall task performance and intrusion of pathological synergies. Weakness and spasticity were also measured. RESULTS: Both tasks produced similar impairments compared to controls. Analysis of elbow and shoulder multi-joint coordination patterns revealed intrusion of synergies in the out-of-synergy reaching task based on the time spent within a flexion-flexion pattern and the correlation between shoulder and elbow angles. Regression analysis indicated that both weakness and synergy intrusion contributed to motor impairment in the out-of-synergy reaching task. Notably, the Fugl-Meyer Assessment (FMA) was abnormal even when only weakness caused the impairment, cautioning that it is not a pure synergy scale. CONCLUSIONS: Weakness and synergy intrusion contribute to motor deficits in the sub-acute post-stroke period. An abnormal FMA score cannot be assumed to be due to synergy intrusion. Careful kinematic analysis of naturalistic movements is required to better characterize the contribution of negative and positive signs to upper limb impairment after stroke.

Investigation of adaptive muscle synergy modulated motor responses to grasping perturbations.

This study investigated how muscle synergies adapt in response to unexpected changes in object weight during lifting tasks. The aim was to discover which motor control strategies individuals use to maintain their grasping performance. Muscle synergies were extracted from the muscle activity of fifteen healthy participants who lifted objects of identical appearance but varying weights in a randomized order, which introduced artificial perturbations. Reaching and manipulation phases of object lifting were analyzed using constrained non-negative matrix factorization and k-means clustering. Participants exhibited a perturbation-independent and thus consistent recruitment of spatial synergy components, while significant adaptations in muscle synergy activation occurred in response to unexpected perturbations. Perturbations caused by unexpectedly heavy objects led to delayed and gradual increases in muscle synergy activation until the force required to lift the object was reached. In contrast, perturbations caused by lighter objects led to reductions in excess muscle synergy activation occurring later. Sensorimotor control maintains the modularity of muscle synergies. Even when external mechanical perturbations occur, the grasping performance is preserved, and control is adapted solely through muscle synergy activation. These results suggest that using pure spatial synergy components as control signals for myoelectric arm prostheses may prevent them from malfunctioning due to external perturbations.

Increased vowel contrast and intelligibility in connected speech induced by sensorimotor adaptation.

Alterations to sensory feedback can drive robust adaptive changes to the production of consonants and vowels, but these changes often have no behavioral relevance or benefit to communication (e.g., making "head" more like "had"). This work aims to align the outcomes of adaptation with changes known to increase speech intelligibility - specifically, adaptations that increase the acoustic contrast between vowels in running speech. To this end, we implemented a vowel centralization feedback perturbation paradigm that pushes all vowels towards the center of vowel space, making them sound less distinct from one another. Speakers across the adult lifespan adapted to the centralization perturbation during sentence production, increasing the global acoustic contrast among vowels and the articulatory excursions for individual vowels. These changes persisted after the perturbation was removed, including after a silent delay, and showed robust transfer to words that were not present in the sentences. Control analyses demonstrated that these effects were unlikely to be due to explicit pronunciation strategies and occurred in the face of increasingly more rapid and less distinct production of familiar sentences. Finally, sentence transcription by crowd-sourced listeners showed that speakers' vowel contrast predicted their baseline intelligibility and that experimentally-induced increases in contrast predicted intelligibility gains. These findings establish the validity of a sensorimotor adaptation paradigm to implicitly increase vowel contrast and intelligibility in connected speech, an outcome that has the potential to enhance rehabilitation in individuals who present with a reduced vowel space due to motor speech disorders, such as the hypokinetic dysarthria associated with Parkinson's disease.

Major Alteration Of Motor Control During Rem Sleep In Mice Models Of Sleep Disorders.

Alteration of motor control during REM sleep has been extensively described in sleep disorders, in particular in isolated REM sleep behavior disorder (iRBD) and narcolepsy type 1 (NT1). NT1 is caused by the loss of orexin/hypocretin (ORX) neurons. Unlike in iRBD, the RBD comorbid symptoms of NT1 is not associated with alpha-synucleinopathies. To determine whether the chronic absence of ORX neuropeptides is sufficient to induce RBD symptoms, we analyzed during REM sleep the EMG signal of the prepro-hypocretin knockout mice (ORX-/-), a recognized mouse model of NT1. Then, we evaluated the severity of motor alterations by comparing EMG data of ORX-/- mice to those of mice with a targeted suppression of the sublaterodorsal glutamatergic neurotransmission, a recognized rodent model of iRBD. We found a significant alteration of tonic and phasic components of EMG during REM sleep in ORX-/- mice, with more phasic events and more REM sleep episodes without atonia compared to the control wild-type mice. However, these phasic events were fewer, shorter and less complex in ORX-/- mice compared to the RBD-like ORX-/- mice. We thus show that ORX-deficiency, as seen in NT1, is sufficient to impair muscle atonia during REM sleep with a moderate severity of alteration as compared to isolated RBD mice. As described in NT1 patients, we report a major inter-individual variability in the severity and the frequency of RBD symptoms in ORX-deficient mice.

Drive away neck pain: Transformative motor control therapeutic neck exercises and tailored programs redefine posture for automotive workers.

BACKGROUND: Neck discomfort, arising from strained muscles, poor posture, accidents, or underlying medical conditions, significantly impacts daily activities and overall well-being, presenting a substantial healthcare challenge. OBJECTIVE: This study aims to evaluate the efficacy of motor control therapeutic neck exercise and a Structured Exercise Program on neck pain and posture among automobile industrial workers. METHODS: Using a lottery technique, 106 participants aged 20 to 45 were selected from the vicinity of Chennai's auto industries based on predetermined eligibility and exclusion criteria. Subsequently, participants were randomly assigned to either the motor control therapeutic neck exercise group or the structured exercise program group, each comprising 53 individuals. Participants received a comprehensive overview of the study and respective interventions, and their informed consent was obtained. Demographic details, Neck Injury and Disability scores, and Assessment of Postural and Ergonomic Characteristics data were then collected. RESULTS: Statistical analysis revealed a significant difference between the groups, with the Motor Control Therapeutic Neck Exercise group demonstrating superior outcomes in reducing pain and improving posture, with p-values less than 0.001. CONCLUSIONS: This study highlights the efficacy of Motor Control Therapeutic Neck Exercise over Structured Exercise in improving neck pain and posture among automobile industrial workers. These findings contribute valuable insights for the development of targeted interventions in occupational health settings.

Altered brain function during movement programming is linked with motor deficits after stroke: a high temporal resolution study.

Introduction: Stroke leads to motor deficits, requiring rehabilitation therapy that targets mechanisms underlying movement generation. Cortical activity during the planning and execution of motor tasks can be studied using EEG, particularly via the Event Related Desynchronization (ERD). ERD is altered by stroke in a manner that varies with extent of motor deficits. Despite this consensus in the literature, defining precisely the temporality of these alterations during movement preparation and performance may be helpful to better understand motor system pathophysiology and might also inform development of novel therapies that benefit from temporal resolution. Methods: Patients with chronic hemiparetic post-stroke (n = 27; age 59 ± 14 years) and age-matched healthy right-handed control subjects (n = 23; 59 ± 12 years) were included. They performed a shoulder rotation task following the onset of a stimulus. Cortical activity was recorded using a 256-electrode EEG cap. ERD was calculated in the beta frequency band (15-30 Hz) in ipsilesional sensorimotor cortex, contralateral to movement. The ERD was compared over time between stroke and control subjects using permutation tests. The correlation between upper extremity motor deficits (assessed by the Fugl-Meyer scale) and ERD over time was studied in stroke patients using Spearman and permutation tests. Results: Patients with stroke showed on average less beta ERD amplitude than control subjects in the time window of -350 to 50 ms relative to movement onset (t(46) = 2.8, p = 0.007, Cohen's d = 0.31, 95% CI [0.22: 1.40]). Beta-ERD values correlated negatively with the Fugl-Meyer score during the time window -200 to 400 ms relative to movement onset (Spearman's r = -0.54, p = 0.003, 95% CI [-0.77 to -0.18]). Discussion: Our results provide new insights into the precise temporal changes of ERD after hemiparetic stroke and the associations they have with motor deficits. After stroke, the average amplitude of cortical activity is reduced as compared to age-matched controls, and the extent of this decrease is correlated with the severity of motor deficits; both were true during motor programming and during motor performance. Understanding how stroke affects the temporal dynamics of cortical preparation and execution of movement paves the way for more precise restorative therapies. Studying the temporal dynamics of the EEG also strengthens the promising interest of ERD as a biomarker of post-stroke motor function.

The rhythm is going to get you.

Slow and fast movements are controlled by distinct sets of spinal V2a neurons with matching properties and connections.

Neural subspaces of imagined movements in parietal cortex remain stable over several years in humans.

Objective.A crucial goal in brain-machine interfacing is the long-term stability of neural decoding performance, ideally without regular retraining. Long-term stability has only been previously demonstrated in non-human primate experiments and only in primary sensorimotor cortices. Here we extend previous methods to determine long-term stability in humans by identifying and aligning low-dimensional structures in neural data.Approach.Over a period of 1106 and 871 d respectively, two participants completed an imagined center-out reaching task. The longitudinal accuracy between all day pairs was assessed by latent subspace alignment using principal components analysis and canonical correlations analysis of multi-unit intracortical recordings in different brain regions (Brodmann Area 5, Anterior Intraparietal Area and the junction of the postcentral and intraparietal sulcus).Main results.We show the long-term stable representation of neural activity in subspaces of intracortical recordings from higher-order association areas in humans.Significance.These results can be practically applied to significantly expand the longevity and generalizability of brain-computer interfaces.Clinical TrialsNCT01849822, NCT01958086, NCT01964261.

Context-dependence of deterministic and nondeterministic contributions to closed-loop steering control.

In natural circumstances, sensory systems operate in a closed loop with motor output, whereby actions shape subsequent sensory experiences. A prime example of this is the sensorimotor processing required to align one's direction of travel, or heading, with one's goal, a behavior we refer to as steering. In steering, motor outputs work to eliminate errors between the direction of heading and the goal, modifying subsequent errors in the process. The closed-loop nature of the behavior makes it challenging to determine how deterministic and nondeterministic processes contribute to behavior. We overcome this by applying a nonparametric, linear kernel-based analysis to behavioral data of monkeys steering through a virtual environment in two experimental contexts. In a given context, the results were consistent with previous work that described the transformation as a second-order linear system. Classically, the parameters of such second-order models are associated with physical properties of the limb such as viscosity and stiffness that are commonly assumed to be approximately constant. By contrast, we found that the fit kernels differed strongly across tasks in these and other parameters, suggesting context-dependent changes in neural and biomechanical processes. We additionally fit residuals to a simple noise model and found that the form of the noise was highly conserved across both contexts and animals. Strikingly, the fitted noise also closely matched that found previously in a human steering task. Altogether, this work presents a kernel-based analysis that characterizes the context-dependence of deterministic and non-deterministic components of a closed-loop sensorimotor task.

Precision of trunk movement in people with chronic low back pain.

BACKGROUND: Motor control exercise is commonly applied in people with chronic low back pain (CLBP), but possibly not all people with CLBP have motor control impairments. We suggest movement precision as measure to identify motor control impairments. Movement precision has been operationalized as trunk movement variability (TMV) and as trunk tracking error(s) (TTE). OBJECTIVES: To compare the known-group validity and the responsiveness of TMV and TTE. DESIGN: We used a case-control comparison (Healthy controls (n = 30) vs CLBP (n = 60)) to assess the known-group validity. A cohort study, (measurements in week 3 and week 12 of treatment), was used to assess responsiveness. METHODS: TMV (temporal (CyclSD) and spatial (MeanSD)) was analyzed during standing, repetitive flexion and rotation tasks (35x). TTE was measured during movement target tracking tasks, again in flexion and rotation. Participants with CLBP followed a multidisciplinary intervention and both measures were assessed in week 3 and week 12 of treatment. 2-way MANOVA and 2-way ANOVA were used to assess the effect of Group (CLBP vs healthy controls) and direction (flexion vs rotation) on TMV and TTE. For responsiveness, 2-way MANOVA and 2-way ANOVA were used to assess the effect of treatment and direction on both measures. FINDINGS: At baseline, TMV was not different between groups, while TTE was higher in the people with CLBP (p = 0.005, np2 = 0.09). Treatment strongly decreased temporal TMV (p = 0.025, np2 = 0.33) and TTE (p < 0.001, np2 = 0.844). CONCLUSIONS: These results demonstrate that TTE is more sensitive to CLBP and more responsive to treatment than TMV.