Mirror Movements are Linked to Executive Control in Healthy and Brain-injured Adults

A neurophysiological approach to mirror movements in amyotrophic lateral sclerosis

OBJECTIVE

To investigate mirror activity in amyotrophic lateral sclerosis (ALS) patients, using a simple paradigm of signal quantification.

METHODS

Patients were asked to perform a brief isometric maximum contraction of the abductor digiti minimi (ADM) or tibialis anterior (TA) on one side, while relaxing the contralateral side of the body. Both sides were investigated. Signals were stored and analyzed offline, for quantification of electromyographic signal. Clinical signs of upper motor neuron (UMN) dysfunction, transcranial magnetic stimulation (TMS) for the upper (UL) and lower limbs (LL), the ADM ipsilateral cortical silent period (iSP) and the Edinburgh Cognitive and Behavioral ALS Screen (ECAS) cognitive scale were also investigated.

RESULTS

42 ALS patients were included. In the 4 investigated muscles the amount of mirror activity was significantly higher than in the matched healthy group. The amount of mirror activity was similar between sides, but significantly higher in UL and LL with abnormal TMS results for ADM (p = 0.005) and TA (p = 0.002), as well as in UL with abnormal iSP values (p = 0.009). No association was found between mirror activity and clinical signs of UMN involvement.

CONCLUSIONS

Mirror activity is a common phenomenon in ALS. Mirror activity intensity corresponds to the severity of UMN dysfunction, as measured by TMS, and probably derives from the abnormal transcallosal inhibition as mirrored by iSP abnormality.

SIGNIFICANCE

Mirror activity is increased in ALS and is associated with abnormal transcallosal inhibition and UMN dysfunction.

Exploring high-density corticomuscular networks after stroke to enable a hybrid Brain-Computer Interface for hand motor rehabilitation

BACKGROUND

Brain-Computer Interfaces (BCI) promote upper limb recovery in stroke patients reinforcing motor related brain activity (from electroencephalogaphy, EEG). Hybrid BCIs which include peripheral signals (electromyography, EMG) as control features could be employed to monitor post-stroke motor abnormalities. To ground the use of corticomuscular coherence (CMC) as a hybrid feature for a rehabilitative BCI, we analyzed high-density CMC networks (derived from multiple EEG and EMG channels) and their relation with upper limb motor deficit by comparing data from stroke patients with healthy participants during simple hand tasks.

METHODS

EEG (61 sensors) and EMG (8 muscles per arm) were simultaneously recorded from 12 stroke (EXP) and 12 healthy participants (CTRL) during simple hand movements performed with right/left (CTRL) and unaffected/affected hand (EXP, UH/AH). CMC networks were estimated for each movement and their properties were analyzed by means of indices derived ad-hoc from graph theory and compared among groups.

RESULTS

Between-group analysis showed that CMC weight of the whole brain network was significantly reduced in patients during AH movements. The network density was increased especially for those connections entailing bilateral non-target muscles. Such reduced muscle-specificity observed in patients was confirmed by muscle degree index (connections per muscle) which indicated a connections' distribution among non-target and contralateral muscles and revealed a higher involvement of proximal muscles in patients. CMC network properties correlated with upper-limb motor impairment as assessed by Fugl-Meyer Assessment and Manual Muscle Test in patients.

CONCLUSIONS

High-density CMC networks can capture motor abnormalities in stroke patients during simple hand movements. Correlations with upper limb motor impairment support their use in a BCI-based rehabilitative approach.

Aged Patients With Severe Small Vessel Disease Exhibit Poor Bimanual Coordination During the Anti-Phase Horizontal Line Drawing Task

The present study explores whether SVD affects bimanual coordination, which is easier to detect than by conventional, MRI-based methods. We tested nine severe SVD patients, eight non-severe (i.e., moderate or mild) SVD patients, eleven healthy age-matched controls, and eight young adults. They were grouped according to Fazekas scale and by age. Participants performed horizontal line drawings with both hands simultaneously on two pen tablets. The movements consisted of rhythmic patterns where participants used both hands to draw horizontal lines in anti-phase on two pen tablets. Each participant underwent a series of neuropsychiatric assessments. Results showed that SVD patients exhibited in each hand smaller horizontal movement amplitudes with variability larger compared to the healthy age-matched controls. Only movement amplitudes appeared to decrease significantly with severity of SVD. Interestingly, we found no relevant differences between the age-matched, elderly controls and the young controls. Therefore, this effect appeared indicative of SVD. The variability of the lines orthogonal to the horizontal lines of the left, non-dominant hand differed only between the severe SVD group and the other groups. Furthermore, partial correlations demonstrated that the mean horizontal movement amplitude of the left hand was positively associated with the clock drawing test score, and the inter-manual asynchrony of the horizontal movements was positively associated with the Trail Making Test-B time. These results indicated that SVD patients show poor bimanual coordination, as reflected by spatial features such as movement amplitudes and variabilities, and abnormal bimanual coordination was associated with executive dysfunction.

Spectral properties of physiological mirror activity: an investigation of frequency features and common input between homologous muscles

During unilateral contractions, muscular activation can be detected in both active and resting limbs. In healthy populations, the latter is referred to as physiological mirror activity (pMA). The study of pMA holds implications for clinical applications as well as the understanding of bilateral motor control. However, the underlying mechanisms of pMA remain to be fully resolved. A commonality of prevailing explanatory approaches is the concept of shared neural input. With this study, we, therefore, aimed to investigate neural input in the form of multiple analyses of surface electromyography (sEMG) recordings in the frequency domain. For this purpose, 14 healthy, right-handed males aged 18–35 years were recruited. All participants performed a pinch-force task with the dominant hand in a blockwise manner. In total, 9 blocks of 5 contractions each were completed at 80% of maximum force output. Muscle activity was recorded via sEMG of the first dorsal interosseous muscle of the active and resting hand. We analyzed (1) spectral features as well as (2) intermuscular coherence (IMC). Our results demonstrate a blockwise increase in median frequency, mean frequency, and peak frequency in both hands. Frequency ratio analyses revealed a higher low-frequency component in the resting hand. Although we were able to demonstrate IMC on an individual level, results varied greatly and grand-averaged IMC failed to reach significance. Taken together, our findings imply an overlap of spectral properties between active and passive hands during repeated unilateral contractions. Combined with evidence from previous studies, this suggests a common neural origin between active and resting hands during unilateral contractions possibly resulting from a reduction in interhemispheric inhibition due to high force demands. Nevertheless, the exploratory nature of this study necessitates the classification of our results through follow-up studies.

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.

Corticomuscular and Intermuscular Coupling in Simple Hand Movements to Enable a Hybrid Brain-Computer Interface

Hybrid Brain-Computer Interfaces (BCIs) for upper limb rehabilitation after stroke should enable the reinforcement of "more normal" brain and muscular activity. Here, we propose the combination of corticomuscular coherence (CMC) and intermuscular coherence (IMC) as control features for a novel hybrid BCI for rehabilitation purposes. Multiple electroencephalographic (EEG) signals and surface electromyography (EMG) from 5 muscles per side were collected in 20 healthy participants performing finger extension (Ext) and grasping (Grasp) with both dominant and non-dominant hand. Grand average of CMC and IMC patterns showed a bilateral sensorimotor area as well as multiple muscles involvement. CMC and IMC values were used as features to classify each task versus rest and Ext versus Grasp. We demonstrated that a combination of CMC and IMC features allows for classification of both movements versus rest with better performance (Area Under the receiver operating characteristic Curve, AUC) for the Ext movement (0.97) with respect to Grasp (0.88). Classification of Ext versus Grasp also showed high performances (0.99). All in all, these preliminary findings indicate that the combination of CMC and IMC could provide for a comprehensive framework for simple hand movements to eventually be employed in a hybrid BCI system for post-stroke rehabilitation.

Behavioural and cerebral asymmetries of mirror movements are specific to rhythmic task and related to higher attentional and executive control

Mirror movements (MM) refer to the involuntary movements or contractions occurring in homologous muscles contralateral to the unilateral voluntary movements. This behavioural manifestation increases in elderly. In right-handed adults, some studies report asymmetry in MM production, with greater MM in the right dominant hand during voluntary movements of the left non-dominant hand than the opposite. However, other studies report contradictory results, suggesting that MM asymmetry could depend on the characteristics of the task. The present study investigates the behavioural asymmetry of MM and its associated cerebral correlates during a rhythmic task and a non-rhythmic task using low-force contractions (i.e., 25 % MVC). We determined the quantity and the intensity of MM using electromyography (EMG) and cerebral correlates through electroencephalography (EEG) in right-handed healthy young and middle-aged adults during unimanual rhythmic vs. non-rhythmic tasks. Overall, results revealed (1) behavioural asymmetry of MM specific to the rhythmic task and irrespective of age, (2) cerebral asymmetry of motor activations specific to the rhythmic task and irrespective of age and (3) greater attentional and executive activations in the rhythmic task compared to the non-rhythmic task. In line with our hypotheses, behavioural and cerebral motor asymmetries of MM seem to be specific to the rhythmic task. Results are discussed in terms of cognitive-motor interactions: greater attentional and executive control required in the rhythmic tasks could contribute to the increased occurrence of involuntary movements in both young and middle-aged adults.

Task-specific and variability-driven activation of cognitive control processes during motor performance

It has long been postulated that cognitive and motor functions are functionally intertwined. While the idea received convincing support from neuroimaging studies providing evidence that motor and cognitive processes draw on common neural mechanisms and resources, findings from behavioral studies are rather inconsistent. The purpose of the present study was to identify and verify key factors that act on the link between cognitive and motor functions. Specifically we investigated whether it is possible to predict motor skills from cognitive functions. While our results support the idea that motor and cognitive functions are functionally intertwined and different motor skills entail distinct cognitive functions, our data also strongly suggest that the impact of cognitive control processes on motor skill proficiency depends on performance variability, i.e. on how challenging a motor task is. Based on these findings, we presume that motor skills activate specific cognitive control processes on two levels: basic processes that are solely related to the type of the motor task, and variability-driven processes that come into play when performance variability is high. For practitioners, these findings call for specific and challenging motor training interventions to directly tap into the to-be-improved cognitive skills and to involve a maximum of cognitive processes.