In-phase Movements Research Articles

Increasing thigh extension with haptic feedback affects leg coordination in young and older adult walkers.

Interlimb coordination can be used as a metric to study the response of the neuromuscular system to mechanical perturbations and behavioral information. Behavioral information providing haptic feedback on thigh angle has been shown to increase stride length and consequently walking speed, but the effect of such feedback on limb coordination has not been determined. The current work investigates the effects of this feedback on lower-limb coordination and examines if such effects are dependent on the age of the walker. Existing kinematic data were examined from 10 young and 10 older adults during overground walking at self-selected normal and fast speeds and with thigh extension haptic feedback. Using sagittal angles of the lower-limb segments, we quantified changes in the mean of continuous relative phase (ACRP) and its standard deviation (VCRP) for thigh-shank and shank-foot segment pairs, over windows of 10% of gait cycle around peak thigh extension, toe-off, and heel strike. We found that the haptic feedback resulted in more in-phase movement (i.e., decreased ACRP, Cohen's d: 0.56-1.46), and larger coordination variability (i.e., increased VCRP, Cohen's d: 0.60-1.50) of the segment pairs across the three windows. Additionally, the young adults exhibited lower ACRP than older adults (Cohen's d=1.02) and higher VCRP (Cohen's d=1.02) when the feedback was provided. The results suggest that the haptic feedback elicited distinct adaptations in the neuromuscular system and that this response differed between young and older adults.

The impact of lesion side on bilateral upper limb coordination after stroke

BackgroundA stroke frequently results in impaired performance of activities of daily life. Many of these are highly dependent on effective coordination between the two arms. In the context of bimanual movements, cyclic rhythmical bilateral arm coordination patterns can be classified into two fundamental modes: in-phase (bilateral homologous muscles contract simultaneously) and anti-phase (bilateral muscles contract alternately) movements. We aimed to investigate how patients with left (LHS) and right (RHS) hemispheric stroke are differentially affected in both individual-limb control and inter-limb coordination during bilateral movements.MethodsWe used kinematic measurements to assess bilateral coordination abilities of 18 chronic hemiparetic stroke patients (9 LHS; 9 RHS) and 18 age- and sex-matched controls. Using KINARM upper-limb exoskeleton system, we examined individual-limb control by quantifying trajectory variability in each hand and inter-limb coordination by computing the phase synchronization between hands during anti- and in-phase movements.ResultsRHS patients exhibited greater impairment in individual- and inter-limb control during anti-phase movements, whilst LHS patients showed greater impairment in individual-limb control during in-phase movements alone. However, LHS patients further showed a swap in hand dominance during in-phase movements.ConclusionsThe current study used individual-limb and inter-limb kinematic profiles and showed that bilateral movements are differently impaired in patients with left vs. right hemispheric strokes. Our results demonstrate that both fundamental bilateral coordination modes are differently controlled in both hemispheres using a lesion model approach. From a clinical perspective, we suggest that lesion side should be taken into account for more individually targeted bilateral coordination training strategies.Trial registration: the current experiment is not a health care intervention study.

Intentional maintenance of antiphase bimanual pattern at transition frequency: Is it associated with inhibition processes?

This study aimed at demonstrating the intentional modulation of bimanual coordination dynamics at transition frequency and determining whether it is associated with perceptual and/or motor inhibition capacities. Healthy adults (N = 29) performed in a random order: i) bimanual anti-phase (AP) movements at the maximal individual transition frequency, with the instruction to either let go, or intentionally maintain the initial movement pattern and oppose to the spontaneous transition to in-phase (IP) movements, and ii) The Motor and Perceptual Inhibition Test, giving separate scores for perceptual and motor inhibition. Results showed that in the intentional condition participants were able to delay (more movement cycles before the transition) and suppress (more trials without transition) the spontaneous transition from AP to IP. A statistically significant, though weak, correlation was found between motor performance and perceptual inhibition scores. We interpreted our findings as an indicator of the presence of an inhibitory mechanism underlying intentional dynamics that is partially associated to perceptual inhibition in healthy adults. This could have implications in populations with compromised inhibitory capacities, which might entail motor repercussions, and suggests the possibility of using bimanual coordination as means to stimulate both cognitive and motor capacities.

Motor Control Studies on Bimanual Coordination - Does the Left Hand not Know What the Right Hand is Doing? -

운동조절학적 관점에서 양손은 협응을 통해 조화롭게 움직이므로 오른손이 하는 일을 왼손이 모르게 하는 것은 불가능하다. 양손 움직임의 리듬, 진폭(길이), 방향이 대칭이거나 동위상으로 움직일 때 안정적인 협응 패턴이 관찰되고, 한손의 움직임이 다른 손의 움직임에 영향을 미친다는 사실을 보여준다. 뇌량은 대뇌 좌우 반구의 정보를 교환하는 역할로 양손 협응에 기여한다. 하지만, 협응 능력은 특정 부위의 기능에 의존적이지 않고, 상황에 따라 다양한 신경 조합들의 상호작용으로 유도된다. 인간의 협응 능력을 고려할 때, “오른손이 하는 일을 왼손이 모르게 하라”는 예수의 말씀은 ‘자신도 모르게 하라’는 새롭게 해석된다.It is impossible to keep the left hand from knowing what the right hand is doing in a motor control perspective. Bimanual movements are closely linked through coordination to perform harmonious movements. The optimal coordination pattern can be observed when the rhythm, amplitude (length), direction are constrained in the bimanual movements. Symmetrical or in-phase movements between the limbs demonstrate the basic human coordination pattern, which is characterized by stable movements. When performing a bimanual task, the movement of one hand affects the movement of the other hand because information about left and right movement is exchanged via the corpus callosum. Given the functions and roles of the brain, it appears that coordination is not dependent on a single locus of the brain, but rather appears as a result of the interaction of different neural combinations depending on the situation. Although the mechanism underlying bimanual coordination has yet to be fully understood, it is clear that the left and right hands are inextricably linked and influence each other's movements. Thus, ‘don't let the left hand know what the right hand is doing’ means a lack of self-consciousness of one’s deeds.

Temporal synchronization for in-phase and antiphase movements during bilateral finger- and foot-tapping tasks.

Appropriate motor performance, which must be precisely processed and timed to temporal and spatial requirements, can be studied using a synchronized tapping task. For gait rehabilitation, estimation of bilateral foot-tapping accuracy is important, as walking involves bilateral movements, usually antiphase, of the lower extremities. Rhythmic control of lower limb movements, such as gait, involves voluntary control and may also be automatically regulated by the central pattern generator. This study investigated the temporal synchronization of in-phase and antiphase movements using synchronized bilateral finger and foot-tapping tasks. Thirty healthy young adult volunteers were enrolled and instructed to tap the finger or foot button synchronously with the tones presented at fixed inter-stimulus intervals (ISIs). One of 10 different ISIs (250-4800ms) was selected for each block, in which 110 tones were presented. Taps were performed by either unilateral or bilateral fingers or feet, either in-phase (to move bilateral fingers or ankles simultaneously) or antiphase (to move bilateral fingers or ankles alternately). The synchronization error (SE) and coefficient of variation (CV) of the inter-tap interval (ITI) were evaluated. In all trials with short ISIs, SEs were narrowly distributed, either clustered around 0ms or with a slightly negative value. Although SE variability gradually increased with increasing ISI, the CV of ITI was significantly lower for antiphase movement than for unilateral or in-phase movement in the foot-tapping task, but not in the finger-tapping task. The preserved temporal synchronization for antiphase movement of the foot, but not finger tapping, may be due to the neural mechanisms underlying locomotion.

Relação entre a coordenação motora e a função executiva em adultos e idosos

ABSTRACT Brazilian older adults present a relatively low schooling level when compared with other populations. In clinical practice, defining if more subtle alterations observed in executive function (EF) and motor coordination tests in older adults are due to an initial neurological condition or low schooling level is difficult. This study aimed to evaluate the possible differences in motor coordination and EF between adults and older adults with high and low schooling level as well as the possible correlations between motor coordination and EF in this sample. A total of 75 healthy individuals (aged from 30 to 89 years) were evaluated. EF was assessed by the trail making test (TMT) whereas motor coordination was assessed by the upper limb diadochokinetic test, which is the rapid alternation between supination and pronation of the forearms (right, left, both performing in-phase movements, and both performing anti-phase movements). Analysis of variance showed that age and schooling level possibly influenced EF and motor coordination. Possible relationships between EF and diadochokinesis were calculated by Pearson’s correlation. Older adults with low schooling level were significantly slower on the TMT part B (cognitive and motor) and delta TMT (cognitive). All groups were slower performing the anti-phase movement, especially those with low schooling level. Results showed only weak correlations between EF and motor coordination. Age and schooling level influenced executive function and motor coordination. However, the EF and motor coordination tests presented no correlation when these two factors were statistically corrected.

Task-specific fear influences abnormal trunk motor coordination in workers with chronic low back pain: a relative phase angle analysis of object-lifting

BackgroundPain-related fear influences impaired trunk movement (e.g., limited movement of range and velocity), but it is unclear how fear relates to trunk motor coordination (e.g., a more “in-phase” upper-lower trunk motion pattern). We conducted the present study to: (1) identify the motor coordination pattern of the in-phase upper-lower lumbar movements during the lifting, and (2) determine how pain-related fear is related to the trunk coordination pattern in workers with chronic low back pain (CLBP).MethodsWe examined 31 male workers with CLBP (CLBP group) and 20 healthy controls with no history of CLBP (HC group). The movement task was lifting a box, the weight of which was 10, 30%, or 50% of the subject’s body weight. We used a 3D motion capture system to calculate the mean absolute relative phase angle (MARP) angle as an index of coordination and the mean deviation phase (DP) as an index of variability. We used a numerical rating scale to assess the subjects’ task-specific fear.ResultsThe MARP angle during trunk extension movement in the 50% condition was significantly decreased in the CLBP group compared to the HCs; i.e., the upper lumbar movement was more in-phase with the lower lumbar movement. The hierarchical multiple regression analysis results demonstrated that a decreased MARP angle was associated with high task-specific fear.ConclusionsA more ‘in-phase’ upper-lower lumbar movement pattern was predicted by task-specific fear evoked when performing a work-related activity. Our findings suggest that an intervention for task-specific fear may be necessary to improve an individual’s impaired trunk motor coordination.

Effect of External Feedback on Bimanual Coordination Control in Patients with Parkinson's Disease.

Bimanual coordination control requires task-specific control of the spatial and temporal characteristics of the coupling of both upper limbs. The present study examined the effects of external feedback (i.e., auditory signal) on bimanual coordination movement during patients with Parkinson’s disease (PD). Twelve PD patients in advanced stages and 12 early stages of untreated PD patients, and 12 age-matched normal adults were instructed to perform bimanual coordination control using preference (1 Hz) and fast (1.75 Hz) speeds with metronome auditory cue. The results demonstrated that the advanced PD patients showed reduced synchronized bimanual coordination control during the anti-phase movement compared with other two groups. Moreover, the decreased movement accuracy was exhibited not only at the preference speed, but also more particularly at the fast speed with anti-phase rather than in-phase movement. This suggests that PD results in impairments in scaling the bimanual movement speed and amplitude of limb, and these deficits were more pronounced as a function of movement control speed. Overall, the current data provide evidence of the pathophysiology of the basal ganglia on the bimanual coordination movement.

Trunk-pelvic coordination during unstable sitting with varying task demand: A methodological study

Unstable sitting is used commonly to evaluate trunk postural control (TPC), typically via measures based on center-of-pressure (CoP) time series. However, these measures do not directly reflect underlying control/movement strategies. We quantified trunk-pelvis coordination during unstable sitting using vector coding (VC) and correlated such coordination with CoP-based outcomes across varying task demands. Thirteen uninjured individuals (11 male/2 female) sat on an unstable chair at four instability levels, in a random order, defined relative to the individual gravitational gradient (∇G): 100, 75, 60, and 45%∇G. VC assessed trunk-pelvic coordination, and coupling angles classified movements as: 1) anti-phase, 2) in-phase, 3) trunk-phase, or 4) pelvic-phase. With decreasing %∇G (i.e., increasing instability), we found: increased anti-phase movement in the sagittal and frontal planes; decreased in-phase movement in the sagittal and frontal planes; and increased in-phase and pelvic-phase movement in the transverse plane. In the sagittal and frontal planes, we observed significant weak-to-moderate correlations between anti-phase and in-phase movements (0.288 < |ρ| < 0.549). Correlations between CoP-based measures and pelvic-phase and trunk-phase movements were typically weak and/or non-significant (|ρ| < 0.318). VC techniques discriminated between levels of instability during unstable sitting, identifying in-phase coordination (stiffening strategy) at lower instability levels and anti-phase coordination at higher instability levels. Compared to CoP-based measures, trunk coordination outcomes during unstable sitting provide measures of TPC that more directly quantify underlying movement strategies. These results can also serve as a baseline for future work investigating populations with impaired TPC (e.g., individuals with low back pain or limb loss).

Analysis of connections and restrictions occurring due to the oscillations of vibrating screen working member and cantilevered screen deck

Research relevance is due to the need of mining companies in a more complete extraction of mineral resources, reduction of crude minerals losses, and extension of deposits’ life. Some enterprises face the problem of complicated high-quality separation of hard-to-screen rock mass. Screen which are common in the industry often become clogged causing decline in the effectiveness of screening. Research aim is to determine the links, build resonant curves and analyze the amplitude oscillations of the working member and cantilevered bars of the screen deck using numerical simulation. Methodology includes the theoretical study of the dual mass oscillatory system with the use of numerical simulation. Results. The motion of the vibrating screen with circular oscillations of the working member, which includes the screen deck of a cascade type with cantilevered bars, is regarded as oscillation of a dual mass system. The amplitudes of oscillations of both masses make in-phase and anti-phase movements relative to the driving force of the drive. The analysis showed that the amplitudes of the working member are practically independent of the screen deck parameters, and bars oscillation amplitudes vary over a wide range. The expressions are given calculating the parameters of cantilevered bars and the values of the initial data of the GIT-51 screen. Resonance curves of amplitude and frequency relations are constructed. The conditions are established under which the oscillation amplitudes of the cantilevered bars take on hyperadmissible values; it is shown that for a particular oscillating system there is a transitional resonance value. Summary. The natural oscillation frequency ratio ranges are established of the entire system with the frequency of forced oscillations in which the oscillation amplitudes of cantilevered bars reach the specified parameters. It is shown that by changing the screen deck parameters at the design stage, it is possible to adjust the inter-frequency range and establish the operating mode of the screen.

Using visual and/or kinesthetic information to stabilize intrinsic bimanual coordination patterns is a function of movement frequency.

Coordination dynamics suggest that both in-phase and anti-phase movements are intrinsic and can be readily performed without practice. As movement frequency increases, individuals performing anti-phase movement inevitably switch to perform in-phase movement. However, due to different frames of reference used to define intrinsic coordination patterns in visual and kinesthetic domains, the perception of intrinsic coordination patterns could be ambiguous, which leads to the question whether the visually or kinesthetically perceived information is used to maintain the intrinsic coordination patterns. The current study explored how the consistency between visual and kinesthetic information would impact the performance and the associated metabolic energy consumption of intrinsic bimanual coordination patterns as movement frequency increased. Thirty participants were recruited and randomly assigned to one of three groups ("Info + Spatial +", "Info + Spatial -", and "Info-Spatial +") to perform intrinsic bimanual coordination tasks using a computer-joystick system at low, high, and self-selected frequencies. The visual and kinesthetic information were manipulated to be either consistent or inconsistent by changing the spatial mapping between the motion of display and motion of joysticks. The results showed that the kinesthetic information was largely used to maintain the stability of intrinsic coordination patterns at high frequency, which could be an energy-conserving solution. However, spatial mapping alone seemed to be beneficial for keeping the visually perceived in-phase and anti-phase coordination patterns equally stable at low movement frequency, and spatially mapping the visual information to be consistent with kinesthetic information greatly enhanced the stability of anti-phase coordination. The dynamical use of visual and kinesthetic information for control of bimanual coordination is discussed.

P2-13-07. Temporal processing between in-phase and antiphase movements during bilateral finger and foot tapping tasks

P2-13-07. Temporal processing between in-phase and antiphase movements during bilateral finger and foot tapping tasks

Kinematic profiles suggest differential control processes involved in bilateral in-phase and anti-phase movements

In-phase and anti-phase movements represent two basic coordination modes with different characteristics: during in-phase movements, bilateral homologous muscle groups contract synchronously, whereas during anti-phase movements, they contract in an alternating fashion. Previous studies suggested that in-phase movements represent a more stable and preferential bilateral movement template in humans. The current experiment aims at confirming and extending this notion by introducing new empirical measures of spatiotemporal dynamics during performance of a bilateral circle drawing task in an augmented-reality environment. First, we found that anti-phase compared to in-phase movements were performed with higher radial variability, a result that was mainly driven by the non-dominant hand. Second, the coupling of both limbs was higher during in-phase movements, corroborated by a lower inter-limb phase difference and higher inter-limb synchronization. Importantly, the movement acceleration profile between bilateral hands followed an in-phase relationship during in-phase movements, while no specific relationship was found in anti-phase condition. These spatiotemporal relationships between hands support the hypothesis that differential neural processes govern both bilateral coordination modes and suggest that both limbs are controlled more independently during anti-phase movements, while bilateral in-phase movements are elicited by a common neural generator.

Multiscale movement coordination dynamics in collaborative team problem solving

During collaborative problem solving (CPS), coordination occurs at different spatial and temporal scales. This multiscale coordination should play a functional role in facilitating effective collaboration. To evaluate this, we conducted a study of computer-based CPS with 42 dyadic teams. We used cross-wavelet coherence to examine movement coordination, extracted from videos, at several scales, and tested whether the observed coordination was greater than expected due to chance and due to task demands. We found that coordination at scales less than 2s was greater than chance and at most scales (except 16s, 1m, and 2m), was greater than expected due to task demands. Lastly, we observed that coherence at .25s and 1s scales was predictive of performance. However, when including relative phase, our results suggest that higher in-phase movement coordination at the 1s scale was the strongest predictor of CPS performance. Further, we used growth curve modeling to examine how movement coordination changes across the duration of the task and whether this is moderated by CPS performance. We found that coordination over the duration of the CPS task is quadratic (a U shape) and that better performing teams have higher coordination with a shallower curve. We discuss these findings and their relevance to understanding how low-level movement coordination facilitates CPS.

Functional connectivity during monitoring for visuomotor incongruence.

Previous human studies on monitoring for visuomotor incongruence emphasized the contribution of the fronto-parietal network and revealed significant activation of the right dorsolateral prefrontal cortex (DLPFC) and the right rostral inferior parietal lobule. Using functional MRI, this study investigated the brain regions involved in explicit monitoring for incongruence between motor intention and visual and/or proprioceptive information, particularly focusing on the fronto-parietal network. During in-phase bimanual movements, a static image of the participant's own hands was randomly inserted within real-time visual feedback of the movements to produce a mismatch between the actual performance and the visual input. The results of our task were similar to those of previous studies, in that greater activity was observed in the right DLPFC during incongruence conditions than during congruence conditions. However, the anatomical location of the DLPFC cluster was found in a more ventral region, compared with previous studies. Psychophysiological interaction analysis for the entire brain, using the right DLPFC as a seed region, indicated significantly greater functional connectivity with the bilateral dorsal premotor cortex, middle temporal gyri (area V5), and right rostral inferior parietal lobule (area PFt).

Learning to balance on a slackline: Development of coordinated multi-joint synergies.

Previous research has investigated synergies involved in locomotion and balance reactions; however, there is limited insight into the emergence of skilled balance control with practice of challenging tasks. We explored motor learning of tandem and single leg stance on an unstable surface-a slackline. Balance was tested in 10 naïve healthy adults at four time points: baseline, after one slackline practice session, after 1week of practice, and 1week following the final practice session. We recorded kinematics of the upper and lower arms bilaterally, trunk, and thigh and foot unilaterally while participants balanced in tandem and single leg stance on a slackline and narrow rigid beam (transfer task). When participants first attempted to stand on the slackline, they exhibited fast and frequent movements across all joints with actions along the frontal plane (particularly the hip) and fell after a short period (~3seconds). Performance improved rapidly (fewer falls), and this was accompanied by dampened trunk and foot oscillations and the development of coordinated movement patterns with a progressive emphasis on more distal upper body segments. Continuous relative phase angles between joint pairs began to cluster around either 0° (indicating in-phase movement) or 180° (indicating anti-phase movement). Participants also began to demonstrate coordinated upper body synergies and performance improvements (fewer falls) on the transfer task, while a control group (n=10) did not exhibit similar synergies or performance improvements. Our findings describe the emergence of coordinated movement synergies involving the upper body as healthy adults learn a challenging balance task.

S149. Improved bimanual control in elderly after motor cortex stimulation

Introduction Accompanying the natural advancing of age is a decline in cognitive and motor functions, which may be the result of altered neuroplasticity, due to changes in synaptic function and neurotransmission. Successful performance of routine, but complex motor tasks such as bimanual movements may require optimal synchronization of motor cortical areas, which decline with ageing. On the other hand, recent work has shown that transcranial direct current stimulation (tDCS) may be a useful tool to restitute these altered mechanisms, and improve performance of motor skills. Presently, we address the question of identifying physiological markers of age-related differences during acquisition of new bimanual motor control tasks, based on induced oscillatory changes, using EEG. Second, we assess whether performance of complex bimanual skills can be improved in the elderly using tDCS. Methods Experiment 1 : 43 healthy subjects (21 elderly) performed the bimanual tracking task (BTT), which is a complex task requiring multiple cognitive domains, as well as the skilled use of in-phase and anti-phase movements, at various frequencies. Three blocks of the task were performed (180 total trials) while EEG was recorded to measure task-induced power changes. Experiment 2 : An additional 40 subjects (20 elderly) were recruited for evaluating whether right M1 anodal tDCS (1.0 mA, 20 min) may improve performance in the task, particularly in the non-dominant left hand. The study was double-blinded, sham-controlled, and employed a randomized crossover design in order to assess tDCS-induced performance and task-induced synchronization differences between young and elderly groups. Results Experiment 1: Overall task performance in younger subjects was more accurate than in elderly. Younger subjects showed significantly stronger desynchronization in the mu and beta band, whereas older subjects showed greater gamma band activity in motor cortical areas. In addition, these patterns were also found to correlate inter-individually with accurate performance in the task. Experiment 2: ANOVA revealed a main effect of stimulation, which was significant between active and sham tDCS conditions in the elderly but not in young. Further exploratory analyses revealed significant improvements in both left and right hand coordination in active stimulation conditions for both groups of subjects, with the greatest improvement found in left-hand dominant motor movements in the elderly group. Conclusion We show that both task-induced oscillatory synchronization and inter-limb kinematics underlying bimanual motor coordination are different between the young and elderly. Further, a single session of tDCS applied to the motor cortex could significantly improve bimanual performance in the elderly. Although further studies are needed to optimize tDCS parameters for enhanced and prolonged effects, tDCS may be a viable tool in restituting the learning of complex motor functions in the aging or other vulnerable populations.

O-2-40. Comparisons of functional EEG network during performing different bimanual motor tasks using graph theoretical analysis

Graph theoretical approach is emerging as a powerful tool for analyzing brain functional network. To compare functional electroencephalography (EEG) network between inphase and anti-phase of bimanual hand movement, 10 healthy subjects were carried out experiments. In the clustering coefficient (CC), the alpha band of dominant motor area (C3) and the beta band of non-dominant motor area (C4) during anti-phase movement were higher than those of in-phase movement. In the betweenness centrality (BC), the alpha band of C3 during anti-phase movement was lower than those of in-phase movement. On the other hand, the gamma band of C4 during anti-phase movement was higher than those of in-phase movement. Additional analysis revealed that patient with stroke in the left middle cerebral artery infraction tended to low CC both movement and low BC during anti-phase movement. Our findings suggest that task-specific functional network alterations reflect on these graph theoretical parameters. In conclusion, the graph theoretical analysis applied to EEG network during bimanual hand movement has a potential to evaluate the brain network function.

Double negative acoustic metastructure for attenuation of acoustic emissions

Acoustic metamaterials hold great potential for attenuation of low frequency acoustic emissions. However, a fundamental challenge is achieving high transmission loss over a broad frequency range. In this work, we report a double negative acoustic metastructure for absorption of low frequency acoustic emissions in an aircraft. This is achieved by utilizing a periodic array of hexagonal cells interconnected with a neck and mounted with an elastic membrane on both ends. An average transmission loss of 56 dB under 500 Hz and an overall absorption of over 48% have been realized experimentally. The negative mass density is derived from the dipolar resonances created as a result of the in-phase movement of the membranes. Further, the negative bulk modulus is ascribed to the combined effect of out-of-phase acceleration of the membranes and the Helmholtz resonator. The proposed metastructure enables absorption of low frequency acoustic emissions with improved functionality that is highly desirable for varied applications.

P315 Investigating bimanual motor coordination in healthy young and older adults using EEG and transcranial direct current stimulation (tDCS)

Introduction Accompanying the natural advancing of age is a decline in cognitive and motor functions, which can significantly impact the daily life activities in the elder demographic (>65 y). Such declines may involve altered neuroplasticity, due to changes in synaptic function and neurotransmission. Successful performance of complex motor tasks may also entail distinct patterns in motor cortical functional connectivity, which may also be subject to age related changes. On the other hand, recent work has shown that transcranial direct current stimulation (tDCS) may be a useful tool to restitute these altered mechanisms, and improve performance of motor skills. Objectives The present study first addresses the question of identifying physiological markers of age-related differences during acquisition and performance of bimanual motor movements, based on motor cortical functional connectivity using EEG. Second, the study assesses whether performance of complex bimanual motor skills can be improved in the elderly using tDCS. Methods Experiment 1 : 42 healthy, non-smoking subjects (20 young/22 elderly) were recruited. Subjects performed a bimanual tracking task similar to the classic “Etch-a-Sketch” game, which requires in-phase and anti-phase movements, and at various frequencies. Three blocks of the task were performed (180 total trials) in the single-session design to evaluate both kinematic and EEG metrics (phase lag functional connectivity) between the young and elderly. Experiment 2 : An additional 40 subjects (20 young/20 elderly) were recruited for evaluating whether right M1 anodal tDCS (1.0 mA, 20 min) may improve performance in the task. A double-blinded, sham-controlled, randomized crossover design was implemented to assess kinematic and functional connectivity differences between young and elderly. Data was statistically analyzed within the framework of mixed-design ANOVAs, in order to assess overall group differences in performance, as well as main effects of stimulation, across three incrementing levels of task difficulty. Results Experiment 1 : Task performance in younger subjects was more accurate than elderly. Elderly showed higher beta power during planning and performance periods. Lateralized motor cortical functional connectivity to prefrontal cortical areas was also greater in younger subjects, whereas elderly subjects showed no discrimination in activation during tasks that relied more on one hand. Experiment 2 : ANOVA revealed a main effect of stimulation in elderly but not in young. Post hoc analyses revealed significant improvements in both left and right hand coordination in real stimulation conditions. Younger subjects tended to improve performance as well, although ceilings effects may have been a constraint. In further post hoc analyses, we observed that older subjects favored slower, but accurate movement coordination whereas younger participants divided evenly in the speed vs. accuracy dichotomy. Conclusion We show that both functional connectivity and inter-limb kinematics underlying bimanual motor coordination are different between the young and elderly. Such differences may be due to constraints in muscular strength, degeneration of the gray matter, and/or differences in cortical connectivity as a result of the aging process. We further show that a single session of tDCS applied to the motor cortex was able to significantly improve the bimanual performance in both young and elderly. Although further studies are needed to optimize tDCS parameters for enhanced and prolonged effects, this non-invasive stimulation technique may be a viable tool in restituting and even further optimizing motor functioning. Download high-res image (183KB) Download full-size image