Biology subjects

Mourey, F.

Publications and source records attributed to Mourey, F..

6 recordsLinked to original sources

bioRxiv2024

Targeting a specific motor control process reveals an age-related compensation that adapts movement to gravity environment

As the global population ages, it is crucial to understand sensorimotor compensation mechanisms. These mechanisms are thought to enable older adults to remain in good physical health, but despite important research efforts, they remain essentially chimeras. A major problem with their identification is the ambiguous interpretation of age-related alterations. Whether a change reflects deterioration or compensation is difficult to determine. Here we compared the electromyographic and kinematic patterns of different motor tasks in younger (n = 20; mean age = 23.6 years) and older adults (n = 24; mean age = 72 years). Building on the knowledge that humans take advantage of gravity effects to minimize their muscle effort, we probed the ability of younger and older adults to plan energetically efficient movement during arm-only and whole-body movements. In line with previous studies and compared to younger adults, muscle activation patterns revealed that older adults used a less efficient movement strategy during whole-body movement tasks. We found that this age-related alteration was task-specific. It did not affect arm movements, thereby supporting the hypothesis that healthy older adults maintain the ability to plan energetically efficient movements. More importantly, we found that the reduced whole-body movement efficiency was correlated with kinematic measures of balance control (i.e., the center-of-mass movement amplitude and speed). The more efficient the movement strategy, the more challenging the balance. Overall, these results suggest that reduced movement efficiency in healthy older adults does not reflect a deterioration but rather a compensation process that adapts movement strategy to the task specificities. When balance is at stake, healthy older adults prefer stability to energy efficiency.

neuroscience↗

bioRxiv2023

Speed-dependent optimization of gravity effects for motor control

Several sensorimotor control studies have provided evidence supporting that the central nervous system optimizes gravitys effects to minimize muscle effort. Recently, this hypothesis has been supported by the consistent observation of direction-specific negative epochs in the phasic electromyographic signal of antigravity muscles during vertical arm movements. This suggests that gravity torque is harvested to produce some of the arms motion. However, further investigation is needed to more finely understand how the CNS integrates gravity effects into muscle commands. Here, we aimed to analyze the phasic muscular activity across varying movement speeds during horizontal and vertical arm movements. We quantified the amount of negativity during acceleration and deceleration phases for all movement directions during fast, natural, and slow movements. We found that the negativity was more important during the acceleration phase of downward movements and during the deceleration phase of upward movements, resulting in diminished phasic activity compared to horizontal movements. Concomitantly, we found direction-specific effects of movement speed on phasic EMG activity of gravity muscles. This resulted in altered EMG to kinematics relationships in vertical movements compared to horizontal ones. These results support the Effort-minimization hypothesis and confirm that the negativity of phasic EMG is an important aspect of the motor command. Furthermore, the present results reveal that the CNS finely tunes this feature across a range of movement speeds and directions.

neuroscience↗

bioRxiv2022

Motor imagery training is beneficial for motor memory of upper and lower limb tasks in very old adults

Human aging is associated with a decline in the capacity to memorize recently acquired motor skills. Motor imagery training is a beneficial method to compensate for this deterioration in old adults. It is not yet known whether these beneficial effects are maintained in very old adults (>80 years), more affected by the degeneration processes. The aim of this study was to evaluate the effectiveness of a mental training session of motor imagery on the memorization of new motor skills acquired through physical practice in very old adults. Thirty very old adults performed 3 actual trials of a manual dexterity task (session 1) or a sequential footstep task (session 2) as fast as they could before and after a 20-min motor imagery training (mental-training group) or watching a documentary for 20 min (control group). Performance was improved after 3 actual trials for both tasks and both groups. For the control group, performance decreased in the manual dexterity task after the 20-min break and remained stable in the sequential stepping task. For the mental-training group, performance was maintained in the manual dexterity task after the 20-min motor imagery training and increased in the sequential stepping task. These results extended the benefits of motor imagery training to the very old population, showing that even a short motor imagery training improved their performance and favor the motor memory process. These results confirmed that motor imagery training is an effective method to complement traditional rehabilitation protocols.

neuroscience↗

bioRxiv2021

Gravity effects are better optimized by older than young adults when reaching with the non-dominant arm

Motor lateralization refers to differences in the neural organization of cerebral hemispheres, resulting in different control specializations between the dominant and the non-dominant motor systems. Multiple studies proposed that the dominant hemisphere is specialized for open-loop optimization-like processes. Recently, comparing arm kinematics between upward and downward movements, we found that the dominant arm outperformed the non-dominant one regarding gravity-related motor optimization in healthy young participants. The literature about aging effects on motor control presents several neurophysiological and behavioral evidences for an age-related reduction of motor lateralization. Here, we compare the lateralization of a well-known gravity-related optimal motor control process between young and older adults. Forty-one healthy young (mean age = 24.3 {+/-} 3 years) and forty-two healthy older adults (mean age = 72.0 {+/-} 6 years) performed single degree-of-freedom vertical arm movements between two targets (upward and downward). Participants alternatively reached with their dominant and non-dominant arms. We recorded arm kinematics and electromyographic activities of the prime movers (Anterior and Posterior Deltoids) and we analyzed parameters thought to represent the hallmark of the gravity-related optimization process (i.e directional asymmetries and negative epochs on the phasic EMG activity). We found strong age x arm interaction effects on all parameters; i.e., relative durations to peak acceleration and peak velocity and the negativity of antigravity muscles phasic signals. Although all three parameters showed a lateralization effect where the dominant arm was superior to the non-dominant arm in young adults (as in Poirier et al. 2022), we found no such effect in older adults. With both arms, the results of older adults lied between those of the dominant and non-dominant arm of young adults. These results add to those of recent literature showing that feedforward motor control remains functional in older adults. More, the results obtained with the non-dominant arm may support a previously hypothesized increased reliance on predictive mechanisms in older adults.

neuroscience↗

bioRxiv2021

Muscle effort is best minimized by the right-dominant arm in the gravity field

The central nervous system (CNS) is thought to develop motor strategies that minimize various hidden criteria, such as end-point variance or effort. A large body of literature suggests that the dominant arm is specialized for such open-loop optimization-like processes whilst the non-dominant arm is specialized for closed-loop control. Building on recent results suggesting that the brain plans arm movements that takes advantage of gravity effects to minimize muscle effort, the present study tests the hypothesized superiority of the dominant arm motor system for effort minimization. Thirty participants (22.5 {+/-} 2.1 years old; all right-handed) performed vertical arm movements between two targets (40{degrees} amplitude), in two directions (upwards and downwards) with their two arms (dominant and non-dominant). We recorded the arm kinematics and the electromyographic activity of the anterior and posterior deltoid to compare two motor signatures of the gravity-related optimization process; i.e., directional asymmetries and negative epochs on phasic muscular activity. We found that these motor signatures were still present during movements performed with the non-dominant arm, indicating that the effort-minimization process also occurs for the non-dominant motor system. However, these markers were reduced compared with movements performed with the dominant arm. This difference was especially prominent during downward movements, where the optimization of gravity effects occurs early in the movement. Assuming that the dominant arm is optimal to minimize muscle effort, as suggested by previous studies, the present results support the hypothesized superiority of the dominant arm motor system for effort-minimization.

neuroscience↗

bioRxiv2019

Motor planning of vertical arm movements in healthy older adults: does effort optimization persist with aging?

Several sensorimotor modifications are known to occur with aging, possibly leading to adverse outcomes such as falls. Recently, some of those modifications have been proposed to emerge from motor planning deteriorations. Motor planning of vertical movements is thought to engage an internal model of gravity to anticipate its mechanical effects on the body-limbs and thus to genuinely produce movements that minimize muscle effort. This is supported, amongst other results, by direction-dependent kinematics where relative durations to peak accelerations and peak velocity are shorter for upward than for downward movements. The present study compares motor planning of fast and slow vertical arm reaching movements between eighteen young (24 {+/-} 3 years old) and seventeen older adults (70 {+/-} 5 years old). We found that older participants still exhibit directional asymmetries (i.e., differences between upward and downward movements), indicating that optimization processes during motor planning persist with healthy aging. However, the size of these differences was increased in older participants, indicating that gravity-related motor planning changes with age. We discuss this increase as the possible result of an overestimation of gravity torque or increased weight of the effort cost in the optimization process. Overall, these results support the hypothesis that feedforward processes and, more precisely, optimal motor planning, remain active with healthy aging.

neuroscience↗