Biology subjects

Poirier, G.

Publications and source records attributed to Poirier, G..

7 recordsLinked to original sources

bioRxiv2024

Evidence for flexible motor costs in vertical arm movements: reduced gravity-related effort minimization under high accuracy constraints

The central nervous system (CNS) is thought to use motor strategies that minimize several criteria, such as end-point variability or effort, to plan optimal motor patterns. In the case of vertical arm movements, a large body of literature demonstrated that the brain uses a motor strategy that takes advantage of the mechanical effects of gravity to minimize muscle effort. Results from other studies suggested that the relative importance of each criterion may vary according to the tasks constraints. For example, it could be hypothesized that reduced end-point variability driven by high accuracy demands is detrimental to effort minimization. The present study probes this specific hypothesis using the framework of gravity-related effort minimization. We asked twenty young healthy participants to perform vertical arm reaching movements towards targets whose size varied across conditions. We recorded the arm kinematics and electromyographic activities of the anterior deltoid to study two well-known motor signatures of the gravity-related optimization process; i.e., directional asymmetries on velocity profiles and negative epochs on phasic muscular activities. The results showed that both indices were reduced as target size decreased, demonstrating that the gravity-related optimization process was reduced under high accuracy constraints. This phenomenon is consistent with the use of a trade-off strategy between effort and end-point variability. More generally, it suggests that the CNS is able to appropriately modulate the relative importance of varied motor costs when facing varying task demands.

neuroscience↗

bioRxiv2023

pADP-ribosylation Regulates the Cytoplasmic Localization, Cleavage and Pro-apoptotic Function of HuR

HuR (ElavL1) is one of the main posttranscriptional regulators that determines cell fate. While the role of HuR in apoptosis is well-established, the posttranslational modifications that governs this function remain elusive. In this study we show that PARP1/2-mediated poly(ADP)-ribosylation (PARylation) is instrumental in the pro-apoptotic function of HuR. During apoptosis or in cells depleted of PARP1/2 enzymes, a substantial reduction in HuR PARylation is observed. This results in the cytoplasmic accumulation and the cleavage of HuR, both of which are essential events for apoptosis. These effects are mediated by a pADP-ribose (PAR) binding motif within the HuR-HNS region (HuR PAR Binding Site (HuR-PBS)). Under normal conditions, the association of HuR-PBS with PAR is responsible for the nuclear retention of HuR. Mutations within this motif prevents the binding of HuR to its import factor TRN2, leading to its cytoplasmic accumulation and cleavage. Collectively, our findings underscore the role of PARylation in controlling the proapoptotic function of HuR, offering insight into the mechanism by which PARP1/2 enzymes regulate cell fate and adaptation to various assaults.

cell biology↗

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↗

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↗

bioRxiv2020

Drosophila dTBCE recruits tubulin around chromatin to promote mitotic spindle assembly

Proper assembly of mitotic spindles requires microtubule nucleation at centrosomes but also around chromatin. In this study, we reveal a novel mechanism by which an enrichment of tubulin in the nuclear space following nuclear envelope breakdown promotes nucleation of spindle microtubules. This event mediated by the tubulin-specific chaperone dTBCE, depends on its tubulin binding CAP-Gly motif and is regulated by Ran. Live imaging, proteomic and biochemical analyses suggest that dTBCE is enriched in the nucleus at nuclear envelope breakdown and interacts with nuclear pore proteins and the Ran machinery to create an environment that facilitates subsequent tubulin enrichment. We propose that dTBCE-dependent increase in tubulin concentration in the nuclear space is an important mechanism for microtubule nucleation in organisms where compartmentalization prevents free diffusion of tubulin.

cell biology↗

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↗