A cross-species neural integration of gravity for motor optimisation

Abstract

15Recent kinematic results, combined with model simulations, have provided support for the 16 hypothesis that the human brain uses an internal model of gravity to shape motor patterns that 17 minimise muscle effort. Because many different muscular activation patterns can give rise to 18 the same trajectory, here we analyse muscular activation patterns during single-degree-of-19 freedom arm movements in various directions, which allow to specifically investigating 20 gravity-related movement properties. Using a well-known decomposition method of tonic and 21 phasic electromyographic activities, we demonstrate that phasic EMGs present systematic 22 negative phases. This negativity demonstrates that gravity effects are harvested to save 23 muscle effort and reveals that the brain implements an optimal motor plan using gravity to 24 accelerate downward and decelerate upward movements. Furthermore, for the first time, we 25 compare experimental findings in humans to monkeys, thereby generalising the Effort-26 optimization strategy across species. 27 the velocity and acceleration of the limb -and the gravity forces -related to the position of 51

Motor Planning of Vertical Arm Movements in Healthy Older Adults: Does Effort Minimization Persist With Aging?

“…In young adults, several studies have shown that singledegree-of-freedom arm movements exhibit directional asymmetries in the vertical plane. These asymmetries: (i) were consistently reported as a more abrupt acceleration phase for upward than for downward movements; (ii) do not exist in the horizontal plane (Gentili et al, 2007;Le Seac'h and McIntyre, 2007); (iii) progressively disappear in the vertical plane when participants are exposed to microgravity (Papaxanthis et al, 2005;Gaveau et al, 2016); (iv) were observed very early in the movements [before 70 ms after movement start Gaveau et al, 2014)]; and (v) were explained by optimal control model simulations and EMG analyses as a motor strategy that minimizes muscle effort (Berret et al, 2008;Crevecoeur et al, 2009;Gaveau et al, 2014Gaveau et al, , 2016Gaveau et al, , 2019. Altogether, in young adults, previous results strongly suggest that direction-dependent kinematics represent the signature of a motor planning strategy that optimally integrates gravity torque to save muscle effort.…”

“…Consequently, directiondependent kinematics has been proposed to represent the signature of a motor planning strategy that optimally integrates gravity torque to save muscle effort. Recent electromyographic (EMG) analyses further support this concept (Gaveau et al, 2019).…”

“…Using arm reaching tasks, several studies have investigated gravity-related motor planning in young adults (Gentili et al, 2007;Le Seac'h and McIntyre, 2007;Crevecoeur et al, 2009;Gaveau et al, , 2014Gaveau et al, , 2016Bringoux et al, 2012;Sciutti et al, 2012;Yamamoto and Kushiro, 2014;Hondzinski et al, 2016;Yamamoto et al, 2016;Olesh et al, 2017;Gaveau et al, 2019;Yamamoto et al, 2019). A consistent outcome is the existence of direction-dependent arm kinematics in normal gravity, which progressively disappears in microgravity (Papaxanthis et al, 2005;Gaveau et al, 2016).…”

Deterioration, Compensation and Motor Control Processes in Healthy Aging, Mild Cognitive Impairment and Alzheimer’s Disease

“…Young adults are known to use an optimal strategy that minimizes muscle effort. Directional asymmetries can quantify this strategy, i.e., differences between upward and downward movements [ 60 , 61 , 62 , 63 ]. Poirier et al (2020) observed that young and older participants exhibited qualitatively similar directional asymmetries, thereby indicating that older adults can unfold the same effort-related optimization strategy as young adults.…”

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

“…McIntyre 2007); iii) progressively disappear in the vertical plane when participants are exposed to microgravity (Papaxanthis et al 2005;Gaveau et al 2016); iv) were observed very early in the movements (before 70ms after movement start (Gaveau and Papaxanthis 2011;Gaveau et al 2014); v) were explained by optimal control model simulations and EMG analyses as a motor strategy that minimizes muscle effort (Berret et al 2008;Crevecoeur et al 2009;Gaveau et al 2014Gaveau et al , 2016Gaveau et al , 2019. Altogether, in young adults, previous results strongly suggest that direction-dependent kinematics represent the signature of a motor planning strategy that optimally integrates gravity torque to save muscle effort.…”