Online proprioception feeds plasticity of arm representation following tool-use in healthy aging

Salam Bahmad,Richard Moreau,Alessandro Farnè,Luke E Miller,Romeo Salemme,Minh Tu Pham,Eric Koun,Alice C Roy

doi:10.1038/s41598-020-74455-5

Abstract

Following tool-use, the kinematics of free-hand movements are altered. This modified kinematic pattern has been taken as a behavioral hallmark of the modification induced by tool-use on the effector representation. Proprioceptive inputs appear central in updating the estimated effector state. Here we questioned whether online proprioceptive modality that is accessed in real time, or offline, memory-based, proprioception is responsible for this update. Since normal aging affects offline proprioception only, we examined a group of 60 year-old adults for proprioceptive acuity and movement’s kinematics when grasping an object before and after tool-use. As a control, participants performed the same movements with a weight—equivalent to the tool—weight-attached to their wrist. Despite hampered offline proprioceptive acuity, 60 year-old participants exhibited the typical kinematic signature of tool incorporation: Namely, the latency of transport components peaks was longer and their amplitude reduced after tool-use. Instead, we observed no kinematic modifications in the control condition. In addition, online proprioception acuity correlated with tool incorporation, as indexed by the amount of kinematics changes observed after tool-use. Altogether, these findings point to the prominent role played by online proprioception in updating the body estimate for the motor control of tools.

Highlights

Following tool-use, the kinematics of free-hand movements are altered
We compared the proprioceptive acuity between young and old adults to ascertain whether our sample of old adults displayed the expected decline in the offline (IRR/Ipsilateral Remembered Left (IRL)) as compared to online proprioception (CCM)
We assessed them for the emergence of the pattern of kinematic changes that has been previously reported following tool-use in young adults

Summary

Introduction

Following tool-use, the kinematics of free-hand movements are altered. This modified kinematic pattern has been taken as a behavioral hallmark of the modification induced by tool-use on the effector representation. Online proprioception acuity correlated with tool incorporation, as indexed by the amount of kinematics changes observed after tool-use These findings point to the prominent role played by online proprioception in updating the body estimate for the motor control of tools. These findings point toward a critical role played by proprioception in lengthening the estimated metrics of the arm, which would influence subsequent movements execution, when the tool is no longer h eld[11] This raises the question of whether online, or memory-based proprioception is responsible for the changes in free hand kinematics following tool-use. Old adults are reported with a deficit regarding mostly the offline, as compared to the online access to proprioceptive inputs[17,18]

Methods

Results

Conclusion