Time-frequency and ERP analyses of EEG to characterize anticipatory postural adjustments in a bimanual load-lifting task

Fanny Barlaam

doi:10.3389/fnhum.2011.00163

Abstract

Anticipatory postural adjustments (APAs) compensate in advance for the destabilizing effect of a movement. This study investigated the specific involvement of each primary motor cortex (M1) during a bimanual load-lifting task in which subjects were required to maintain a stable forearm position during voluntary unloading. Kinematics, electromyographic, and electroencephalographic (EEG) data were recorded in eight right-handed healthy subjects lifting a load placed on their left forearm. Two EEG analyses were performed: a time–frequency (TF) analysis and an event-related potential (ERP) analysis. The TF analysis revealed a mean power decrease in the mu rhythm over the left and right M1 concomitant with lifting onset. Each decrease showed specific features: over the right M1, contralateral to the postural forearm, there was a steeper slope and a greater amplitude than over the left M1. Although a mu rhythm desynchronization has until now been the signature of cortical activity related to a motor component, we show that it can also be related to postural stabilization. We discuss the involvement of the mu rhythm desynchronization over the postural M1 in the high temporal precision enabling efficient APAs. ERP analysis showed a negative wave over the left M1 and a concomitant positive wave over the right M1. While the negative wave classically reflects M1 recruitment related to the forthcoming lifting, the novelty here is that the positive wave reflects the transmission of inhibitory commands toward the postural forearm.

Highlights

The execution of a voluntary movement triggers postural perturbations, which can be predicted and cancelled by the central nervous system
This study investigated the specific involvement of each primary motor cortex (M1) during a bimanual load-lifting task in which subjects were required to maintain a stable forearm position during voluntary unloading
A mu rhythm desynchronization has until now been the signature of cortical activity related to a motor component, we show that it can be related to postural stabilization

Summary

Introduction

The execution of a voluntary movement triggers postural perturbations, which can be predicted and cancelled by the central nervous system. When a barman lifts up a bottle from the tray he is holding, the hand supporting the tray stays stabilized in a horizontal position, unloading the tray should provoke an upward forward movement. This is due to the use of APAs. In the experimental context, the subjects use their right (motor) hand to voluntarily lift a load placed on their left (postural) forearm (Hugon et al, 1982). APAs are characterized by a stabilization of the postural forearm due to an inhibition of the flexor muscles before the onset of unloading (Hugon et al, 1982)

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