How Thoughts Give Rise to Action - Conscious Motor Intention Increases the Excitability of Target-Specific Motor Circuits

Volker R Zschorlich,Rüdiger Köhling,Alessandro D′Ausilio

doi:10.1371/journal.pone.0083845

Abstract

The present study shows evidence for conscious motor intention in motor preparation prior to movement execution. We demonstrate that conscious motor intention of directed movement, combined with minimally supra-threshold transcranial magnetic stimulation (TMS) of the motor cortex, determines the direction and the force of resulting movements, whilst a lack of intention results in weak and omni-directed muscle activation. We investigated changes of consciously intended goal directed movements by analyzing amplitudes of motor-evoked potentials of the forearm muscle, flexor carpi radialis (FCR), and extensor carpi radialis (ECR), induced by transcranial magnetic stimulation over the right motor cortex and their motor outcome. Right-handed subjects were asked to develop a strong intention to move their left wrist (flexion or extension), without any overt motor output at the wrist, prior to brain stimulation. Our analyses of hand acceleration and electromyography showed that during the strong motor intention of wrist flexion movement, it evoked motor potential responses that were significantly larger in the FCR muscle than in the ECR, whilst the opposite was true for an extension movement. The acceleration data on flexion/extension corresponded to this finding. Under no-intention conditions again, which served as a reference for motor evoked potentials, brain stimulation resulted in undirected and minimally simultaneous extension/flexion innervation and virtually no movement. These results indicate that conscious intentions govern motor function, which in turn shows that a neuronal activation representing an “intention network” in the human brain pre-exists, and that it functionally represents target specific motor circuits. Until today, it was unclear whether conscious motor intention exists prior to movement, or whether the brain constructs such an intention after movement initiation. Our study gives evidence that motor intentions become aware before any motor execution.

Highlights

Movement preparation in voluntary movement is a complex process of different cooperating brain areas
We investigated the changes of consciously intended movement aims in the motor preparation phase and their motor outcome using kinetic data and motorevoked potentials (MEP) induced by transcranial magnetic stimulation (TMS)
EMG raw signals from the extensor carpi radialis muscle (ECR), and the flexor carpi radialis muscle (FCR) were high-pass filtered with a digital 2nd order Butterworth filter [27] with a cut-off frequency of 5 Hz

Summary

Introduction

Movement preparation in voluntary movement is a complex process of different cooperating brain areas. One part of this process is a goal-directed movement intention Both in the fields of psychology [1,2,3], and basic neurosciences [4,5,6,7], the processes of goal-directed voluntary movement were studied intensely. In this context, closely related brain functions, such as attention and intention, were locally distinguishable from each other by functional brain imaging [4,8]. This modulation relates, i.e. to mental imagery [10,11], to external stimuli [11,12], and even to crossmodal phenomena [14,15]

Methods

Results

Conclusion