Intracortical Inhibition Within the Primary Motor Cortex Can Be Modulated by Changing the Focus of Attention

Summary

Using two different transcranial magnetic stimulation (TMS) protocols, this manuscript describes how to measure and compare cortical inhibition within the primary motor cortex when adopting different attentional foci.

Abstract

It is well recognized that an external focus (EF) compared with an internal focus (IF) of attention improves motor learning and performance. Studies have indicated benefits in accuracy, balance, force production, jumping performance, movement speed, oxygen consumption, and fatiguing task. Although behavioral outcomes of using an EF strategy are well explored, the underlying neural mechanisms remain unknown. A recent TMS study compared the activity of the primary motor cortex (M1) between an EF and an IF. More precisely, this study showed that, when adopting an EF, the activity of intracortical inhibitory circuits is enhanced.

On the behavioral level, the present protocol tests the influence of attentional foci on the time to task failure (TTF) when performing submaximal contractions of the first dorsal interosseous (FDI). Additionally, the current paper describes two TMS protocols to assess the influence of attentional conditions on the activity of cortical inhibitory circuits within the M1. Thus, the present article describes how to use single-pulse TMS at intensities below the motor threshold (subTMS) and paired-pulse TMS, inducing short-interval intracortical inhibition (SICI) when applied to the M1. As these methods are assumed to reflect the responsiveness of GABAergic inhibitory neurons, without being affected by spinal reflex circuitries, they are well suited to measuring the activity of intracortical inhibitory circuits within the M1.

The results show that directing attention externally improves motor performance, as participants were able to prolong the time to task failure. Moreover, the results were accompanied by a larger subTMS-induced electromyography suppression and SICI when adopting an EF compared to an IF. As the level of cortical inhibition within the M1 was previously demonstrated to influence motor performance, the enhanced inhibition with an EF might contribute to the better movement efficiency observed in the behavioral task, indicated by a prolonged TTF with an EF.

Introduction

It is now generally accepted that adopting an EF compared to an IF or neutral focus of attention promotes motor performance and learning in numerous settings¹. It has been shown, for example, that adopting an EF leads to benefits in accuracy^2,3, balance^4,5,6, force production^7,8, jumping performance^7,9,10,11, ....

Protocol

This protocol was approved by the local ethics committee, and the experiments are in accordance with the Declaration of Helsinki (1964).

1. Ethical Approval and Subject Instruction

1. Before starting the measurement, instruct all participants about the potential risk factors and the purpose of the study. Do not give information about the attentional foci, as this might affect the results. Ensure that the safety guidelines for the application of TMS in research settings ³⁰ are followed.
   NOTE: When applying TMS, there are some medical risk factors, including implanted cranial electrodes and cochlear imp....

Results

The Influence of Attentional Foci on Motor Performance:

The behavioral tests in the current study were used to prove the feasibility of the motor task and to identify the subjects who reacted positively when applying an EF. In line with previous studies (see¹ for a review), our results show a prolonged TTF when the participants adopted an EF compared to an IF (see Figure 3). Thu.......

Discussion

This protocol shows two possible methods to investigate the activity of inhibitory circuits within the M1 using TMS. More precisely, these two protocols have been used in this study to investigate the impact of attentional foci on the activity of inhibitory circuits within the M1.

One limitation of the presented method is that it is not always possible to cause a subTMS-induced EMG suppression without a facilitation preceding it. In this study, for example, four subjects had to be removed from.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
MC3A-100	Advanced Mechanical Technologies Inc., Watertown, MA, USA	-	Force transducer
BlueSensor P	Ambu A/S, Bellerup, Denmark	-	Ag/AgCl surface electrodes for EMG
Polaris Spectra	Northern Digital, Waterloo, ON, Canada	-	neuronavigation system, active or passive markers tracker
Localite TMS Navigator Version 2.0.5	LOCALITE GmbH, Sankt Augustin, Germany	-	navigation system for transcranial magnetic stimulation (TMS)
MagVenture MagPro X100	MagVenture A/S, Farum, Denmark	9016E0711	Transcranial magnetic stimulator
MagVenture D-B80	MagVenture A/S, Farum, Denmark	9016E0431	TMS coil (figure of eight)
Goniometer	N/A	-	Custom-made goniometer
Othopedic splint	N/A	-	Custom-made splint
Recording software	LabView based	-	Custom-made script