Name: intracortical inhibition within the primary motor cortex can be modulated by changing the focus of attention
Uploaded: 2017-09-11T12:30:00
Description: Watch this Scientific Journal Video about Intracortical Inhibition Within the Primary Motor Cortex Can Be Modulated by Changing the Focus of Attention at JoVE.com

The authors have no acknowledgements.

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
<ol>
	<li>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 <sup class="xre...

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...

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 accuracy2,3, balance4,5,6, force production7,8, jumping performance7,9,10,11, movement speed12, oxygen consumption13,14, and fatiguing tasks15,16.
On the other side, since brain activation is the basis of all movements, several aspects of the neural control of movement have been investigated. For example, the level and the ability to modulate intracortical inhibition within the M1 has been shown to have a strong influence on motor function, such as interlimb coordination17, postural control18, and dexterity19. Furthermore, populations with poorer motor control abilities than young adults, such as elderly subjects or children (born preterm20), usually show less pronounced inhibitory control. Thus, although the role of inhibitory processes is not yet well understood, inhibitory processes nevertheless seem to be important to the quality of motor execution in general.
A possibility to investigate intracortical inhibitory circuitries is to use non-invasive transcranial magnetic stimulation (TMS). The most commonly used stimulation protocol applies paired-pulse TMS (ppTMS) to induce SICI. This protocol uses a conditioning stimulus below the motor threshold to reduce the amplitude of the suprathreshold control stimulus response elicited at an interstimulus interval of 1-5 ms21,22,23,24. Then, reported as the percentage of the control stimulus, the amplitudes of the motor-evoked potentials (MEPs) can be compared across conditions, giving information about cortical inhibitory activity and modulation within the M1.
Another stimulation protocol to assess the activity of intractortical inhibitory circuits applies single pulses, where all stimuli are delivered at intensities below the motor threshold (i.e., subTMS). This protocol induces suppression in the ongoing EMG activity18,25,26. This so-called subTMS-induced EMG suppression can be compared in terms of amount and duration. Although this protocol is not so commonly used, it has certain advantages compared to the standard SICI protocol. This protocol does not disturb motor execution, as it does not induce suprathreshold stimuli. Both methods test the responsiveness of intracortical gamma-aminobutyric acid (GABA) inhibitory interneurons23,27.
Despite the well-known benefits of using an EF compared to an IF on motor performance1, the underlying neural processes remain largely unknown. In a former fMRI study28, it was shown that blood-oxygen level-dependent (BOLD) activation was enhanced in the M1, primary somatosensory, and insular cortices when subjects executed a finger sequence and adopted an EF compared to an IF. As excitatory and inhibitory activity cannot be differentiated by fMRI29, another recent study16 stipulated that the enhanced activity in the M1 associated with an EF could, in fact, be due to the enhanced activity of intracortical inhibitory circuits. More precisely, this study showed that the excitability of inhibitory GABAergic neurons can be modulated instantly by the type of attentional focus adopted in one and the same person.
The main aim of the present protocol is to show two possible ways to compare the immediate effects of cognitive manipulation (i.e., focus of attention instructions) on the activity of intracortical inhibitory circuits within the M1. SubTMS and ppTMS are both used. In addition, this protocol shows one possible way to explore the influence of attentional foci on motor behavior in a very controlled way by investigating the TTF of submaximal isometric sustained contraction of the FDI.

<table width="1053">
	<tbody>
		<tr height="42">
			<td height="42" style="width:268px;height:42px;">MC3A-100</td>
			<td style="width:255px;">Advanced Mechanical Technologies Inc., Watertown, MA, USA</td>
			<td style="width:112px;">-</td>
			<td style="width:419px;">Force transducer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">BlueSensor P</td>
			<td style="width:255px;">Ambu A/S, Bellerup, Denmark</td>
			<td>-</td>
			<td>Ag/AgCl surface electrodes for EMG</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Polaris Spectra</td>
			<td style="width:255px;">Northern Digital, Waterloo, ON, Canada</td>
			<td>-</td>
			<td>neuronavigation system, active or passive markers tracker</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Localite TMS Navigator Version 2.0.5</td>
			<td style="width:255px;">LOCALITE GmbH, Sankt Augustin, Germany</td>
			<td>-</td>
			<td>navigation system for transcranial magnetic stimulation (TMS)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MagVenture MagPro X100</td>
			<td style="width:255px;">MagVenture A/S, Farum, Denmark</td>
			<td>9016E0711</td>
			<td>Transcranial magnetic stimulator</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MagVenture D-B80</td>
			<td style="width:255px;">MagVenture A/S, Farum, Denmark</td>
			<td style="width:112px;">9016E0431</td>
			<td>TMS coil (figure of eight)</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:268px;height:21px;">Goniometer</td>
			<td style="width:255px;">N/A</td>
			<td style="width:112px;">-</td>
			<td>Custom-made goniometer</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:268px;height:21px;">Othopedic splint</td>
			<td style="width:255px;">N/A</td>
			<td style="width:112px;">-</td>
			<td>Custom-made splint</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:268px;height:21px;">Recording software</td>
			<td>LabView based</td>
			<td style="width:112px;">-</td>
			<td>Custom-made script</td>
		</tr>
	</tbody>
</table>

intracortical inhibition within the primary motor cortex can be modulated by changing the focus of attention

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.

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...

Watch this Scientific Journal Video about Intracortical Inhibition Within the Primary Motor Cortex Can Be Modulated by Changing the Focus of Attention at JoVE.com

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

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.

It is well recognized that an external focus (EF) compared with an internal focus (IF) of attention improves motor learning and performance. Studies have ...

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