Name: force and position control in humans - the role of augmented feedback
Uploaded: 2016-06-19T13:00:00
Description: Watch this Scientific Journal Video about Force and Position Control in Humans - The Role of Augmented Feedback at JoVE.com

The authors have no acknowledgements.

The protocol described here followed the guidelines of the ethics committee of the University of Freiburg and was in accordance with the declaration of Helsinki (1964).
1. Ethical Approval - Subject Instruction
<ol>
	<li>Before the actual experiment, instruct all subjects about the purpose of the study and potential risk factors. When applying transcranial magnetic stimulation (TMS), there are some medical risks including any history of epileptic seizures, metal implants in eyes and/or head,...

The present study investigated if the interpretation of augmented feedback influences the time to fatigue of a sustained submaximal contraction and the neural processing of the primary motor cortex. The results show that as soon as the participants interpreted the feedback as position feedback (compared to force feedback), the time to fatigue was significantly shorter and the inhibitory activity of the motor cortex (measured as the amount of EMG suppression caused by subTMS) is greater. As the task did not change between...

Sensory feedback is crucial to perform movements. Daily activities are hardly possible in the absence of proprioception 1. Furthermore, motor learning is influenced by proprioceptive integration 2 or cutaneous perception 3. Healthy humans with intact sensation are able to weight the sensory inputs arising from various sensory sources in order to meet situation-specific needs 4. This sensory weighing enables humans to perform difficult tasks with high precision even when some aspects of the sensory information are unreliable or even absent (e.g., walking in the dark or with eyes closed).
Additionally, various evidence suggests that providing augmented (or additional) feedback further improves motor control and/or motor learning. Augmented feedback provides additional information by an external source which can be added to the task intrinsic (sensory) feedback arising from the sensory system 5,6. Especially the effect of the content of augmented feedback on motor control and learning has been of great interest in recent years. One of the questions addressed was how humans control force and position 7,8. Initial investigations identified differences in time to fatigue of a sustained submaximal contraction using either position or force feedback and differences in load compliance (e.g., 9-12). When subjects were provided with force feedback, the time to fatigue of the sustained contraction was significantly longer compared to when position feedback was provided. The same phenomenon was observed for a variety of different muscles and limb positions and a number of neuromuscular mechanisms, including a greater rate of motor unit recruitment and a greater decrease in H-reflex area during the position controlled contraction (for review 13). However, in these studies, not only the visual feedback but also the physical characteristics of the muscular contraction (i.e., the compliance of the measurement device) was altered. Therefore, we recently conducted a study not altering compliance but only augmented feedback and provided evidence that provision of force and position feedback alone during a sustained submaximal contraction can cause differences in inhibitory activity within the primary motor cortex (M1). This was shown using a stimulation technique that is known to act solely at the cortical level 14, namely subthreshold transcranial magnetic stimulation (subTMS). Unlike suprathreshold TMS, the response evoked by subTMS, is not modulated by the excitability of spinal &#945;-motoneurons and the excitability excitatory neurons and/or cortical cells 15-17 but solely by the excitability of inhibitory intracortical neurons. The postulated mechanism behind this stimulation technique is that it is applied at intensities below the threshold to evoke a motor evoked potential (MEP). It was shown in patients having electrodes implanted at the cervical level that this type of stimulation does not produce any descending activity but that it primarily activates inhibitory interneurons within the primary motor cortex 14,18,19. This activation of inhibitory interneurons causes a decrease in the ongoing EMG activity and can be quantified by the amount of EMG suppression compared to the EMG activity obtained in trials without stimulation. In this respect, we showed that subjects displayed a significantly greater inhibitory activity in trials in which they received position feedback compared with trials in which force feedback was provided 20. Furthermore, we also showed that not only the presentation of different feedback modalities (force vs. position control) but also the interpretation of feedback can have very similar effects on behavioural and neurophysiological data. More specifically, when we told the participants to receive position feedback (even though it was force feedback) they also not only displayed a shorter time to fatigue but also an increased level of inhibitory M1 activity 21. Using an approach where the same feedback but with different information about its content is always provided has the advantage that the task constraints, i.e., the presentation of the feedback, the gain of the feedback, or the compliance of the load are identical between conditions so that differences in performance and neural activity are clearly related to differences in the interpretation of the feedback and are not biased by different testing conditions. Thus, the current study investigated whether a different interpretation of one and the same feedback influences the duration of a sustained submaximal contraction and furthermore has an impact on the activation of inhibitory activity of the primary motor cortex.

<table border="0" cellpadding="0" cellspacing="0" width="796">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">torquemeter</td>
			<td>LCB 130, ME-Mebsysteme, Neuendorf, Germany</td>
			<td></td>
			<td style="width:167px;">Part of robotic device built for force and position recordings</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">potentiometer</td>
			<td>type 120574, Megatron, Putzbrunn, Germany</td>
			<td style="width:119px;"></td>
			<td>Part of robotic device built for force and position recordings</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EMG electrodes</td>
			<td>Blue sensor P, Ambu, Bad Nauheim, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">TMS coil</td>
			<td>Magstim</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">TMS machine</td>
			<td>Magstim Company Ltd., Whitland, UK</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Recording software</td>
			<td style="width:295px;">Labview-Based</td>
			<td style="width:119px;"></td>
			<td>custom written software</td>
		</tr>
	</tbody>
</table>

force and position control in humans - the role of augmented feedback

During motor behaviour, humans interact with the environment by for example manipulating objects and this is only possible because sensory feedback is constantly integrated into the central nervous system and these sensory inputs need to be weighted in order meet the task specific goals. Additional feedback presented as augmented feedback was shown to have an impact on motor control and motor learning. A number of studies investigated whether force or position feedback has an influence on motor control and neural activation. However, as in the previous studies the presentation of the force and position feedback was always identical, a recent study assessed whether not only the content but also the interpretation of the feedback has an influence on the time to fatigue of a sustained submaximal contraction and the (inhibitory) activity of the primary motor cortex using subthreshold transcranial magnetic stimulation. This paper describes one possible way to investigate the influence of the interpretation of feedback on motor behaviour by investigating the time to fatigue of submaximal sustained contractions together with the neuromuscular adaptations that can be investigated using surface EMG. Furthermore, the current protocol also describes how motor cortical (inhibitory) activity can be investigated using subthreshold TMS, a method known to act solely on the cortical level. The results show that when participants interpret the feedback as position feedback, they display a significantly shorter time to fatigue of a submaximal sustained contraction. Furthermore, subjects also displayed an increased inhibitory activity of the primary cortex when they believed to receive position feedback compared when they believed to receive force feedback. Accordingly, the results show that interpretation of feedback results in differences on a behavioural level (time to fatigue) that is also reflected in interpretation-specific differences in the amount of inhibitory M1 activity.

Interpretation of feedback
In procedure described here, subjects were instructed in a way that they believed in half of their trials to have received position feedback and in the other half of the trials to have received force feedback. In fact, they were tricked in half of their trials as they the pF-group always received position feedback and the fF-group always received force feedback.
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Watch this Scientific Journal Video about Force and Position Control in Humans - The Role of Augmented Feedback at JoVE.com

Force and Position Control in Humans - The Role of Augmented Feedback

Controlling an identical movement with position or force feedback results in different neural activation and motor behavior. This protocol describes how to investigate behavioral changes by looking at neuromuscular fatigue and how to evaluate motor cortical (inhibitory) activity using subthreshold TMS with respect to the interpretation of augmented feedback.

During motor behaviour, humans interact with the environment by for example manipulating objects and this is only possible because sensory feedback is ...

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