Yamaguchi A1, Sasaki A1, Milosevic M1, Nakazawa K1
1University of Tokyo, Tokyo, Japan
Background: It has previously been demonstrated that unilateral force control results in significantly less error, more force steadiness, and shorter reaction times compared to bilateral force control. It was observed only during tonic (5sec long) contraction, while during ballistic (less than 1sec long) contraction no such superior performance in unilateral control was found. However, the neural mechanisms underlying the different performances between unilateral and bilateral force control is still unkown.
Purpose: The objectives of our study were to examine corticospinal excitability evoked using transcranial magnetic stimulation (TMS) to; 1) assess the neural activation during unilateral and bilateral force control; and 2) investigate task specific neural activations during tonic and ballistic contraction of ankle dorsi-flexors.
Methods: Seven healthy young adults (male, 23.9±1.9 years) participated in this study. Participants performed isometric ankle dorsi-flexion force control tasks. The task required matching a visual target (10% of maximal effort) which appeared randomly, as quickly and precisely as possible during tonic task for 5 sec and ballistic task for less than 1 sec with unilateral and bilateral conditions. During each task, TMS was delivered in four different phases:
i) pre-contraction phase (200msec after target appearance);
ii) ascending contraction phase (50msec after electromyography on set of tibialis anterior (TA));
iii) plateau phase (4000msec after target appearance); and
iv) at rest (after the experiment).
TMS at plateau phase was only delivered during tonic task. Motor evoked potentials (MEPs) were recorded from right TA muscle using TMS on the 'hot spot' of the TA at 120% motor threshold. Peak-to-peak amplitude of MEPs were used to compare the corticospinal excitability during each experimental condition.
Results: MEP amplitude was significantly increased not only during the contraction phases but also pre-contraction phase compared to the rest state. There were no significant differences of corticospinal excitability between tonic task and ballistic task during all contraction phases. Although there was no statistically significant difference, the results showed larger facilitation of MEPs during unilateral force control compared to bilateral control during the pre-contraction phase.
Conclusion(s): Although different strategy is required during tonic and ballistic tasks (i.e., feedback control and feedforward control, respectively), it seems that corticospinal involvement during tonic contraction resembles that during ballistic contraction. This could be because voluntary engagement during both tasks facilitate neural activity in a similar way. Furthermore, our results suggested that prior to the contraction (i.e., pre-contraction phase), corticospinal excitability is facilitated in order to initiate more precise and quick force execution, especially during unilateral motor control tasks. Therefore, it seems that the greater corticospinal excitability at preparation phase is relevant to the better performance in the unilateral task.
Implications: It has been widely accepted that the neural activity enhances motor learning after stroke. With respect to the rehabilitation paradigm, taking into account the corticospinal excitability is essential for functional improvement. Our further research of fundamental mechanism of motor control will contribute to develop rehabilitation after stroke.
Keywords: Corticospinal excitability, transcranial magnetic stimulation (TMS), force control
Funding acknowledgements: The Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) [17F17733 and 26242056].
Purpose: The objectives of our study were to examine corticospinal excitability evoked using transcranial magnetic stimulation (TMS) to; 1) assess the neural activation during unilateral and bilateral force control; and 2) investigate task specific neural activations during tonic and ballistic contraction of ankle dorsi-flexors.
Methods: Seven healthy young adults (male, 23.9±1.9 years) participated in this study. Participants performed isometric ankle dorsi-flexion force control tasks. The task required matching a visual target (10% of maximal effort) which appeared randomly, as quickly and precisely as possible during tonic task for 5 sec and ballistic task for less than 1 sec with unilateral and bilateral conditions. During each task, TMS was delivered in four different phases:
i) pre-contraction phase (200msec after target appearance);
ii) ascending contraction phase (50msec after electromyography on set of tibialis anterior (TA));
iii) plateau phase (4000msec after target appearance); and
iv) at rest (after the experiment).
TMS at plateau phase was only delivered during tonic task. Motor evoked potentials (MEPs) were recorded from right TA muscle using TMS on the 'hot spot' of the TA at 120% motor threshold. Peak-to-peak amplitude of MEPs were used to compare the corticospinal excitability during each experimental condition.
Results: MEP amplitude was significantly increased not only during the contraction phases but also pre-contraction phase compared to the rest state. There were no significant differences of corticospinal excitability between tonic task and ballistic task during all contraction phases. Although there was no statistically significant difference, the results showed larger facilitation of MEPs during unilateral force control compared to bilateral control during the pre-contraction phase.
Conclusion(s): Although different strategy is required during tonic and ballistic tasks (i.e., feedback control and feedforward control, respectively), it seems that corticospinal involvement during tonic contraction resembles that during ballistic contraction. This could be because voluntary engagement during both tasks facilitate neural activity in a similar way. Furthermore, our results suggested that prior to the contraction (i.e., pre-contraction phase), corticospinal excitability is facilitated in order to initiate more precise and quick force execution, especially during unilateral motor control tasks. Therefore, it seems that the greater corticospinal excitability at preparation phase is relevant to the better performance in the unilateral task.
Implications: It has been widely accepted that the neural activity enhances motor learning after stroke. With respect to the rehabilitation paradigm, taking into account the corticospinal excitability is essential for functional improvement. Our further research of fundamental mechanism of motor control will contribute to develop rehabilitation after stroke.
Keywords: Corticospinal excitability, transcranial magnetic stimulation (TMS), force control
Funding acknowledgements: The Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) [17F17733 and 26242056].
Topic: Neurology; Human movement analysis
Ethics approval required: Yes
Institution: University of Tokyo
Ethics committee: Ethics Review Committee for Experimental Research with Human Subjects
Ethics number: 475
All authors, affiliations and abstracts have been published as submitted.
