Influence of emotion on precision grip force control: A comparison of pleasant and neutral emotion

Objective

The present study aimed to investigate the impact of emotion on force steadiness of isometric precision pinch grip that is not direction-specific.

Methods

Thirty-two healthy volunteer subjects participated in the present study. Subjects were divided into two experimental groups: pleasant image group and neutral image group. The isometric precision pinch grip task was performed for three times. Specifically, the first task was performed before pleasant or neutral picture viewing, the second task was performed immediately after picture viewing, further the third task was performed 30 seconds after the second task. During the isometric precision pinch grip task, participants were asked to exert pinch grip force at 10% of maximal voluntary contraction with visual feedback. The coefficient of variation of force production and normalized root mean square value of electromyography activity were calculated.

Results

After pleasant picture viewing, coefficient of variation of pinch force production and normalized root mean square value of electromyography was decreased. While, in the neutral image condition, theses variables were not altered. More important, compared to the neutral image condition, pleasant emotion led to lower coefficient of variation of pinch grip force production.

Conclusion

These findings indicate that pleasant emotion improves force control of isometric precision pinch grip. Therefore, in clinical settings, the emotional state of patients may affect the effectiveness of rehabilitation and should be taken into consideration.

Unpleasant visual stimuli increase the excitability of spinal motor neurons

Purpose: In physical therapy for post-stroke patients, we often experience cases in which unpleasant emotions cause abnormal muscle tonus. Previously, we suggested that the magnitude of spinal motor neuron excitability was correlated with the grade of muscle tonus. Therefore, spinal motor neuron excitability was considered to be a useful index to evaluate the influence of unpleasant emotions on muscle tonus. In this study, we investigated whether unpleasant emotions evoked by visual stimuli affected the excitability of spinal motor neurons.Materials and Methods: The F-waves, an indicator of spinal motor neuron excitability, were measured in 19 healthy adult volunteers. Firstly, for the rest trial, F-waves were measured during relaxation to determine the baseline of spinal motor neuron excitability. Following the rest trial, the unpleasant trial was conducted in which F-waves were measured while the subjects viewed an unpleasant picture for 1 min. After the unpleasant trial, F-waves were measured during relaxation. For the control condition, F-waves were measured while the subjects viewed a neutral picture instead of the unpleasant picture. The recorded F-wave data were analysed for persistence and the F/M amplitude ratio.Results: Persistence and the F/M amplitude ratio were significantly greater during the unpleasant trial than during the rest trial. In the control condition, there was no significant difference in persistence and the F/M amplitude ratio compared with the three trials.Conclusions: Our findings indicate that unpleasant emotions may affect spinal motor neuron excitability. Therefore, learning how to control emotions should be important aspect of physical therapy.

Excitability of spinal motor neurons during motor imagery of thenar muscle activity under maximal voluntary contractions of 50% and 100

[Purpose] We often perform physical therapy using motor imagery of muscle contraction to improve motor function for healthy subjects and central nerve disorders. This study aimed to determine the differences in the excitability of spinal motor neurons during motor imagery of a muscle contraction at different contraction strengths. [Subjects] We recorded the F-wave in 15 healthy subjects. [Methods] In resting trial, the muscle was relaxed during F-wave recording. For motor imagery trial, subjects were instructed to imagine maximal voluntary contractions of 50% and 100% while holding the sensor of a pinch meter, and F-waves were recorded for each contraction. The F-wave was recorded immediately after motor imagery. [Results] Persistence and F/M amplitude ratio during motor imagery under maximal voluntary contractions of 50% and 100% were significantly higher than that at rest. In addition, the relative values of persistence, F/M amplitude ratio, and latency were similar during motor imagery under the two muscle contraction strengths. [Conclusion] Motor imagery under maximal voluntary contractions of 50% and 100% can increase the excitability of spinal motor neurons. Differences in the imagined muscle contraction strengths are not involved in changes in the excitability of spinal motor neurons.

Excitability of spinal neural function during motor imagery in Parkinson's disease

the median nerve at the wrist in subjects during two motor imagery conditions: holding and not holding the sensor of a pinch meter between the thumb and index finger. Our aim was to determine whether mental simulation without the muscle contraction associated with motion can increase the excitability of spinal neural function in patients with Parkinson's disease (PD). F-waves of the left thenar muscles were examined in 10 patients with PD under resting, holding and motor imagery conditions. For the holding condition, the subjects held the sensor of the pinch meter between their thumb and index finger. For the motor imagery conditions, the subjects were asked to imagine a 50% maximal voluntary isometric contraction holding and not holding the sensor of the pinch meter between their thumb and index finger (motor imagery "with"/"without sensor"). Persistence during motor imagery under the "with sensor" condition increased significantly compared with persistence during resting (n=10, z=2.2509, p=0.0244, Wilcoxon test). The F/M amplitude ratio during motor imagery under the "with sensor" condition increased significantly compared with that during resting (n=10, z=2.1915, p=0.0284, Wilcoxon test). Excitability of spinal neural function during motor imagery in Parkinson's disease Motor imagery under the "with the sensor" condition increased excitability of the spinal neural output to the thenar muscles. Because excitability of the spinal neural output to the thenar muscles during motor imagery "with the sensor" was significantly higher than that during resting, we suggest that movement preparation for a motor imagery task is important in patients with PD.

Influence of motor imagery of isometric opponens pollicis activity on the excitability of spinal motor neurons: a comparison using different muscle contraction strengths

[Purpose] This study aimed to determine the differences in the excitability of spinal motor neurons during motor imagery of a muscle contraction at different contraction strengths. [Methods] We recorded the F-wave in 15 healthy subjects. First, in a trial at rest, the muscle was relaxed during F-wave recording. Next, during motor imagery, subjects were instructed to imagine maximum voluntary contractions of 10%, 30%, and 50% while holding the sensor of a pinch meter, and F-waves were recorded for each contraction. F-waves were recorded immediately and at 5, 10, and 15 min after motor imagery. [Results] Both persistence and F/M amplitude ratios during motor imagery under maximum voluntary contractions of 10%, 30%, and 50% were significantly higher than that at rest. In addition, persistence, F/M amplitude ratio, and latency were similar during motor imagery under the three muscle contraction strengths. [Conclusion] Motor imagery under maximum voluntary contractions of 10%, 30%, and 50% can increase the excitability of spinal motor neurons. The results indicated that differences in muscle contraction strengths during motor imagery are not involved in changes in the excitability of spinal motor neurons.