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. 2020 Mar;8(6):e14393.
doi: 10.14814/phy2.14393.

Differential Neural Coordination of Bilateral Hand and Finger Movements

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Free PMC article

Differential Neural Coordination of Bilateral Hand and Finger Movements

Paolo Caldelari et al. Physiol Rep. .
Free PMC article

Abstract

Cooperative hand movements (e.g., opening a bottle) require a close coordination of the hands. This is reflected in a neural coupling between the two sides. The aim of this study was to investigate in how far neural coupling is present not only during bilateral hand but also during bilateral finger movements. For this purpose unilateral mechanical and electrical nerve stimuli were delivered during bilateral sequentially and synchronously performed finger movements on a keyboard and, for comparison, during bilateral hand flexion movements. Electromyographic (EMG) activity and reflex responses in forearm flexor and extensor muscles of both sides were recorded and analyzed. Confounding EMG activity related to hand movements during the finger task was limited by wrist fixating braces. During the hand flexion task, complex reflex responses appeared in the forearm muscles of both sides to unilateral stimulation of the ulnar nerve (mean latency 57 ms), reflecting neural coupling between the two hands. In contrast, during the bilateral finger movement task, unilateral electrical nerve or mechanical stimulation of the right index finger was followed by dominant ipsilateral reflex responses (latency 45 and 58 ms, respectively). The results indicate that in contrast to the coupled hand movements, finger movements may not be coupled but can move independently on each side. Functionally this makes sense because during most activities of daily living, a close cooperation of the hands but not of individual fingers is needed. This independence of individual finger movements may rely on strong, specific, contralateral cortico-motoneuronal control.

Keywords: bilateral hand/finger movements; contralateral reflex activity; forearm muscle activity; neural coupling.

Conflict of interest statement

The authors declare no competing interests.

Figures

FIGURE 1
FIGURE 1
Illustration of the experimental tasks and conditions. The experiment consisted of two tasks. One task, consisted of bilateral synchronously performed sequential finger tapping movements on a keyboard, included two conditions. These conditions differed in the type of randomly applied dummy or experimental stimuli which were released when the prepared key was touched by the right index finger. In condition a. ‘mechanical’: stimulation an increased resistive force of the key occurred (upward arrow in bottom left inset) against the downward movement of the key by the index finger. During the second condition b. ‘electrical’: the initiation of key press by the right index finger randomly triggered the delivery of an electrical stimulus to the right ulnar nerve. The second task c. consisted of bilateral hand flexion movements while holding dumbbells (load: 0.5 kg). Electrical stimuli to the ulnar nerve were randomly applied during the rising phase of the movements
FIGURE 2
FIGURE 2
Block diagram illustrating the technical design of a single keyboard key which was prepared for mechanical finger stimuli and for triggering mechanical and electrical stimuli. The custom‐built setup was placed under the key which was to be pressed by the right index finger. The design enabled the random delivery of (a): mechanical stimuli, (b): stimuli for triggering the EMG responses to mechanical/electrical stimuli. To implement these functions an Arduino microcontroller was used. The C‐code used to program the Arduino microcontroller was compiled with the Arduino IDE Software. The onset of the downward movement of the key activated the photoelectric switch which then started the random generator controlled by the Arduino. The random generator released mechanical/ electrical stimuli or no stimuli depending on the experimental condition. For the mechanical perturbation, the servo pressed the cantilever against the bottom of the key to return the key after the initial downward movement of the key by the subject's right index finger. For electrical stimuli, the TTL‐pulse was used to trigger electrical stimuli delivered by a Digitimer DS5 and triggering of the EMG responses for electrical or dummy stimuli. C‐code: C programming language used by Arduino Uno microcontroller; USB: Universal Serial Bus; interface between laptop and Arduino; TTL pulse: Transistor Transistor Logic pulse (5 V) generated by Arduino; FSR: Force Sensing Resistor; sensor for the force measurement between cantilever and the key; Servo & PS: Interface between Arduino and the Actuator/Sensor unit. This interface had two functions: Steering the servo motor and reading of the PS (Photoelectric Switch) sensors
FIGURE 3
FIGURE 3
Bilateral forearm muscle EMG activity and reflex recordings of the two experimental conditions in the finger task (a: mechanical, b: electrical stimuli) and of the hand task (c) from one representative subject. Fifteen stimuli were applied in every condition. In (a) the averaged, rectified EMG recordings of the forearm flexors is shown together with the single trial and average (thick line) force signals after mechanical stimuli. In (b), responses of the extensors of both sides following electrical stimuli are illustrated. During the hand task (c) the flexor muscles were activated. Vertical dotted line indicates onset of stimulation; the gray areas reflect the EMG activity following dummy trials without stimuli
FIGURE 4
FIGURE 4
Grand averages of bilateral forearm muscle EMG activity with reflex responses of the two experimental conditions in the finger task (a, mechanical (n = 15 subjects) and b, electrical stimuli (n = 12 subjects)) and for comparison of the hand task (c, n = 13 subjects). Gray areas reflect the EMG activity in dummy trials without stimuli. The vertical lines indicate the windows used for the quantification of the reflex responses on both sides. In (a), the dotted line represents the averaged force signals after mechanical stimuli
FIGURE 5
FIGURE 5
(A) Quantified RMS values of reflex responses and background EMG (dummy trials) calculated for the time windows indicated in Figure 4. Dummy trials are represented by gray bars and experimental conditions by white bars. There was a significant difference between RMS values of both ipsilateral and contralateral reflex responses to mechanical (Aa; n = 15 subjects) and electrical (Ab; n = 12 subjects) stimuli for the finger task as well as for the hand task (Ac; n = 13 subjects) compared with the RMS of background EMG activity following dummy stimuli. (B) Absolute reflex responses for the ipsilateral and contralateral side: Mean absolute difference values were calculated as the absolute difference between reflex responses to mechanical (Aa) and electrical (Ab) stimuli for the finger task as well as for the hand task (Ac) and the background EMG activity in dummy trials. Ipsilateral reflex responses where larger than contralateral responses to unilateral (right side) mechanical (Ba) and electrical (Bb) stimuli in the finger movement task but not for the hand task (Bc). Ba; n = 15 subjects, Bb; n = 12 subjects, Bc; n = 13 subjects). Significant differences in (A) and (B) are indicated by one asterisk (p < .05), two asterisks (p < .01), or three asterisks (p < .001)

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References

    1. Bracewell R. M., Wing A. M., Soper H. M., & Clark K. G. (2003). Predictive and reactive co‐ordination of grip and load forces in bimanual lifting in man. European Journal of Neuroscience, 18, 2396–2402. 10.1046/j.1460-9568.2003.02944.x - DOI - PubMed
    1. Cole K. J., Gracco V. L., & Abbs J. H. (1984). Autogenic and nonautogenic sensorimotor actions in the control of multiarticulate hand movements. Experimental Brain Research, 56, 582–585. 10.1007/BF00238001 - DOI - PubMed
    1. Dietz V., Macauda G., Schrafl‐Altermatt M., Wirz M., Kloter E., & Michels L. (2015). Neural coupling of cooperative hand movements: A reflex and FMRI study. Cerebral Cortex, 25, 948–958. 10.1093/cercor/bht285 - DOI - PubMed
    1. Ejaz N., Xu J., Branscheidt M., Hertler B., Schambra H., Widmer M., … Diedrichsen J. (2018). Evidence for a subcortical origin of mirror movements after stroke: A longitudinal study. Brain, 141, 837–847. 10.1093/brain/awx384 - DOI - PMC - PubMed
    1. Evans A. L., Harrison L. M., & Stephens J. A. (1989). Task‐dependent changes in cutaneous reflexes recorded from various muscles controlling finger movement in man. Journal of Physiology, 418, 1–12. 10.1113/jphysiol.1989.sp017825 - DOI - PMC - PubMed

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