Objective: Patients with Essential tremor (ET) may face challenges performing tasks of daily living due to the presence of tremor during action. A common strategy to aid task performance is to use two hands, which reportedly reduces tremor and makes many tasks of daily living more doable. However, the physiological mechanism that underlies this tremor reduction is unknown. Here we use electromyography (EMG) and accelerometry (ACC) to explore tremor characteristics when performing a task unimanually versus bimanually.

Background: ET is the most common movement disorder, affecting limbs during movements of action or posturing.  The tremor associated with ET has a frequency of 4-12 Hz, with the main component being driven by a central oscillator and a possible secondary component arising from limb mechanics and/or stretch reflex pathway.

Method: Ten right-handed ET patients participated in the study. Inclusion criteria included diagnosis of ET, a clear central component during a tremor study, and a score of at least 2 in one hand and 1.5 in the other during posture, wingbeat, and/or finger to nose components of The Essential Tremor Rating Scale.

EMG electrodes were attached bilaterally to the arm flexor and extensor muscles and accelerometers were attached to the back of patients’ hands. Recordings included holding a cup, wingbeat, and extending both arms up. For each posture, data was collected while holding the posture with a single hand and bimanually with the hands touching.

Results: A time frequency analysis was performed for all recordings to calculate the power at the tremor frequency. Overall, we report that during cup holding and wingbeat, the power of the tremor recorded from the ACC significantly decreased on the right side but not the left. In contrast, we find that the power calculated from the EMG data significantly decreased on the left side, but not the right. These changes were not present for the position with the arms up and extended.
Subsequent analysis revealed a significant increase in coherence between the left and right ACC and left and right EMG traces when the hands were touching. There was also a significant reduction in coherence between right EMG/ACC with hands touching, but no change in the left side.

Conclusion: These findings suggest that bimanual task performance does change the physiological characteristics of the tremor.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/exploring-the-physiological-mechanisms-of-tremor-reduction-with-bimanual-performance-in-essential-tremor-patients/