Intermittent bilateral coherence in physiological and essential hand tremor

Area of Science:

• Neuroscience
• Biophysics
• Movement Disorders

Background:

• Bilateral coherence, the synchronized oscillation between two limbs, is a key aspect of motor control and can be altered in tremor disorders.
• Understanding the temporal dynamics of this synchronization is crucial for differentiating tremor types and identifying underlying mechanisms.

Purpose of the Study:

• To investigate the prevalence and temporal characteristics of bilateral coherence in physiological tremor (PT) and essential tremor (ET).
• To explore the relationship between hand tremor coherence and other physiological rhythms, such as ballistocardiac activity.

Main Methods:

• Utilized triaxial accelerometry to record hand tremor in healthy subjects and patients with ET.
• Applied spectral and wavelet coherence analyses to quantify bilateral hand synchronization.
• Employed partial coherence analysis to assess the link between hand tremor and chest wall acceleration.

Main Results:

• Significant bilateral coherence was observed in the majority of both PT and ET subjects.
• In PT, coherence was most prevalent during resting hand positions (97%), while in ET, it was comparable in resting (54%) and postural (49%-57%) positions.
• Coherent epochs in both groups were intermittent, with PT coherence at the main tremor frequency linked to the ballistocardiac rhythm.

Conclusions:

• Hand oscillations are intermittently synchronized in both PT and ET.
• Postural PT coherence may result from transient entrainment of hand oscillations to ballistocardiac forcing.
• Bilateral hand coherence serves as a sensitive indicator of synchronizing influences on tremor oscillators.