Essential tremor accentuates the pattern of tremor-band coherence between upper limb muscles

Journal article, 2023

Although essential tremor (ET) is one of the most common movement disorders, current treatment options are relatively limited. Peripheral tremor suppression methods have shown potential, but we do not currently know which muscles are most responsible for patients' tremor, making it difficult to optimize suppression methods. The purpose of this study was to quantify the relation-ships between the tremorogenic activity in muscles throughout the upper limb. Muscle activity was recorded from the 15 major superficial upper limb muscles in 24 subjects with ET while they held various postures or made upper limb movements. We cal-culated the coherence in the tremor band (4-12 Hz) between the activity of all muscle pairs and the time-varying phase differ-ence between sufficiently coherent muscle pairs. Overall, the observed pattern somewhat mirrored functional relationships: agonistic muscle pairs were most coherent and in phase, whereas antagonist and unrelated muscle pairs exhibited less coher-ence and were either consistently in phase, consistently antiphase, consistently out of phase (unrelated pairs only), or else incon-sistent. Patients exhibited significantly more coherence than control subjects (P < 0.001) in the vast majority of muscle pairs (95 of 105). Furthermore, differences between patients and control subjects were most pronounced among agonists; thus, the coher-ence pattern existing in control subjects was accentuated in patients with ET. We conclude that tremor-band activity is broadly distributed among the muscles of the upper limb, challenging efforts to determine which muscles are most responsible for a patient's tremor.