Volitional Suppression of Parkinsonian Resting Tremor

Abstract

Background We have observed in the clinic that a number of patients with Parkinson's disease (PD) can suppress their tremor at will for brief periods, by conscious mental processes. To our knowledge, the ability to consciously diminish one's resting tremor has not yet been reported nor assessed quantitatively. Objective To provide the first detailed systematic investigation of the phenomenon of voluntary tremor suppression in PD. Methods We examined changes in tremor characteristics during voluntary tremor suppression in 37 PD patients (on medication) presenting with rest tremor in their upper limb. We measured tremor oscillations with a triaxis accelerometer on the index finger of the most‐affected hand (n = 27). With surface electromyography (EMG), we measured changes in neuromuscular activity of the forearm flexor digitorum superficialis and extensor digitorum muscles (n = 15). Participants completed four 1‐minute trials, consisting of alternating consecutive 30‐second periods of resting tremor and 30‐second periods of attempted tremor suppression. Results Bayesian multilevel modeling revealed that attempted voluntary tremor suppression did indeed reduce tremor amplitude (peak power) of the acceleration signal and increased tremor frequency of the acceleration and EMG signals. Relative EMG power in the 3‐ to 8‐Hz tremor band was also smaller. Tremor suppression was not by enhanced voluntary contraction of the relevant muscle pairs. Conclusions We present novel empirical evidence that PD resting tremor can be suppressed by an act of will, as evidenced by significant modulation of key neurophysiological tremor characteristics. These data highlight that it is possible to exert significant conscious control over parkinsonian resting tremor.

Clinical neurophysiology of Parkinson’s disease and parkinsonism

“…PD rest tremor typically increases during cognitive tasks or motor coactivation, e.g., counting or tapping with the contralateral hand, and this can be used by clinicians to bring out the tremor in the clinic ( Dirkx et al, 2020 ). PD tremor is very sensitive to stress, and it can be reduced with stress-reducing interventions such as mindfulness ( van der Heide et al, 2021 ) and relaxation exercises ( Blakemore et al, 2019 ). Patients with PD may also manifest tremor in the cranio-cervical area, including chin, tongue, and voice tremor.…”

Variability of Movement Disorders: The Influence of Sensation, Action, Cognition, and Emotions

“…75 This is associated with reduced amplitude and increased frequency of the tremor, highlighting the dissociation between the tremor oscillator and the cerebello-thalamocortical circuits controlling tremor amplitude. 76 Half of patients with chorea and 20% of patients with dystonia can also voluntarily reduce their movements. 75,77 Tics are the prototypical hyperkinetic movement disorders that may be suppressed voluntarily.…”

“…Patients with parkinsonian tremor, as opposed to essential tremor, are often capable of partial or complete suppression of their tremor purely by an act of will, if they are allowed to concentrate on this task 75 . This is associated with reduced amplitude and increased frequency of the tremor, highlighting the dissociation between the tremor oscillator and the cerebello‐thalamocortical circuits controlling tremor amplitude 76 …”