Effect of vibrotactile stimulation on Parkinson*s tremor * an explorative study

Parkinson*s disease (PD) is the second most common neurodegenerative disease,
of which tremor is a common and highly burdensome symptom. The pathophysiology
of tremor involves a cerebral network that consists of basal ganglia and a
cerebello-thalamo-cortical motor circuit. Emerging evidence suggest that
somatosensory input from the tremulous limb to the brain may influence this
network. Specifically, tremor-related activity was observed in primary and
secondary somatosensory cortex and thalamic cells that are involved in tremor
are also responsive to somatosensory stimulation. Somatosensory afferents may
thus play a role in tremor pathophysiology and could therefore be used as
treatment target. Here, we will test this hypothesis by investigating the
effect of modulating somatosensory input (with vibrotactile stimulation) on
tremor severity.

The primary objective is to test whether rhythmic somatosensory input
(vibrotactile stimulation at tremor frequency) reduces tremor power of
Parkinson*s tremor, as compared to other vibrotactile stimulation settings
(continuous stimulation, stimulation at 1.5 times tremor frequency, sham
stimulation). As secondary objectives, we will test whether the effect of
vibrotactile stimulation on tremor power depends on the context in which tremor
occurs (rest, cognitive coactivation, posture) and whether vibrotactile
stimulation has an effect on two other common PD symptoms: impaired gait and
bradykinesia.

Cross-sectional exploratory intervention study.

The intervention involves subtle mechanical vibrations (vibrotactile
stimulation) on the wrist or ankles. This is a non-invasive and painless way to
provide somatosensory stimuli, in a continuous (80Hz) or rhythmic fashion
(brief bursts of 80 Hz at tremor or step frequency).

The load on patients consists of the time spent on this project, and
potentially a temporary worsening of symptoms caused by withholding medication.
Patients will arrive in a practically defined OFF state, i.e. at least 12 hours
after having taken their last dopaminergic medication. At the end of the
measurement, they will resume their normal medication regime. All measurements
are non-invasive, painless, and without nuclear radiation. Individual
participants do not directly benefit from participation. However, we expect
that this study will provide mechanistic insights into if and how somatosensory
(vibro-tactile) afferents influence the cerebral tremor circuit in Parkinson*s
disease, and may provide a solid basis for designing further clinical treatment
studies.