Voluntary Tremor Suppression in Parkinson's Disease

Abstract

Parkinson’s disease (PD) is a common degenerative neurological disorder, and resting tremor is one of the main symptoms of this disease. It has been observed that some patients with Parkinsonian rest tremor are able to suppress their tremor voluntarily with mental concentration or by focusing attention on the affected limb. This process is not well understood and this study aims to describe and assess voluntary tremor suppression in patients with PD, as well as to identify the critical cortical or subcortical regions activated during this process. Methods: Nine participants with tremor-dominant PD were recruited for this study. These patients had unilateral rest tremors of the upper limb and were able to consciously stop their tremor for a period of time. Each patient was assessed using the Unified Parkinson’s Disease Rating Scale (UPDRS), movement tracking and functional imaging. Physical characteristics of the tremor such as amplitude and frequency were measured using a 3-D Polhemus Liberty electromagnetic movement tracking in the MoVELab. Functional imaging was undertaken using functional magnetic resonance imaging (fMRI) in a 3.0 Tesla scanner, with functional data collected with a standard T2 weighted MRI sequence along with T1 weighted 3-D anatomical data. Results: The extent of voluntary tremor suppression differed between the participants with some being able to suppress reliably for long periods of time, and others unable to do so consistently. Participants had slight to moderate tremors according to the UPDRS. The majority of participants described their method of suppression as concentrating on the affected limb and/or focusing on relaxing the limb. Movement tracking confirmed what was observed, with variation in tremor amplitude, and the extent of suppression. FMRI showed differing areas of activation involved in tremor suppression amongst the participants. Activated areas were generally contralateral to the tremor, and were widespread, including parts of the primary motor cortex, superior parietal lobule, supramarginal gyrus and middle frontal gyrus. Conclusion: This study was the first attempt at describing the process of voluntary tremor suppression in PD. The differing methods the participants used to suppress their tremor were recorded and described, and objective measures of the suppression taken. Functional imaging revealed a number of areas involved in tremor suppression.