Objective: To investigate the brain plasticity for controlling the dominant and non-dominant hand muscles and reach-to-grasp (RTG) functions in Parkinson’s disease (PD).

Background: Previous studies have shown shorten cortical silent period (CSP) in PD. This represents the defective inhibitory system. The CSP and motor evoked potential (MEP) amplitude were measured during isometric contraction of the hand muscle. Among those studies, only one investigated the change of MEP amplitude at rest and it was measured on the dominant hemisphere of one muscle, i.e. abductor pollicis brevis. The MEP amplitude measured at rest represents the integrity of the corticospinal tract. In daily life, activity like RTG involves the muscles of wrist and hand muscles. Therefore, it is important to investigate the integrity of corticospinal system controlling those muscles of each hand.

Methods: The PDs and age-matched non-disabled controls were recruited.  The brain plasticity was represented by resting motor threshold (rMT), the peak-to-peak amplitude of MEP and the CSP. The target muscles were extensor digitorum (ED), first dorsal interosseous (FDI), and abductor pollicis brevis (APB) muscles. The RTG performances were measured by the time of the Woft Motor Function test to complete lifting a can and stacking checkers.

Results: Ten PD (aged 46-72 years) and 10 age-matched controls (aged 47-71 years) participated. All of them were right hand dominant. In PD, the Hoehn and Yahr scale were I (n=3), II (n=6), and III n=1). The CSP duration was significantly shorter than that of the control. In contrast, there were no group differences in rMT of ED, FDI and APB of both hands. Different pattern was observed for the MEP. There were no group differences for the EDC and FDI muscles. Compared to the controls, the MEP of APB muscle decreased in the right hand and increased in the left hand of PD. Behaviorally, the PD completed the RTG tasks with significantly longer time than the controls.

Conclusions: Our findings showed the deficits of RTG performance in PD. Consistent with the previous study, we demonstrated the impaired inhibitory system evidenced by the CSP. Importantly, this is the first study to show the muscle specific pattern of the integrity of the corticospinal tract in PD. The findings of MEP suggest that for both hands, PD has intact integrity of corticospinal tract controlling ED and FDI muscles with the impaired integrity controlling APB muscle.

References: 1.Valls-Solé J, Pascual-Leone A, Brasil-Neto JP, Cammarota A, McShane L, Hallett M. Abnormal facilitation of the response to transcranial magnetic stimulation in patients with Parkinson’s disease. Neurology 1994; 44:735-741.

2. Wu, AD., Petzinger GM, Lin Chien-Ho J., Kung M, Fisher B. Asymmetric corticomotor excitability correlations in early Parkinson’s disease. Movement Disorders 2007; 22(11): 1587–1593.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-brain-plasticity-for-controlling-reach-to-grasp-functions-of-parkinsons-disease/