Interhemispheric and ipsilateral connections in Parkinson's disease: relation to mirror movements
Jie-Yuan Li1, Alberto J Espay, Carolyn A Gunraj
1Division of Neurology, Department of Medicine, Toronto Western Research Institute, University of Toronto, Toronto, Ontario, Canada.
Abstract:
Mirror movements (MM) occur in early, asymmetric Parkinson's disease (PD). To examine the pathophysiology of MM in PD, we studied 13 PD patients with MM (PD-MM), 7 PD patients without MM (PD-NM), and 14 normal subjects. Cross-correlogram did not detect common synaptic input to motoneuron pools innervating homologous hand muscles in PD-MM patients. Transcranial magnetic stimulation studies showed no significant difference in ipsilateral motor-evoked potentials between PD-MM patients and normal subjects. The MM side of PD-MM patients showed a slower increase in ipsilateral silent period area with higher level of muscle contraction than the non-MM side and normal subjects. There was less interhemispheric inhibition (IHI) at long interstimulus intervals of 20 to 50 ms in PD-MM than PD-NM. IHI reduced short interval intracortical inhibition in normal subjects and PD-NM, but not in PD-MM. IHI significantly increased intracortical facilitation in PD-MM and PD-NM patients, but not in normal subjects. Our results suggest that MM in PD is due to activation of the contralateral motor cortex. PD-MM patients had reduced transcallosal inhibitory effects on cortical output neurons and on intracortical inhibitory circuits compared to PD-NM patients and controls. These deficits in transcallosal inhibition may contribute to MM in PD patients.
Insights
Mirror movements in Parkinson's disease (PD) stem from contralateral motor cortex activation. Reduced transcallosal inhibition in PD patients with mirror movements (PD-MM) impacts cortical circuits.
Area of Science:
- Neuroscience
- Motor Control
- Clinical Neurology
Background:
- Mirror movements (MM) are observed in early Parkinson's disease (PD), particularly in asymmetric cases.
- The underlying pathophysiology of MM in PD remains incompletely understood.
Purpose of the Study:
- To investigate the neural mechanisms contributing to mirror movements in Parkinson's disease.
- To compare corticospinal excitability and interhemispheric inhibition between PD patients with and without MM, and healthy controls.
Main Methods:
- Studied 13 PD patients with MM (PD-MM), 7 PD patients without MM (PD-NM), and 14 healthy controls.
- Utilized cross-correlogram analysis to assess synaptic input to motoneurons.
- Employed transcranial magnetic stimulation (TMS) to evaluate ipsilateral motor-evoked potentials, silent periods, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF).
Main Results:
- No common synaptic input detected in PD-MM motoneurons.
- MM side showed altered silent period dynamics during muscle contraction.
- Reduced interhemispheric inhibition (IHI) at long intervals observed in PD-MM compared to PD-NM.
- IHI failed to modulate SICI in PD-MM, unlike in controls and PD-NM.
- IHI increased ICF in PD-MM and PD-NM, but not in controls.
Conclusions:
- Mirror movements in PD are likely caused by contralateral motor cortex activation.
- PD-MM patients exhibit diminished transcallosal inhibition affecting cortical output and inhibitory circuits.
- Deficits in transcallosal inhibition may be a key factor contributing to MM in Parkinson's disease.
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