Changes in cerebellar output abnormally modulate cortical myoclonus sensorimotor hyperexcitability

Area of Science:

• Neuroscience
• Clinical Neurology
• Neurophysiology

Background:

• Cortical myoclonus involves abnormal sensorimotor cortex neuronal discharges.
• Cerebellar dysfunction may lead to motor cortex hyperexcitability via cerebello-thalamo-cortical pathways.

Purpose of the Study:

• To investigate the effect of anodal cerebellar transcranial direct current stimulation (ctDCS) on sensorimotor cortex excitability in cortical myoclonus.
• To test the hypothesis that cerebellar stimulation can modulate cerebello-thalamo-cortical pathways to reduce hyperexcitability in cortical myoclonus.

Main Methods:

• Applied anodal cerebellar ctDCS for 20 minutes to 10 cortical myoclonus patients and 10 healthy controls.
• Assessed sensorimotor cortex excitability using somatosensory evoked potentials (SEPs), long-latency reflexes, and short-interval intracortical inhibition (SICI).
• Recorded myoclonus severity via surface electromyography (EMG).

Main Results:

• Anodal cerebellar ctDCS did not affect measures in healthy controls.
• In patients, anodal cerebellar ctDCS significantly increased SEP cortical components and long-latency reflexes, and decreased SICI.
• A trend towards worsening of myoclonus was observed post-stimulation, particularly in patients with giant SEPs.

Conclusions:

• Anodal cerebellar ctDCS paradoxically facilitates sensorimotor cortex excitability in cortical myoclonus.
• This suggests dysfunctional cerebello-thalamo-cortical pathways and abnormal homeostatic plasticity in the sensorimotor cortex.
• The cerebellum's role in cortical myoclonus pathophysiology is highlighted, suggesting potential new therapeutic targets.