Magnetic stimulation in Alzheimer's disease

Area of Science:

• Neuroscience
• Neurology
• Clinical Medicine

Background:

• Alzheimer's disease (AD) is a leading cause of dementia, often presenting with motor abnormalities.
• The underlying neurophysiological mechanisms of these motor symptoms in AD are not fully understood.

Purpose of the Study:

• To investigate motor cortex excitability in Alzheimer's disease patients using transcranial magnetic stimulation (TMS).
• To test the hypothesis that altered motor cortex excitability contributes to motor abnormalities in AD.

Main Methods:

• Transcranial magnetic stimulation (TMS) was employed to assess motor evoked potential (MEP) thresholds.
• Fourteen patients with mild to moderate Alzheimer's disease were compared with 11 age, height, and sex-matched healthy controls.
• Spinal motor neuron excitability was evaluated using F/M and H/M wave amplitude ratios.

Main Results:

• AD patients demonstrated significantly lower motor evoked potential thresholds in both left and right motor cortices compared to controls (P < 0.05).
• No significant differences in interhemispheric threshold differences were observed between groups.
• Spinal motor neuron excitability remained unchanged, supporting increased cortical excitability as the primary finding.

Conclusions:

• Alzheimer's disease is associated with increased excitability in the motor cortex.
• This heightened excitability may stem from degeneration of inhibitory GABAergic terminals or postsynaptic changes in GABAA receptors.
• Understanding this increased motor cortex excitability is crucial for explaining seizures and myoclonus in Alzheimer's disease.