The cortical silent period and amyotrophic lateral sclerosis

Area of Science:

• Neuroscience
• Neurology

Background:

• The cortical silent period (C-SP) reflects inhibitory processes in the motor cortex.
• Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting motor neurons.

Purpose of the Study:

• To investigate cortical silent period (C-SP) characteristics in patients with amyotrophic lateral sclerosis (ALS) compared to healthy controls.
• To explore the relationship between C-SP parameters and disease duration in ALS.

Main Methods:

• Transcranial magnetic stimulation (TMS) was used to elicit the C-SP in 25 normal subjects and 19 ALS patients.
• Stimulus intensity (SI)-dependency and age-dependency of C-SP were analyzed.
• Comparisons were made between normal and ALS groups regarding C-SP means, maximums, ranges, and cortical stimulation thresholds.

Main Results:

• Cortical silent period (C-SP) was stimulus intensity (SI)-dependent in both groups (mean r2 = 0.89).
• C-SP range was age-dependent in normals but not in ALS patients.
• No significant differences were found in C-SP means, maximums, ranges, or cortical stimulation thresholds between normal and ALS groups.
• A significant linear relationship was observed between maximum C-SP and ALS disease duration (P = 0.002).
• Maximum C-SP was shorter in the early stages of ALS.

Conclusions:

• Reduced cortical inhibition, indicated by a shorter maximum C-SP, is present early in amyotrophic lateral sclerosis (ALS).
• This early reduction in inhibition may be associated with glutamate-induced corticomotoneuronal excitotoxicity.
• C-SP alterations may serve as a potential biomarker for early disease stages in ALS.