Direct interrogation of cortical interneuron circuits in amyotrophic lateral sclerosis
Mehdi A J van den Bos1,2, Parvathi Menon1,2, Nathan Pavey1,2
1Brain and Nerve Research Centre, Concord Clinical School, The University of Sydney, Sydney, NSW 2139, Australia.
Brain : a Journal of Neurology
|October 10, 2024
Summary
Amyotrophic lateral sclerosis (ALS) involves cortical hyperexcitability due to GABAergic dysfunction. New TMS-EEG methods reveal localized motor cortex GABAergic circuit deficits in ALS patients, correlating with disease severity.
Area of Science:
- Neuroscience
- Neurology
- Biomedical Engineering
Background:
- Cortical hyperexcitability is a key feature in amyotrophic lateral sclerosis (ALS).
- This hyperexcitability is thought to involve complex interactions within cortical interneurons.
- Directly measuring cortical interneuron function has been a technological challenge.
Purpose of the Study:
- To investigate GABAergic dysfunction in ALS using a novel technological approach.
- To examine motor cortex output and interneuron function in ALS patients compared to controls.
- To correlate neurophysiological findings with clinical measures of disease severity and duration.
Main Methods:
- Combined transcranial magnetic stimulation (TMS) with advanced electroencephalography (EEG) to record transcranial evoked potentials (TEPs).
- Applied single-pulse and inhibitory paired-pulse TMS over the primary motor cortex in 21 ALS patients and healthy controls.
- Analyzed specific TEP components (N44, N100, P60, P190) and their changes in response to TMS paradigms.
Main Results:
- ALS patients showed reduced N100 and increased P190 components in single-pulse TEPs, indicating GABAergic dysfunction.
- Paired-pulse TMS revealed reduced inhibition in ALS patients (affecting P60 and N100), consistent with GABAA-ergic circuit dysfunction.
- The N44 component correlated with muscle weakness, and reduced N100 inhibition correlated with longer disease duration.
Conclusions:
- Novel TMS-EEG technology successfully identified localized GABAergic circuit dysfunction in the motor cortex of ALS patients.
- Findings support the hypothesis that cortical hyperexcitability in ALS is mediated by cortical disinhibition.
- The identified GABAergic dysfunction has pathophysiological significance, correlating with clinical disability and disease progression in ALS.
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