Long-interval intracortical inhibition is similar in people with and without amyotrophic lateral sclerosis.

Overview

1. Discipline of Physiology, School of Medicine, Trinity Biomedical Sciences Institute, Trinity College Dublin, The University of Dublin, Dublin D02 R590, Ireland
2. Academic Unit of Neurology, School of Medicine, Trinity Biomedical Sciences Institute, Trinity College Dublin, The University of Dublin, Dublin D02 R590, Ireland
3. Department of Neurology, Beaumont Hospital, Dublin D09 V2N0, Ireland
4. Department of Orthopaedic Surgery, Otto-von-Guericke University, 39120 Magdeburg, Germany
5. Trinity College Institute of Neuroscience and School of Psychology, Trinity College Dublin, The University of Dublin, Dublin D02 R590, Ireland

Abstract

Long-interval intracortical inhibition, measured using transcranial magnetic stimulation, provides a non-invasive measure of spinal inhibition at interstimulus intervals below 100 ms and of GABA-B-mediated motor cortical inhibition at interstimulus intervals of 100–200 ms. To date, only a few small studies have investigated if long-interval intracortical inhibition is affected in amyotrophic lateral sclerosis. None have employed threshold tracking protocols or investigated multiple induced current directions. In this study, we aimed to determine if long-interval intracortical inhibition (i) differs between people with amyotrophic lateral sclerosis and healthy controls; (ii) relates to motor symptom severity, disease duration or survival time in those with amyotrophic lateral sclerosis; or (iii) relates to intracortical facilitation or short-interval intracortical inhibition. Employing automated threshold tracking during paired-pulse transcranial magnetic stimulation of the precentral gyrus, long-interval intracortical inhibition was recorded in 30 people with amyotrophic lateral sclerosis [9 female, 21 male, median (range) age: 63.5 (41–79) years] and 45 healthy controls [16 female, 29 male, median (range) age: 57 (34–76) years]. Long-interval intracortical inhibition was recorded with interstimulus intervals of 50, 100, 150 and 200 ms using posterior-to-anterior induced current (LICIPA), and with interstimulus intervals of 150 and 200 ms using anterior-to-posterior induced current (LICIAP). In subcohorts of both healthy controls and people with amyotrophic lateral sclerosis, short-interval intracortical inhibition was recorded with interstimulus intervals of 1 and 3 ms using posterior-to-anterior induced current and 3 ms using anterior-to-posterior current. Intracortical facilitation was recorded with an interstimulus interval of 10 ms using posterior-to-anterior induced current. No differences were found between those with and without amyotrophic lateral sclerosis in long-interval intracortical inhibition magnitude (P ≥ 0.44, Hedge’s g ≤ 0.14) or in the interstimulus interval at which maximal long-interval intracortical inhibition occurs (P = 0.68, χ2 = 1.5). In those with amyotrophic lateral sclerosis, no statistically significant correlations were identified between long-interval intracortical inhibition measures and disease duration or functional rating scale scores. Statistically significant positive correlations were observed between LICIPA recorded with 100 and 150 ms interstimulus intervals, and between LICIPA recorded with 150 and 200 ms interstimulus intervals, but not between LICIPA and LICIAP measures or between long-interval intracortical inhibition and short-interval intracortical inhibition or intracortical facilitation. Our findings indicate that disinhibition manifested in this disease is primarily not mediated via changes in the cortical GABA-Bergic or spinal circuitry which underpins long-interval intracortical inhibition measures. As LICIPA and LICIAP measures show minimal covariation, it is possible that these measures are underpinned by distinct aspects of motor cortical inhibition.

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Data availability

Anonymized data will be made available upon reasonable request to the corresponding author. A manual form of the maximum likelihood PEST protocol employed for threshold tracking is available in the TMS Motor Threshold Assessment Tool, MTAT 2.0, available at: https://www.clinicalresearcher.org/software.htm.

Reproduced under the paper's license (CC BY), from the paper cited above.

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Recorded: type, language, journal, volume, issue, pages, dates, 9 authors, 5 keywords, 5 funders, 59 references.

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This paper

McMackin, R., Tadjine, Y., Suleyman, N., Woods, E., Plaitano, S., Fasano, A., Awiszus, F., Hardiman, O., & Carson, R. G. (2026). Long-interval intracortical inhibition is similar in people with and without amyotrophic lateral sclerosis. Brain communications, 8(2), fcag091. https://doi.org/10.1093/braincomms/fcag091

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