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Faro Viana F, Cotovio G, da Silva DR, Seybert C, Pereira P, Silva A, Carvalho F, Oliveira-Maia AJ. Reducing motor evoked potential amplitude variability through normalization. Front Psychiatry 2024; 15:1279072. [PMID: 38356910 PMCID: PMC10864444 DOI: 10.3389/fpsyt.2024.1279072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 01/04/2024] [Indexed: 02/16/2024] Open
Abstract
BackgroundTranscranial Magnetic Stimulation (TMS) is used for in vivo assessment of human motor cortical excitability, with application of TMS pulses over the motor cortex resulting in muscle responses that can be recorded with electromyography (EMG) as Motor Evoked Potentials (MEPs). These have been widely explored as potential biomarkers for neuropsychiatric disorders but methodological heterogeneity in acquisition, and inherent high variability, have led to constraints in reproducibility. Normalization, consisting in scaling the signal of interest to a known and repeatable measurement, reduces variability and is standard practice for between-subject comparisons of EMG. The effect of normalization on variability of MEP amplitude has not yet been explored and was assessed here using several methods.MethodsThree maximal voluntary isometric contractions (MVICs) and 40 MEPs were collected from the right hand in healthy volunteers, with a retest session conducted 4 to 8 weeks later. MEP amplitude was normalized using either external references (MVICs) or internal references (extreme MEPs). Iterative re-sampling of 30 normalized MEPs per subject was repeated 5,000 times to define, for each normalization method, distributions for between-subject coefficients of variation (CV) of the mean MEP amplitude. Intra-class correlation coefficients (ICC) were used to assess the impact of normalization on test–retest stability of MEP amplitude measurements.ResultsIn the absence of normalization, MEPs collected from the right hand of 47 healthy volunteers were within reported values regarding between-subject variability (95% confidence intervals for the CV: [1.0567,1.0577]) and showed good temporal stability (ICC = 0.77). Internal reference normalization substantially reduced between-subject variability, by values of up to 64%, while external reference normalization had no impact or increased between-subject variability. Normalization with the smallest references reduced test–retest stability, with use of the largest references resulting in slight reduction or improvement of ICCs. Internal reference normalization using the largest MEPs was found to be robust to several sensitivity analyses.ConclusionInternal, but not external, reference normalization reduces between-subject variability of MEP amplitude, and has a minimal impact on within-subject variability when conducted with the largest references. Additional research is necessary to further validate these normalization methods toward potential use of MEPs as biomarkers of neuropsychiatric disorders.
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Affiliation(s)
- Francisco Faro Viana
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
- Champalimaud Clinical Centre, Champalimaud Foundation, Lisbon, Portugal
| | - Gonçalo Cotovio
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
- Champalimaud Clinical Centre, Champalimaud Foundation, Lisbon, Portugal
- NOVA Medical School, Faculdade de Ciências Médicas, NMS, FCM, Universidade NOVA de Lisboa, Lisbon, Portugal
- Department of Psychiatry and Mental Health, Centro Hospitalar de Lisboa Ocidental, Lisbon, Portugal
| | - Daniel Rodrigues da Silva
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
- Champalimaud Clinical Centre, Champalimaud Foundation, Lisbon, Portugal
| | - Carolina Seybert
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
- Champalimaud Clinical Centre, Champalimaud Foundation, Lisbon, Portugal
| | - Patrícia Pereira
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
- Champalimaud Clinical Centre, Champalimaud Foundation, Lisbon, Portugal
- Portuguese Red Cross Health School, Lisbon, Portugal
| | - Artur Silva
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
| | - Filipe Carvalho
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
| | - Albino J. Oliveira-Maia
- Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal
- Champalimaud Clinical Centre, Champalimaud Foundation, Lisbon, Portugal
- NOVA Medical School, Faculdade de Ciências Médicas, NMS, FCM, Universidade NOVA de Lisboa, Lisbon, Portugal
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Royer N, Coates K, Aboodarda SJ, Camdessanché JP, Millet GY. How is neuromuscular fatigability affected by perceived fatigue and disability in people with multiple sclerosis? Front Neurol 2022; 13:983643. [DOI: 10.3389/fneur.2022.983643] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Accepted: 09/23/2022] [Indexed: 11/13/2022] Open
Abstract
Whereas fatigue is recognized to be the main complaint of patients with multiple sclerosis (PwMS), its etiology, and particularly the role of resistance to fatigability and its interplay with disability level, remains unclear. The purposes of this review were to (i) clarify the relationship between fatigue/disability and neuromuscular performance in PwMS and (ii) review the corticospinal and muscular mechanisms of voluntary muscle contraction that are altered by multiple sclerosis, and how they may be influenced by disability level or fatigue. Neuromuscular function at rest and during exercise are more susceptible to impairement, due to deficits in voluntary activation, when the disability is greater. Fatigue level is related to resistance to fatigability but not to neuromuscular function at rest. Neurophysiological parameters related to signal transmission such as central motor conduction time, motor evoked potentials amplitude and latency are affected by disability and fatigue levels but their relative role in the impaired production of torque remain unclear. Nonetheless, cortical reorganization represents the most likely explanation for the heightened fatigability during exercise for highly fatigued and/or disabled PwMS. Further research is needed to decipher how the fatigue and disability could influence fatigability for an ecological task, especially at the corticospinal level.
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