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Publicação
Reducing Motor Evoked Potential amplitude variability through normalization
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Orientador(es)
Resumo(s)
Transcranial Magnetic Stimulation (TMS) has several different applications, including in vivo assessment of motor cortical excitability in humans. When applied over the motor cortex, TMS single-pulses
result 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 their acquisition, and their inherent high variability have led to constraints in reproducibility. Normalization has been used to reduce variability of EMG measurements.
Albeit being a standard practice to allow between-subject comparisons in EMG research, its effect on
MEP variability has not been explored. In this study we aim to explore the impact of different normalization methods in MEP amplitude variability.
After validating our in-house built EMG acquisition system, Maximal Voluntary Isometric Contractions (MVICs) and MEPs were collected from 47 healthy volunteers. Four different strategies were used
in MEP normalization: two based on external references and two based on internal references. Bootstrapping was used to define distributions of coefficients of variation (CV) for each normalization method.
Specifically, iterative re-sampling of 30 MEPs per subject, repeated 5000 times, was performed and a
distribution of CVs per method was obtained, allowing for statistical comparison of between-subject
variability. A retest session was conducted to assess the impact of normalization on within-subject variability of MEP amplitude measurements, using intra-class correlation coefficients (ICC).
While normalization using external references did not reduce the CV, internal reference normalization resulted in a reduction of approximately 67% of between-subject variability. Normalization did not
reduce within subject variability as measured by the ICCs.
Our findings suggest that internal reference normalization reduces between-subject variability and
has a minimal impact on within-subject variability. Additional research is necessary to further improve
internal reference normalization methods towards potential use of MEPs as biomarkers of neuropsychiatric disorders.
Descrição
Tese de mestrado integrado, Engenharia Biomédica e Biofísica (Sinais e Imagens Médicas), 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Estimulação Magnética Transcraniana Potenciais Evocados Motores Normalização Variabilidade Electromiografia Teses de mestrado - 2023