Alexandre Legros | Western University Canada (original) (raw)

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Papers by Alexandre Legros

Brain Stimulation, 2019

Objective: Investigate the effects of a bilateral TMS treatment protocol in patients with unipola... more Objective: Investigate the effects of a bilateral TMS treatment protocol in patients with unipolar refractory major depression with comorbid anxiety. Background: Some studies have suggested that TBS has a similar or better effect in the treatment of depression compared to more conventional TMS protocols. It has also been postulated that right side low frequency protocols have a better capacity to improve the symptoms of anxiety and, potentially, improve the overall antidepressant response. Design/Methods: A total of 32 adults diagnosed with refractory major depression were treated at the Instituto de Neuroestimulaci on de Lima (Peru) with 20-25 sessions of TMS. All patients met criteria for non-psychotic unipolar depression as determined by the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I) assessment and their current medications were maintained during the study. The bilateral treatment applied consisted of the application of iTBS over the Left DLPFC , followed by 1 Hz inhibition over the Right DLPFC. To measure the level of Depression and Anxiety every patient filled a Patient Health Questionary (PHQ-9) and a Hamilton Anxiety Rating Scale (HARS) before and after the treatment. The statistical analysis was made using SPSS. Results: Treatment response was found in 16 patients (50%), while remission was confirmed in 9 patients (28%). Remission from depression was higher than from the symptoms of anxiety(28% vs 21.87%). The response rate for anxiety was 43.75%. The reduction of anxiety symptoms was found in both, the somatic (53% of patients responded) and the psychological symptoms (34% of patients responded).The decreases in scores in both PQH-9 and HARS were statistically significant. Conclusion: The bilateral protocol applied has shown adequate results in the improvement and remission in symptoms of both, depression and anxiety.

Bioelectromagnetics, 2019

It is well known that applying transcranial alternating current stimulation (tACS) to the scalp c... more It is well known that applying transcranial alternating current stimulation (tACS) to the scalp can generate artefactual visual perceptions of flashing or shimmering light known as phosphenes. The thresholds for generating these phosphenes have been used by international standards bodies to provide conservative estimates of the field strength required to interfere with human neural functioning and set safety limits accordingly. However, the precise relationship between electric currents and phosphene perception thresholds remains uncertain. The present study used tACS to systematically investigate the effects of the location and the frequency of stimulation on phosphene perception thresholds. These thresholds were obtained from 24 participants using a within‐subject design as a function of scalp stimulation sites (FPz‐Cz versus Oz‐Cz) and stimulation frequency (2–30 Hz in steps of 2 Hz). Phosphene perception thresholds were consistently lower for FPz‐Cz stimulation, and regardless o...

bioRxiv (Cold Spring Harbor Laboratory), Oct 10, 2018

up to 750 characters): 750 characters Although magnetophosphene perception is the most reliable r... more up to 750 characters): 750 characters Although magnetophosphene perception is the most reliable reported effect on acute human neurophysiological responses to extremely low frequency (ELF) magnetic field (MF) exposure, current knowledge is based on small sample size, non-replicated experiments. In this study, we established MF levels triggering magnetophosphenes at 20, 50, 60 and 100 Hz in humans. Magnetophosphene perception and EEG were collected in 55 magnetic flux density conditions randomly delivered in each frequency group (2 experiments, total n=145). Results indicate that threshold values 1) need to be reported as a function of dB/dt instead of flux density, and 2) are frequency-dependent (higher sensitivity to lower frequencies). No clear trend was found in EEG data.

fMRI full experiment 3000 microTesla part

HAL (Le Centre pour la Communication Scientifique Directe), May 3, 2018

Bioelectromagnetics, Oct 1, 2022

Numerous studies have been carried out on the potential effects of an extremely low frequency (EL... more Numerous studies have been carried out on the potential effects of an extremely low frequency (ELF-0-300 Hz) magnetic field (MF) on human health. However, there is limited data on the effect of a high exposure level to ELF MFs for a prolonged period. Therefore, the objective of this pilot work was to demonstrate the feasibility of a study evaluating the stress hormone concentrations resulting from a 10-min exposure to a 60 Hz MF of several tens of thousands of µT. In this pilot study, human volunteers were thus exposed for the first time to a 60 Hz, 50 mT MF for a duration of 10 min. Stress hormone levels were measured before (once), during (twice) and after (once) this 10-min exposure period. The small sample size (n = 5) did not allow to conduct standard inferential statistical tests and no conclusion regarding the exposure effects can be drawn. However, this study demonstrates the feasibility of using a simple blood testing material in a protocol testing for the effect of a 10-min exposure to a high MF level in healthy human volunteers.

Brain Stimulation, Mar 1, 2017

Bioelectromagnetics

Electric fields from both extremely low‐frequency magnetic fields (ELF‐MF) and alternating curren... more Electric fields from both extremely low‐frequency magnetic fields (ELF‐MF) and alternating current (AC) stimulations impact human neurophysiology. As the retinal photoreceptors, vestibular hair cells are graded potential cells and are sensitive to electric fields. Electrophosphene and magnetophosphene literature suggests different impacts of AC and ELF‐MF on the vestibular hair cells. Furthermore, while AC modulates the vestibular system more globally, lateral ELF‐MF stimulations could be more utricular specific. Therefore, to further address the impact of ELF‐MF‐induced electric fields on the human vestibular system and the potential differences with AC stimulations, we investigated the effects of both stimulation modalities on the perception of verticality using a subjective visual vertical (SVV) paradigm. For similar levels of SVV precision, the ELF‐MF condition required more time to adjust SVV, and SVV variability was higher with ELF‐MF than with AC vestibular‐specific stimulati...

IEEE Access, 2020

Background: International agencies recognize the lack of knowledge to further establish standards... more Background: International agencies recognize the lack of knowledge to further establish standards and guidelines to protect the workers and the public from extremely low-frequency magnetic fields (ELF-MF). In that regard, postural control has been proposed as a biomarker of potential adverse effects in humans. Considering its crucial role in postural control and its specific neurophysiological characteristics, the vestibular system emerges as an ELF-MF likely target. However, postural modulation to vestibular ELF-MF exposure remains inconclusive. Previous studies led us to investigate stimulation orientation and point of application to clarify the ELF-MF impact on balance in humans. Objectives: This research aimed to investigate the acute postural impact of lateral vestibular-specific ELF-MF stimulations. Methods: Postural control of thirty eight healthy participants was analyzed with lateral vestibular-specific ELF-MF stimulations ranging from 20 Hz to 160 Hz, up to 142 T/s and vestibular electrical stimulations at the same frequencies. Both spatial orientation and quantity of movement variables were used to investigate postural modulations. Results: Despite a conclusive positive control effect, no significant effects of ELF-MF and alternating current stimulation exposures were found regardless of frequency conditions. Conclusions: Although important electric fields were generated, no postural modulation was found. However, at these frequencies, the potential vestibular activation did not translate into functional postural sway but might be observed with reflexive vestibular outcomes. INDEX TERMS Electromagnetic induction, extremely low frequency magnetic fields, human vestibular system, postural control.

Neurophysiologie Clinique/Clinical Neurophysiology, 2015

s du XXII e congrès de la Société francophone posture équilibre locomotion (SOFPEL) 413 petite, p... more s du XXII e congrès de la Société francophone posture équilibre locomotion (SOFPEL) 413 petite, plus petite, égale, plus grande ou beaucoup plus grande (échelle de −2 à +2) sur le pied que sur le front. Résultats Les nombres de patients discriminant les deux stimuli étaient, pour les distances de 8 et 20 mm respectivement : 3 et 8 sur P, 10 et 10 sur NP. Comparativement au front, les distances de 8 et 20 mm étaient perçues plus grandes par 10 et 3 patients sur P, et par 1 et 0 sur NP (égalité dans tous les autres cas). Discussion-conclusion Au-delà des modifications des seuils des récepteurs, l'EIAPIt4 semble influencer la représentation somesthésique des distances corporelles. L'hypothèse qu'une telle perturbation durable laisse une trace au niveau des cartes somatotopiques centrales reste à tester. Mots clés Épine irritative d'appui plantaire inconsciente ; Somesthésie plantaire ; Représentation du corps Déclaration de liens d'intérêts Les auteurs déclarent ne pas avoir de liens d'intérêts.

Time-varying Magnetic Fields (MF) are a cornerstone of major modern healthcare technologies and a... more Time-varying Magnetic Fields (MF) are a cornerstone of major modern healthcare technologies and are also a byproduct of our modern environment. Virtually everyone is exposed to power-frequency MF (50/60 Hz), inducing in our body electric fields and currents, potentially modulating brain function. MF-induced electric fields within the central nervous system can generate flickering visual perceptions (magnetophosphenes), which form the basis of international MF exposure guidelines and recommendations protecting workers and the general public. However, magnetophosphene perception thresholds were estimated 40 years ago in a small, unreplicated study with significant uncertainties and leaving open the question of the underlying mechanism. Here, we report magnetophosphene perception in 81 volunteers exposed to MF (eye or occipital exposure) between 0 and 50 mT at frequencies of 20, 50, 60 and 100 Hz. Frequency-dependent threshold were quantified and support an interaction between induced ...

IEEE Access

This work involved human subjects or animals in its research. Approval of all ethical and experim... more This work involved human subjects or animals in its research. Approval of all ethical and experimental procedures and protocols was granted by the Institutional Review Board of Euromov-DHM Laboratory at the University of Montpellier, France, under Application IRB 2001D, and performed in line with the Declaration of Helsinki.

2019 IEEE Radio and Antenna Days of the Indian Ocean (RADIO), 2019

Current guidelines and recommendations limiting human exposure to extremely low frequency (ELF) m... more Current guidelines and recommendations limiting human exposure to extremely low frequency (ELF) magnetic field (MF) are based on the most reliable acute human neurophysiological exposure responses. However, the currently available perception thresholds are established on small sample size and non-replicated experiments. The current human study aimed to test MF levels leading to mahnetophosphenes perceptions at 20, 50, 60 and 100 Hz. Perception reported button-press were recorded in these 4 frequency groups in 55 randomly assigned magnetic flux density conditions. Results showed a frequency-dependent threshold for initial perception: 2.51 T/s at 20 Hz, 6.28 T/s at 50 Hz, 7.54 T/s at 60 Hz, and 12.57 T/s at 100 Hz; and for the 50% detection rate: 4.73 T/s at 20 Hz, 8.83 T/s at 50 Hz, 10.55 T/s at 60 Hz, and 33.46 T/s at 100 Hz. Since it is a linear correlate of the induced in-situ E-fields, the dB/dt metric was chosen to analyse the the data. It confirmed lower magnetophoshene perception at lower frequencies for a similar in-situ induced E-field.