Doctor of Philosophy
The vestibular system is extremely sensitive to electric fields (E-fields). Indeed, vestibular hair cells are graded potential cells and this property makes them very susceptible to small membrane potential modulations. Studies show that extremely low-frequency magnetic fields (ELF-MF) induced E-fields impact postural control in which the vestibular system plays an important role. However, the knowledge of whether this is indeed a vestibular specific effect is still pending.
Considering its crucial role and the specific neurophysiological characteristics of its hair cells, the vestibular system emerges as an ELF-MF likely target
The three studies presented in this thesis aimed to further address whether ELF-MF modulate vestibular-driven outcomes.
Studies 1 and 2 aimed to investigate postural responses while more specifically targeting the vestibular system. However, we did not find any modulation in either study. Nonetheless, based on both studies, study 3 aimed to determine whether the orientation and frequency of our stimulations were more likely to target the otoliths. Therefore, the third study looked at the subjective visual vertical. Here, we found a potential ELF-MF utricular modulation.
This thesis is the first steppingstone in a new field of research. Further investigations regarding the interaction between the ELF-MF and the vestibular system will have to look at more reflexives vestibular outcomes. Nonetheless, this thesis provides valuable information that will need to be taken into consideration when writing future international guidelines and standards related to ELF-MF.
Summary for Lay Audience
Without noticing it, because of electricity generation and use, electromagnetic fields surround us in our daily lives. When sufficiently strong, these fields generate electrical currents inside the body. Such currents can modulate the physiologic electric information transiting in the form of electrical signals propagating inside the nerves. This impact raises health and safety concerns regarding the interactions between these fields and human neurophysiology. The most constant and sensitive response to electromagnetic fields resulting from power generation and transport is the perception of flickering lights appearing in the peripheral visual field. It underlines an interaction with cells in the retina. This phenomenon is used as the model for the interaction between the so-called extremely low frequency electromagnetic fields (ELF-MF) and the brain and is adopted as the basis for international guidelines and standards, setting the exposure limits to avoid adverse human effects. However, there are still several gaps in our overall knowledge of the threshold effects and our understanding of the precise interaction mechanisms and looking at the impact on other sensory systems could provide potential answers.
The vestibular system is a little sensory organ nestled within the inner ear. It is known as the balance system. This tiny sensory system has sensors extremely sensitive to electrical stimulations, which are also very close neurophysiologically to the sensors found within the retina. Therefore, the vestibular system seems to be a good alternate model to study the impact of low frequency electromagnetic fields on human neurophysiology.
This thesis explores the impact of electric and magnetic signals applied to the vestibular system by looking at balance in the first two studies and space perception in the third study. We did not find balance differences in outcomes when we stimulated the participants. However, the study on space perception showed that the ELF-MF could have modulated a subsystem within the vestibular system.
Altogether this thesis stresses useful information for the safety of both the public and the workers subjected to ELF-MF. Finally, this thesis is the first steppingstone in this relatively new research avenue and further research related to the vestibular system will need to be investigated in the future.
Bouisset, Nicolas, "Impact of Extremely Low-Frequency Magnetic and Electric Stimuli on Vestibular-Driven Outcomes" (2020). Electronic Thesis and Dissertation Repository. 7562.