Le système nerveux central est la cible la plus probable d'effets biologiques dûs à l'exposition aux radiofréquences (RF) de la téléphonie mobile. Plusieurs études sur l’EEG (électroencéphalogramme) ont montré des variations dans le spectre de la bande alpha pendant et / ou après l'exposition aux radiofréquences, avec les yeux fermés ou pendant le sommeil. Dans ce contexte, l'observation de l'activité électrique spontanée des réseaux neuronaux sous exposition aux radiofréquences représente un outil efficace pour détecter de possibles effets des RF de faible niveau sur le système nerveux. Dans ce travail de thèse, nous avons développé un dispositif expérimental dédié à l'exposition dans la gamme des GHz de réseaux neuronaux et permettant simultanément l’enregistrement de l'activité électrique des neurones. Une cellule électromagnétique transversale (TEM) a été utilisée afin d'exposer les réseaux neuronaux aux signaux GSM-1800 à un niveau de DAS de 3,2 W / kg. L'enregistrement de l'activité électrique neuronale et la détection en termes de spikes et bursts sous exposition ont été réalisées à l'aide de réseaux de micro-électrodes (MEAs). Ce travail démontre la faisabilité de l’étude (culture de réseaux de neurones primaires, enregistrement de l'activité électrique et analyse des signaux obtenus sous exposition aux radiofréquences) et expose des résultats préliminaires. Dans l'expérience principale (16 cultures), il y avait une diminution réversible de 30% du taux moyen de spikes (MFR) et de bursts (BR) pendant les 3 min d’exposition aux RF. Des expériences supplémentaires sont nécessaires pour mieux caractériser cet effet, notamment en termes d'élévation de la température au niveau microscopique. / The central nervous system is the most likely target of mobile telephony radiofrequency field (RF) exposure in terms of biological effects. Several EEG (electroencephalography) studies have reported variations in the alpha-band power spectrum during and/or after RF exposure, in resting EEG and during sleep. In this context, the observation of the spontaneous electrical activity of neuronal networks under RF exposure can be an efficient tool to detect the occurrence of low-level RF effects on the nervous system. In this thesis research work we developed a dedicated experimental setup in the GHz range for the simultaneous exposure of neuronal networks and monitoring of electrical activity. A transverse electromagnetic (TEM) cell was used to expose the neuronal networks to GSM-1800 signals at a SAR level of 3.2 W/kg. Recording of the neuronal electrical activity and detection of the extracellular spikes and bursts under exposure were performed using Micro Electrode Arrays (MEAs). This work provides the proof of feasibility and preliminary results of the integrated investigation regarding exposure setup, culture of the neuronal network, recording of the electrical activity and analysis of the signals obtained under RF exposure. In the main experiment (16 cultures), there was a 30% reversible decrease in mean firing rate (MFR) and bursting rate (BR) during the 3 min exposures to RF. Additional experiments are needed to further characterize this effect, especially in terms of temperature elevation at the microscopic level.

For almost a century, the electrical properties of the brain and the nervous system have been investigated to gain a better understanding of their mechanisms and to find cures for pathological conditions. Despite the fact that today's advancements in surgical techniques, research, and medical imaging have improved our ability to treat brain disorders, our knowledge of the brain and its functions is still limited. Culturing dissociated cortical neurons on Micro-Electrode Array dishes is a powerful experimental tool for investigating functional and structural characteristics of in-vitro neuronal networks, such as the cellular basis of brain learning, memory and synaptic developmental plasticity. This dissertation focuses on combining MEAs with novel electrophysiology experimental paradigms and statistical data analysis to investigate the mechanisms that regulate brain development at the level of synaptic formation and growth cones. The goal is to use a mathematical approach and specifically designed experiments to investigate whether dissociated neuronal networks can dependably display long and short-term plasticity, which are thought to be the building blocks of memory formation in the brain. Quantifying the functional evolution of dissociated neuronal networks during in- vitro development, using a statistical analysis tool was the first aim of this work. The results of the False Discovery Rate analysis show an evolution in network activity with changes in both the number of statistically significant stimulus/recording pairs as well as the average length of connections and the number of connections per active node. It is therefore proposed that the FDR analysis combined with two metrics, the average connection length and the number of highly connected "supernodes" is a valuable technique for describing neuronal connectivity in MEA dishes. Furthermore, the statistical analysis indicates that cultures dissociated from the same brain tissue display trends in their temporal evolution that are more similar than those obtained with respect to different batches. The second aim of this dissertation was to investigate long and short-term plasticity responsible for memory formation in dissociated neuronal networks. In order to address this issue, a set of experiments was designed and implemented in which the MEA electrode grid was divided into four quadrants, two of which were chronically stimulated, every two days for one hour with a stimulation paradigm that varied over time. Overall network and quadrant responses were then analyzed to quantify what level of plasticity took place in the network and how this was due to the stimulation interruption. The results demonstrate that here were no spatial differences in the stimulus-evoked activity within quadrants. Furthermore, the implemented stimulation protocol induced depression effects in the neuronal networks as demonstrated by the consistently lower network activity following stimulation sessions. Finally, the analysis demonstrated that the inhibitory effects of the stimulation decreased over time, thus suggesting a habituation phenomenon. These findings are sufficient to conclude that electrical stimulation is an important tool to interact with dissociated neuronal cultures, but localized stimuli are not enough to drive spatial synaptic potentiation or depression. On the contrary, the ability to modulate synaptic temporal plasticity was a feasible task to achieve by chronic network stimulation. / Electrical and Computer Engineering

The central nervous system is the most likely target of mobile telephony radiofrequency field (RF) exposure in terms of biological effects. Several EEG (electroencephalography) studies have reported variations in the alpha-band power spectrum during and/or after RF exposure, in resting EEG and during sleep. In this context, the observation of the spontaneous electrical activity of neuronal networks under RF exposure can be an efficient tool to detect the occurrence of low-level RF effects on the nervous system. In this thesis research work we developed a dedicated experimental setup in the GHz range for the simultaneous exposure of neuronal networks and monitoring of electrical activity. A transverse electromagnetic (TEM) cell was used to expose the neuronal networks to GSM-1800 signals at a SAR level of 3.2 W/kg. Recording of the neuronal electrical activity and detection of the extracellular spikes and bursts under exposure were performed using Micro Electrode Arrays (MEAs). This work provides the proof of feasibility and preliminary results of the integrated investigation regarding exposure setup, culture of the neuronal network, recording of the electrical activity and analysis of the signals obtained under RF exposure. In the main experiment (16 cultures), there was a 30% reversible decrease in mean firing rate (MFR) and bursting rate (BR) during the 3 min exposures to RF. Additional experiments are needed to further characterize this effect, especially in terms of temperature elevation at the microscopic level.