Influence of magnetic fields and their characteristics on cortical excitabilitystudy on healthy adults and pathological aging

Abstract

This doctoral thesis intended to answer two questions in relation to the interaction between dynamic and static magnetic fields, and the motor cortex. During the first two experiments, we studied factors that influence the reproducibility of transcranial magnetic stimulation (TMS). These investigations have shown that two types of relevant factors impact the effects and the reproducibility of the TMS: (1) technical or modifiable factors, in particular the TMS pulse waveform and current direction; and (2) physiological factors, specifically the influence of physiological aging and age-related diseases, such as Dementia due to Alzheimer's disease and type 2 Diabetes Mellitus. In a second type of study, a reduction of motor cortex excitability and reactivity was observed after applying transcranial static magnetic stimulation (tSMS). However, this reduction was only captured by a specific type of TMS waveform, indicating that the action of the tSMS is centered on specific cortical interneuron networks. Electroencephalographic recordings quantified an increase in the range of beta frequencies in fronto-central regions, this increase was negatively correlated with the reduction in cortical excitability.