Exploring electrophysiological properties of the angular gyrus using the combination of TMS and EEG

Details

Supervisors

Hanseeuw, Bernard ; Mouraux, André

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

Alzheimer's disease (AD) is the most common neurodegenerative disease and the most prevalent cause of dementia. According to previous studies, GABAergic inhibition may be impaired in subjects who develop AD later in life, leading to a change in the excitation-inhibition balance. One of the first neocortical regions affected by amyloidosis in early AD is the angular gyrus (AG), a part of the parietal cortex. Therefore, it would be interesting to probe the electrophysiological properties of AG in the early stages of AD to uncover any changes in the excitation-inhibition balance. Although the recent development of combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) allows such an exploration, only a few research groups have explored the properties of non-motor cortical areas, and no studies characterized the AG. The aim of this project was to determine the optimal stimulation parameters for recording TMS evoked brain potentials (TEPs) from this area. To this end, we conducted the first study on 19 young and healthy subjects in which we tested two TMS coil positions over the AG (across or along the superior temporal sulcus, STS), two current directions (normal or reversed), and 3 intensities of stimulation (100%, 120% and 140 %rMT). We recorded the brain response to TMS stimuli with a 32- electrode TMS-compatible EEG system. As a result of this first part, we identified that the best combination of parameters for recording TEPs from the AG was a combination of a coil placed along the STS with a reversed current flowing through it to minimize the induced muscular contraction that contaminates TEPs. Short-latency intracortical inhibition (SICI) can be observed in motor-evoked potentials following paired-pulse TMS stimulation of the primary motor cortex and is considered as a correlate of local GABAA receptors-mediated neurotransmission. We used the results of the first study to adapt a paired-pulse protocol, and we are currently running a follow-up study to evaluate SICI in the AG. In this second part, we test different conditioning stimulus intensities (60, 80, 100% of resting motor threshold) to identify the best way to measure SICI in the AG and, thereby, test GABAA receptor-mediated neurotransmission in this cortical area in young and healthy subjects before applying it to the elderly population and Alzheimer's patients.