Tms-evoked potentials in physiological ageing and Alzheimer’s disease

The cortical response to a transcranial magnetic stimulation (TMS) pulse seen in electroencephalography (EEG), the TMS-evoked potential (TEP), relies on the integrity of the stimulated cortex and also on its white matter (WM) connections to neighboring and distant areas. Consequently, TEPs should be affected in pathological conditions associated with progressive WM damage, such as Alzheimer’s disease (AD), either in the intensity of the signal or in their shape. Demonstrating that TEPs can track neurodegeneration would make TEPs both a novel biomarker for AD and possibly other neurodegenerative disorders. Previous studies had linked the propagation of TEPs in the cortex to structural networks, highlighting the relation between TEPs and WM tracts in healthy subjects. In the present study, we are collecting TEPs in healthy elderly individuals and patients with Alzheimer’s disease at various stages of the disease. TEPs are elicited from stimulation at parietal nodes of the default mode network as well as stimulation of frontal nodes of the executive control network, as both networks are known to be affected by AD. We predict that the TEPs from the AD group will be significantly less intense in the early part of the epoch, i.e., the first 100 milliseconds, the part of the epoch less affected by TMS-induced sensory artifacts, than the healthy controls. In addition, we expect the early TEP components to be significantly slower in the AD group than in the control group.