TMS-induced BOLD changes to assess inter- and intraindividual differences in brain excitability: An interleaved TMS-fMRI approach

COEX 

New advancements in interleaved TMS-fMRI provides us with invaluable insights into excitability states of the brain due to TMS. In this talk a series of studies addressing variability in brain excitability due to internal states and subject-specific traits will be discussed. First, we will discuss differences in excitability between the primary motor cortex and the DLPFC on a local as well as a network level. Then sex-differences in DLPFC excitability for local and downstream brain areas will be highlighted. Further, we will show how brain state influences interactions between DLPFC and downstream areas by systematically manipulating brain states via a working memory task. Finally, we will show how task responses relate to the actual E-fields induced by stimulation to spot interactions between excitability-modulated areas and behavioural outcomes.
In sum the integration of fMRI with TMS presents a significant methodological benefit in examining the variability of TMS responses, i.e. specific excitability states. Especially, it allows us to understand brain excitability variability in different cortical areas as well as network effects of brain excitability states. With this knowledge stimulation intensities might be improved to apply person specific stimulation doses. Moreover, better timing might result in better interactions between excitability states and stimulation.
These insights have the potential to improve TMS treatment in neuropsychiatric populations moving a step forward to personalized interventions.