Dr Zsolt Turi | Prospective electric field estimation method for dosing repetitive transcranial magnetic stimulation in humans

Guest Lecture

  • Date: Mar 22, 2019
  • Time: 01:00 PM - 02:00 PM (Local Time Germany)
  • Speaker: Dr Zsolt Turi
  • Department of Clinical Neurophysiology, University Medical Center Goettingen, Germany
  • Location: MPI for Human Cognitive and Brain Sciences
  • Room: Wilhelm Wundt Room (A400)
Neurons do not only generate extracellular electric fields (E-fields), they are also responsive to them, irrespective of whether the electric field is generated endogenously or applied exogenously. Whereas observational methods are essential for characterizing the spatial and temporal dynamics of neural oscillations, interventional methods allow one to manipulate neural oscillations or even ameliorate altered neural activity in neuropsychiatric disorders. Non-invasive brain stimulation (NIBS) techniques, such as repetitive transcranial magnetic stimulation (rTMS) are interventional methods that aim to achieve these goals in humans. However, a deeper understanding of the neural mechanisms underlying the rTMS-induced effects is necessary both for neuroscience research and clinical applications.

Because the electrophysiological and functional effects of electrical brain stimulation methods are strongly dependent on the magnitude of the exogenous E-field, identifying the boundary conditions for effective magnitudes is an essential step. Converging evidence from neocortical brain slice preparations and in vivo rodent experiments indicate that 15-60 cycles of 1-5 mV/mm strong E-fields already induce week but stable immediate electrophysiological effects in the neocortex. By convention, rTMS studies define the stimulation intensity rather than the magnitude of the E-field. Retrospective estimations and validation measurements of conventional doses reveal that rTMS use E-fields above 60 mV/mm in humans. Therefore, we hypothesized to observe neural entrainment effects by using much lower E-field magnitudes for rTMS when compared to conventional dosing.

To test our hypothesis, we combined most advanced practices to implement our approach where prospective computational modeling guided the choice of stimulation intensity at the single subject level, individual peak frequency estimation fine-tuned the choice of stimulation frequency and real time neuronavigation ensured accurate targeting.
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