title: Solving the orientation specific constraints in transcranial magnetic stimulation by rotating fields.
abstract: Transcranial Magnetic Stimulation (TMS) is a promising technology for both neurology and psychiatry. Positive treatment outcome has been reported, for instance in double blind, multi-center studies on depression. Nonetheless, the application of TMS towards studying and treating brain disorders is still limited by inter-subject variability and lack of model systems accessible to TMS. The latter are required to obtain a deeper understanding of the biophysical foundations of TMS so that the stimulus protocol can be optimized for maximal brain response, while inter-subject variability hinders precise and reliable delivery of stimuli across subjects. Recent studies showed that both of these limitations are in part due to the angular sensitivity of TMS. Thus, a technique that would eradicate the need for precise angular orientation of the coil would improve both the inter-subject reliability of TMS and its effectiveness in model systems. We show here how rotation of the stimulating field relieves the angular sensitivity of TMS and provides improvements in both issues. Field rotation is attained by superposing the fields of two coils positioned orthogonal to each other and operated with a relative phase shift in time. Rotating field TMS (rfTMS) efficiently stimulates both cultured hippocampal networks and rat motor cortex, two neuronal systems that are notoriously difficult to excite magnetically. This opens the possibility of pharmacological and invasive TMS experiments in these model systems. Application of rfTMS to human subjects overcomes the orientation dependence of standard TMS. Thus, rfTMS yields optimal targeting of brain regions where correct orientation cannot be determined (e.g., via motor feedback) and will enable stimulation in brain regions where a preferred axonal orientation does not exist.
authors: Department of Physics and SEAS, Harvard University, Cambridge, Massachusetts, United States of America.
authors: Assaf
authors: A
authors: Rotem
authors: Bernstein Center for Computational Neuroscience, Goettingen, Germany.
authors: Andreas
authors: A
authors: Neef
authors: Department of Clinical Neurophysiology, University Medicine Goettingen, Goettingen, Germany ; Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors: Nicole E
authors: NE
authors: Neef
authors: Max Planck Institute for Dynamics and Self-Organization, Goettingen, Germany.
authors: Andres
authors: A
authors: Agudelo-Toro
authors: Chemical Physics Department, Weizmann Institute of Science, Rehovot, Israel.
authors: David
authors: D
authors: Rakhmilevitch
authors: Department of Clinical Neurophysiology, University Medicine Goettingen, Goettingen, Germany.
authors: Walter
authors: W
authors: Paulus
authors: Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot, Israel.
authors: Elisha
authors: E
authors: Moses
mesh_terms: D000818:Animals; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D060526:Magnetic Fields; D008297:Male; D008954:Models, Biological; D051381:Rats; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation / Q000379:methods