title: Column-based model of electric field excitation of cerebral cortex.
abstract: A model to explain the orientation selectivity of the neurophysiologic effects of electric-field transients applied to cerebral cortex is proposed and supported with neuroimaging evidence. Although it is well known that transcranial magnetic stimulation (TMS) excites cerebral cortex in an orientation-selective manner, a neurophysiologically compelling explanation of this phenomenon has been lacking. It is generally presumed that TMS-induced excitation is mediated by horizontal fibers in the cortical surfaces nearest to the stimulating coil, i.e., at the gyral crowns. No evidence exists, however, that horizontal fibers are orientation selective either anatomically or physiologically. We used positron emission tomography to demonstrate that TMS-induced cortical activation is selectively sulcal. This observation allows the well-established columnar organization of cerebral cortex to be invoked to explain the observed orientation selectivity. In addition, Rushton's cosine principle can used to model stimulation efficacy for an electrical field applied at any cortical site at any intensity and in any orientation.
authors.affiliation: Research Imaging Center, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA. fox@uthscsa.edu
authors.forename: Peter T
authors.initials: PT
authors.lastname: Fox
authors.forename: Shalini
authors.initials: S
authors.lastname: Narayana
authors.forename: Nitin
authors.initials: N
authors.lastname: Tandon
authors.forename: Hugo
authors.initials: H
authors.lastname: Sandoval
authors.forename: Sarabeth P
authors.initials: SP
authors.lastname: Fox
authors.forename: Peter
authors.initials: P
authors.lastname: Kochunov
authors.forename: Jack L
authors.initials: JL
authors.lastname: Lancaster
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000033:anatomy & histology* / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009068:Movement / Q000502:physiology*; D014055:Tomography, Emission-Computed