title: Physiologically evoked neuronal current MRI in a bloodless turtle brain: detectable or not?
abstract: Contradictory reports regarding the detection of neuronal currents have left the feasibility of neuronal current MRI (ncMRI) an open question. Most previous ncMRI studies in human subjects are suspect due to their inability to separate or eliminate hemodynamic effects. In this study, we used a bloodless turtle brain preparation that eliminates hemodynamic effects, to explore the feasibility of detecting visually-evoked ncMRI signals at 9.4 T. Intact turtle brains, with eyes attached, were dissected from the cranium and placed in artificial cerebral spinal fluid. Light flashes were delivered to the eyes to evoke neuronal activity. Local field potential (LFP) and MRI signals were measured in an interleaved fashion. Robust visually-evoked LFP signals were observed in turtle brains, but no significant signal changes synchronized with neuronal currents were found in the ncMRI images. In this study, detection thresholds of 0.1% and 0.1 degrees were set for MRI magnitude and phase signal changes, respectively. The absence of significant signal changes in the MRI images suggests that visually-evoked ncMRI signals in the turtle brain are below these detectable levels.
authors.affiliation: Brain Research Imaging Center and Department of Radiology, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Qingfei
authors.initials: Q
authors.lastname: Luo
authors.forename: Huo
authors.initials: H
authors.lastname: Lu
authors.forename: Hanbing
authors.initials: H
authors.lastname: Lu
authors.forename: David
authors.initials: D
authors.lastname: Senseman
authors.forename: Keith
authors.initials: K
authors.lastname: Worsley
authors.forename: Yihong
authors.initials: Y
authors.lastname: Yang
authors.forename: Jia-Hong
authors.initials: JH
authors.lastname: Gao
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D002560:Cerebrovascular Circulation; D005074:Evoked Potentials, Visual / Q000502:physiology*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009474:Neurons / Q000502:physiology*; D014426:Turtles / Q000502:physiology*