title: Direct neural current imaging in an intact cerebellum with magnetic resonance imaging.
abstract: The ability to detect neuronal currents with high spatiotemporal resolution using magnetic resonance imaging (MRI) is important for studying human brain function in both health and disease. While significant progress has been made, we still lack evidence showing that it is possible to measure an MR signal time-locked to neuronal currents with a temporal waveform matching concurrently recorded local field potentials (LFPs). Also lacking is evidence that such MR data can be used to image current distribution in active tissue. Since these two results are lacking even in vitro, we obtained these data in an intact isolated whole cerebellum of turtle during slow neuronal activity mediated by metabotropic glutamate receptors using a gradient-echo EPI sequence (TR=100ms) at 4.7T. Our results show that it is possible (1) to reliably detect an MR phase shift time course matching that of the concurrently measured LFP evoked by stimulation of a cerebellar peduncle, (2) to detect the signal in single voxels of 0.1mm(3), (3) to determine the spatial phase map matching the magnetic field distribution predicted by the LFP map, (4) to estimate the distribution of neuronal current in the active tissue from a group-average phase map, and (5) to provide a quantitatively accurate theoretical account of the measured phase shifts. The peak values of the detected MR phase shifts were 0.27-0.37°, corresponding to local magnetic field changes of 0.67-0.93nT (for TE=26ms). Our work provides an empirical basis for future extensions to in vivo imaging of neuronal currents.
authors.affiliation: Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: padma@nmr.mgh.harvard.edu.
authors.forename: Padmavathi
authors.initials: P
authors.lastname: Sundaram
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA. Electronic address: nummenma@nmr.mgh.harvard.edu.
authors.forename: Aapo
authors.initials: A
authors.lastname: Nummenmaa
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: sw@bwh.harvard.edu.
authors.forename: William
authors.initials: W
authors.lastname: Wells
authors.affiliation: Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: darren.orbach@childrens.harvard.edu.
authors.forename: Darren
authors.initials: D
authors.lastname: Orbach
authors.affiliation: Department of Neurosurgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: dorringe@med.umich.edu.
authors.forename: Daniel
authors.initials: D
authors.lastname: Orringer
authors.affiliation: Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: robert.mulkern@childrens.harvard.edu.
authors.forename: Robert
authors.initials: R
authors.lastname: Mulkern
authors.affiliation: Department of Newborn Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA 02215, USA. Electronic address: yoshio.okada@childrens.harvard.edu.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Okada
mesh_terms: D000818:Animals; D001931:Brain Mapping / Q000379:methods*; D058256:Brain Waves; D002531:Cerebellum / Q000502:physiology*; D004558:Electric Stimulation; D055724:Electrophysiological Phenomena; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D012815:Signal Processing, Computer-Assisted; D014426:Turtles