title: Propagating Neural Source Revealed by Doppler Shift of Population Spiking Frequency.
abstract: Electrical activity in the brain during normal and abnormal function is associated with propagating waves of various speeds and directions. It is unclear how both fast and slow traveling waves with sometime opposite directions can coexist in the same neural tissue. By recording population spikes simultaneously throughout the unfolded rodent hippocampus with a penetrating microelectrode array, we have shown that fast and slow waves are causally related, so a slowly moving neural source generates fast-propagating waves at ∼0.12 m/s. The source of the fast population spikes is limited in space and moving at ∼0.016 m/s based on both direct and Doppler measurements among 36 different spiking trains among eight different hippocampi. The fact that the source is itself moving can account for the surprising direction reversal of the wave. Therefore, these results indicate that a small neural focus can move and that this phenomenon could explain the apparent wave reflection at tissue edges or multiple foci observed at different locations in neural tissue.
  
  
  CONCLUSIONS
  The use of novel techniques with an unfolded hippocampus and penetrating microelectrode array to record and analyze neural activity has revealed the existence of a source of neural signals that propagates throughout the hippocampus. The source itself is electrically silent, but its location can be inferred by building isochrone maps of population spikes that the source generates. The movement of the source can also be tracked by observing the Doppler frequency shift of these spikes. These results have general implications for how neural signals are generated and propagated in the hippocampus; moreover, they have important implications for the understanding of seizure generation and foci localization.
authors.affiliation: Neural Engineering Center, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106.
authors.forename: Mingming
authors.identifier: http://orcid.org/0000-0002-5384-6363
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Neural Engineering Center, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106.
authors.forename: Rajat S
authors.initials: RS
authors.lastname: Shivacharan
authors.affiliation: Neural Engineering Center, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106.
authors.forename: Chia-Chu
authors.initials: CC
authors.lastname: Chiang
authors.affiliation: Neural Engineering Center, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106.
authors.forename: Luis E
authors.initials: LE
authors.lastname: Gonzalez-Reyes
authors.affiliation: Neural Engineering Center, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106 dxd6@case.edu.
authors.forename: Dominique M
authors.initials: DM
authors.lastname: Durand
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000465:Algorithms; D000818:Animals; D001931:Brain Mapping / Q000295:instrumentation* / Q000379:methods; D058256:Brain Waves / Q000502:physiology*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006624:Hippocampus / Q000502:physiology*; D008297:Male; D051379:Mice; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D046888:Tissue Array Analysis / Q000295:instrumentation / Q000379:methods
keywords: hippocampus; moving source; neural signal propagation