title: Neural and hemodynamic responses elicited by forelimb- and photo-stimulation in channelrhodopsin-2 mice: insights into the hemodynamic point spread function.
abstract: Hemodynamic responses are commonly used to map brain activity; however, their spatial limits have remained unclear because of the lack of a well-defined and malleable spatial stimulus. To examine the properties of neural activity and hemodynamic responses, multiunit activity, local field potential, cerebral blood volume (CBV)-sensitive optical imaging, and laser Doppler flowmetry were measured from the somatosensory cortex of transgenic mice expressing Channelrhodopsin-2 in cortex Layer 5 pyramidal neurons. The magnitude and extent of neural and hemodynamic responses were modulated using different photo-stimulation parameters and compared with those induced by somatosensory stimulation. Photo-stimulation-evoked spiking activity across cortical layers was similar to forelimb stimulation, although their activity originated in different layers. Hemodynamic responses induced by forelimb- and photo-stimulation were similar in magnitude and shape, although the former were slightly larger in amplitude and wider in extent. Altogether, the neurovascular relationship differed between these 2 stimulation pathways, but photo-stimulation-evoked changes in neural and hemodynamic activities were linearly correlated. Hemodynamic point spread functions were estimated from the photo-stimulation data and its full-width at half-maximum ranged between 103 and 175 µm. Therefore, submillimeter functional structures separated by a few hundred micrometers may be resolved using hemodynamic methods, such as optical imaging and functional magnetic resonance imaging.
authors.affiliation: Neuroimaging Laboratory, Department of Radiology, Department of Bioengineering.
authors.forename: Alberto L
authors.initials: AL
authors.lastname: Vazquez
authors.affiliation: Neuroimaging Laboratory, Department of Radiology.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, USA.
authors.forename: Justin C
authors.initials: JC
authors.lastname: Crowley
authors.affiliation: Neuroimaging Laboratory, Department of Radiology, Department of Bioengineering, Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, USA and.
authors.forename: Seong-Gi
authors.initials: SG
authors.lastname: Kim
mesh_terms: D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002560:Cerebrovascular Circulation / Q000502:physiology*; D000075402:Channelrhodopsins; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000502:physiology*; D005552:Forelimb / Q000294:innervation*; D006439:Hemodynamics / Q000502:physiology*; D017078:Laser-Doppler Flowmetry; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009474:Neurons / Q000502:physiology; D010775:Photic Stimulation; D013003:Somatosensory Cortex / Q000098:blood supply* / Q000166:cytology / Q000502:physiology; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D000075402:Channelrhodopsins; D008164:Luminescent Proteins; C054562:yellow fluorescent protein, Bacteria
keywords: fMRI; hemodynamics; laminar activity; optogenetics; point spread function