title: Local and global contributions to hemodynamic activity in mouse cortex.
abstract: Imaging techniques such as functional magnetic resonance imaging seek to estimate neural signals in local brain regions through measurements of hemodynamic activity. However, hemodynamic activity is accompanied by large vascular fluctuations of unclear significance. To characterize these fluctuations and their impact on estimates of neural signals, we used optical imaging in visual cortex of awake mice. We found that hemodynamic activity can be expressed as the sum of two components, one local and one global. The local component reflected presumed neural signals driven by visual stimuli in the appropriate retinotopic region. The global component constituted large fluctuations shared by larger cortical regions, which extend beyond visual cortex. These fluctuations varied from trial to trial, but they did not constitute noise; they correlated with pupil diameter, suggesting that they reflect variations in arousal or alertness. Distinguishing local and global contributions to hemodynamic activity may help understand neurovascular coupling and interpret measurements of hemodynamic responses.
authors.affiliation: Institute of Ophthalmology, University College London, London, United Kingdom.
authors.forename: M Andrea
authors.initials: MA
authors.lastname: Pisauro
authors.affiliation: Institute of Ophthalmology, University College London, London, United Kingdom.
authors.forename: Andrea
authors.initials: A
authors.lastname: Benucci
authors.affiliation: Institute of Ophthalmology, University College London, London, United Kingdom m.carandini@ucl.ac.uk.
authors.forename: Matteo
authors.identifier: 0000-0003-4880-7682
authors.initials: M
authors.lastname: Carandini
mesh_terms: D000818:Animals; D053483:Eye Movement Measurements; D005133:Eye Movements / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D008297:Male; D008810:Mice, Inbred C57BL; D061848:Optical Imaging; D010775:Photic Stimulation; D011680:Pupil / Q000502:physiology; D014793:Visual Cortex / Q000098:blood supply* / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology
keywords: brain imaging; hemodynamic activity; neurovascular coupling