title: Cortical depth dependence of the BOLD initial dip and poststimulus undershoot in human visual cortex at 7 Tesla.
abstract: OBJECTIVE
  Owing to variability in vascular dynamics across cerebral cortex, blood-oxygenation-level-dependent (BOLD) spatial and temporal characteristics should vary as a function of cortical-depth. Here, the positive response, initial dip (ID), and post-stimulus undershoot (PSU) of the BOLD response in human visual cortex are investigated as a function of cortical depth and stimulus duration at 7 Tesla (T).
  
  
  METHODS
  Gradient-echo echo-planar-imaging BOLD fMRI with high spatial and temporal resolution was performed in 7 healthy volunteers and measurements of the ID, PSU, and positive BOLD response were made as a function of cortical depth and stimulus duration (0.5-8 s). Exploratory analyses were applied to understand whether functional mapping could be achieved using the ID, rather than positive, BOLD signal characteristics
  
  
  RESULTS
  The ID was largest in outer cortical layers, consistent with previously reported upstream propagation of vasodilation along the diving arterioles in animals. The positive BOLD signal and PSU showed different relationships across the cortical depth with respect to stimulus duration.
  
  
  CONCLUSIONS
  The ID and PSU were measured in humans at 7T and exhibited similar trends to those recently reported in animals. Furthermore, while evidence is provided for the ID being a potentially useful feature for better understanding BOLD signal dynamics, such as laminar neurovascular coupling, functional mapping based on the ID is extremely difficult.
authors.affiliation: Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.|Rudolf Magnus Institute, Department of Neurosurgery and Neurology, University Medical Center Utrecht, The Netherlands.
authors.forename: Jeroen C W
authors.initials: JC
authors.lastname: Siero
authors.affiliation: Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Hendrikse
authors.affiliation: Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Hans
authors.initials: H
authors.lastname: Hoogduin
authors.affiliation: Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Natalia
authors.initials: N
authors.lastname: Petridou
authors.affiliation: Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: Luijten
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.|Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.|Psychiatry, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.|Neurology, Vanderbilt School of Medicine, Nashville, Tennessee, USA.|Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Manus J
authors.initials: MJ
authors.lastname: Donahue
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D002560:Cerebrovascular Circulation / Q000502:physiology; D017352:Echo-Planar Imaging; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010775:Photic Stimulation; D014793:Visual Cortex / Q000033:anatomy & histology*
keywords: BOLD; cortical depth; fMRI; hemodynamic response; initial dip; undershoot; vasodilation