title: Relative latency and temporal variability of hemodynamic responses at the human primary visual cortex.
abstract: The blood-oxygen-level-dependent (BOLD) functional MRI (fMRI) signal is a robust surrogate for local neuronal activity. However, it has been shown to vary substantially across subjects, brain regions, and repetitive measurements. This variability represents a limit to the precision of the BOLD response and the ability to reliably discriminate brain hemodynamic responses elicited by external stimuli or behavior that are nearby in time. While the temporal variability of the BOLD signal at human visual cortex has been found in the range of a few hundreds of milliseconds, the spatial distributions of the average and standard deviation of this temporal variability have not been quantitatively characterized. Here we use fMRI measurements with a high sampling rate (10Hz) to map the latency, intra- and inter-subject variability of the evoked BOLD signal in human primary (V1) visual cortices using an event-related fMRI paradigm. The latency relative to the average BOLD signal evoked by 30 stimuli was estimated to be 0.03±0.20s. Within V1, the absolute value of the relative BOLD latency was found correlated to intra- and inter-subject temporal variability. After comparing these measures to retinotopic maps, we found that locations with V1 areas sensitive to smaller eccentricity have later responses and smaller inter-subject variabilities. These correlations were found from data with either short inter-stimulus interval (ISI; average 4s) or long ISI (average 30s). Maps of the relative latency as well as inter-/intra-subject variability were found visually asymmetric between hemispheres. Our results suggest that the latency and variability of regional BOLD signal measured with high spatiotemporal resolution may be used to detect regional differences in hemodynamics to inform fMRI studies. However, the physiological origins of timing index distributions and their hemispheric asymmetry remain to be investigated.
authors.affiliation: Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan; Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland.
authors.forename: Fa-Hsuan
authors.initials: FH
authors.lastname: Lin
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Charlestown, MA 02129, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Polimeni
authors.affiliation: Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Jo-Fu Lotus
authors.initials: JL
authors.lastname: Lin
authors.affiliation: Aim for the Top University Project Office, National Taiwan Normal University, Taipei, Taiwan.
authors.forename: Kevin W-K
authors.initials: KW
authors.lastname: Tsai
authors.affiliation: Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Ying-Hua
authors.initials: YH
authors.lastname: Chu
authors.affiliation: Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Pu-Yeh
authors.initials: PY
authors.lastname: Wu
authors.affiliation: Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Yi-Tien
authors.initials: YT
authors.lastname: Li
authors.affiliation: Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Yi-Cheng
authors.initials: YC
authors.lastname: Hsu
authors.affiliation: Institute of Applied Physics, National Chengchi University, Taipei, Taiwan; Research Center for Mind Brain and Learning, National Chengchi University, Taipei, Taiwan.
authors.forename: Shang-Yueh
authors.initials: SY
authors.lastname: Tsai
authors.affiliation: Institute of Neuroscience, National Yang-Ming University, 155 Sec. 2, Li-Nung Street, Taipei 112, Taiwan. Electronic address: wjkuo@ym.edu.tw.
authors.forename: Wen-Jui
authors.initials: WJ
authors.lastname: Kuo
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult
keywords: Hemodynamics; Precision; Retinotopy; Stability; V1; fMRI