title: Task Dependence, Tissue Specificity, and Spatial Distribution of Widespread Activations in Large Single-Subject Functional MRI Datasets at 7T.
abstract: It was recently shown that when large amounts of task-based blood oxygen level-dependent (BOLD) data are combined to increase contrast- and temporal signal-to-noise ratios, the majority of the brain shows significant hemodynamic responses time-locked with the experimental paradigm. Here, we investigate the biological significance of such widespread activations. First, the relationship between activation extent and task demands was investigated by varying cognitive load across participants. Second, the tissue specificity of responses was probed using the better BOLD signal localization capabilities of a 7T scanner. Finally, the spatial distribution of 3 primary response types--namely positively sustained (pSUS), negatively sustained (nSUS), and transient--was evaluated using a newly defined voxel-wise waveshape index that permits separation of responses based on their temporal signature. About 86% of gray matter (GM) became significantly active when all data entered the analysis for the most complex task. Activation extent scaled with task load and largely followed the GM contour. The most common response type was nSUS BOLD, irrespective of the task. Our results suggest that widespread activations associated with extremely large single-subject functional magnetic resonance imaging datasets can provide valuable information about the functional organization of the brain that goes undetected in smaller sample sizes.
authors.affiliation: Section on Functional Imaging Methods, Laboratory of Brain and Cognition.
authors.forename: Javier
authors.initials: J
authors.lastname: Gonzalez-Castillo
authors.affiliation: Section on Functional Imaging Methods, Laboratory of Brain and Cognition.
authors.forename: Colin W
authors.initials: CW
authors.lastname: Hoy
authors.affiliation: Section on Functional Imaging Methods, Laboratory of Brain and Cognition.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Handwerker
authors.affiliation: Functional MRI Facility.
authors.forename: Vinai
authors.initials: V
authors.lastname: Roopchansingh
authors.affiliation: Functional MRI Facility.
authors.forename: Souheil J
authors.initials: SJ
authors.lastname: Inati
authors.affiliation: Scientific and Statistical Computing Core, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Ziad S
authors.initials: ZS
authors.lastname: Saad
authors.affiliation: Scientific and Statistical Computing Core, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Cox
authors.affiliation: Section on Functional Imaging Methods, Laboratory of Brain and Cognition Functional MRI Facility.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Bandettini
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D003627:Data Interpretation, Statistical; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D066128:Gray Matter / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012107:Research Design; D014796:Visual Perception / Q000502:physiology; D055815:Young Adult
keywords: activation extent; negative BOLD; single subject; transients