title: Reliability and reproducibility of individual differences in functional connectivity acquired during task and resting state.
abstract: Application of fMRI connectivity metrics as diagnostic biomarkers at the individual level will require reliability, sensitivity and specificity to longitudinal changes in development, aging, neurocognitive, and behavioral performance and pathologies. Such metrics have not been well characterized for recent advances in BOLD acquisition.
  
  
  
  Analysis of multiband BOLD data from the HCP 500 Subjects Release was performed with FIX ICA and with WM, CSF and motion parameter regression. Analysis with ROIs covering the gray matter at 5 mm resolution was performed to assess functional connectivity. ROIs in key areas were used to demonstrate statistical differences between specific connections. Reproducibility of group-mean functional connectivity and for single connections for individuals was evaluated for both resting state and task acquisitions.
  
  
  
  Systematic differences in group-mean connectivity were demonstrated during task and rest and during different tasks, although individual differences in connectivity were maintained. Reproducibility of a single connection for a subject and across subjects for resting and task acquisition was demonstrated to be a linear function of the square root of imaging time. Randomly removing up to 50% of time points had little effect on reliability, while truncating an acquisition was associated with decreased reliability. Reliability was highest within the cortex, and lowest for deep gray nuclei, gray-white junction, and near large sulci.
  
  
  
  This study found systematic differences in group-mean connectivity acquired during task and rest acquitisions and preserved individual differences in connectivity due to intrinsic differences in an individual's brain activity and structural brain architecture. We also show that longer scan times are needed to acquire data on single subjects for information on connections between specific ROIs. Longer scans may be facilitated by acquisition during task paradigms, which will systematically affect functional connectivity but may preserve individual differences in connectivity on top of task modulations.
authors.affiliation: Department of Radiology University of Utah Salt Lake City Utah 84132.
authors.forename: Lubdha M
authors.initials: LM
authors.lastname: Shah
authors.affiliation: Department of Radiology University of Utah Salt Lake City Utah 84132.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Cramer
authors.affiliation: Department of Bioengineering University of Utah Salt Lake City Utah 84132.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Ferguson
authors.affiliation: Department of Psychiatry University of Wisconsin Madison Wisconsin 53705.
authors.forename: Rasmus M
authors.initials: RM
authors.lastname: Birn
authors.affiliation: Department of Radiology University of Utah Salt Lake City Utah 84132; Department of Bioengineering University of Utah Salt Lake City Utah 84132.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Anderson
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D063132:Connectome / Q000379:methods / Q000592:standards*; D005260:Female; D006801:Humans; D007206:Individuality; D008279:Magnetic Resonance Imaging / Q000379:methods / Q000592:standards*; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D015203:Reproducibility of Results; D055815:Young Adult
keywords: Functional connectivity; resting state fMRI reproducibility