title: Investigating the wavelet coherence phase of the BOLD signal.
abstract: OBJECTIVE
  To investigate the temporal behavior of the blood oxygenation-level dependent (BOLD) signal applying the wavelet coherence phase to functional magnetic resonance imaging (fMRI) data.
  
  
  METHODS
  The wavelet coherence phase was computed for a group of four subjects using three functional runs of different visual stimulation lengths. In order to consider the variability of the wavelet coherence phase, a correlation analysis was performed between the variance of the phase shift and the associated activation strength. In activated brain regions, correlation was performed between the mean wavelet coherence phase and the spectral density phase shift.
  
  
  RESULTS
  The scalograms of the wavelet coherence phase show the temporal variability of the phase shift between fMRI time series. For brain regions with weakly stationary behavior, the mean wavelet coherence phase supports the results obtained by spectral analyses.
  
  
  CONCLUSIONS
  The wavelet coherence phase provides a description of the temporal behavior of the BOLD signal even for the nonstationary case. In particular, temporal changes of the phase shift can be investigated. This makes the wavelet coherence phase more suitable for the investigation of BOLD dynamics than an average phase lag obtained by correlation or spectral methods.
authors.affiliation: Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany. karstenm@cbs.mpg.de
authors.forename: Karsten
authors.initials: K
authors.lastname: Müller
authors.forename: Gabriele
authors.initials: G
authors.lastname: Lohmann
authors.forename: Jane
authors.initials: J
authors.lastname: Neumann
authors.forename: Maren
authors.initials: M
authors.lastname: Grigutsch
authors.forename: Toralf
authors.initials: T
authors.lastname: Mildner
authors.forename: D Yves
authors.initials: DY
authors.lastname: von Cramon
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D010100:Oxygen / Q000097:blood*; D010775:Photic Stimulation
chemical_list: D010100:Oxygen