title: Disparity of activation onset in sensory cortex from simultaneous auditory and visual stimulation: Differences between perfusion and blood oxygenation level-dependent functional magnetic resonance imaging.
abstract: OBJECTIVE
  To compare the temporal behaviors of perfusion and blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in the detection of timing differences between distinct brain areas, and determine potential latency differences between stimulus onset and measurable fMRI signal in sensory cortices.
  
  
  METHODS
  Inversion recovery (IR) spin-echo echo-planar imaging (EPI) and T2*-weighted gradient-echo EPI sequences were used for perfusion- and BOLD-weighted experiments, respectively. Simultaneous auditory and visual stimulations were employed in an event-related (ER) paradigm. Signal time courses were averaged across 40 repeated trials to evaluate the onset of activation and to determine potential differences of activation latency between auditory and visual cortices and between these scanning methods.
  
  
  RESULTS
  Temporal differences between visual and auditory areas ranged from 90-200 msec (root-mean-square (RMS) = 134 msec) and from -80 to 930 msec (RMS = 604 msec) in perfusion and BOLD measurements, respectively. The temporal variability detected with BOLD sequences was larger between subjects and was significantly greater than that in the perfusion response (P < 0.04). The measured time to half maximum (TTHM) values for perfusion imaging (visual, 3260 +/- 710 msec; auditory, 3130 +/- 700 msec) were earlier than those in BOLD responses (visual, 3770 +/- 430 msec; auditory, 3360 +/- 460 msec).
  
  
  CONCLUSIONS
  The greater temporal variability between brain areas detected with BOLD could result from differences in the venous contributions to the signal. The results suggest that perfusion methods may provide more accurate timing information of neuronal activities than BOLD-based imaging.
authors.affiliation: MRI Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Ho-Ling
authors.initials: HL
authors.lastname: Liu
authors.forename: Ching-Mei
authors.initials: CM
authors.lastname: Feng
authors.forename: Jinqi
authors.initials: J
authors.lastname: Li
authors.forename: Fan-Chi
authors.initials: FC
authors.lastname: Su
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: David
authors.initials: D
authors.lastname: Glahn
authors.forename: Jia-Hong
authors.initials: JH
authors.lastname: Gao
mesh_terms: D000161:Acoustic Stimulation; D000465:Algorithms; D001303:Auditory Cortex / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D017352:Echo-Planar Imaging / Q000379:methods; D005071:Evoked Potentials / Q000502:physiology; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009474:Neurons / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D014793:Visual Cortex / Q000502:physiology*
chemical_list: D010100:Oxygen