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Related Experiment Videos

The spatial extent of the BOLD response.

Ziad S Saad1, Kristina M Ropella, Edgar A DeYoe

  • 1Laboratory of Brain and Cognition, National Institute of Mental Health, NIH, Bethesda, MD 20892-1148, USA. ziad@nih.gov

Neuroimage
|June 5, 2003
PubMed
Summary

Averaging multiple functional magnetic resonance imaging (fMRI) scans reveals more brain activation than expected, with activation volume increasing with more averaging. Many low-signal voxels are detected with extensive averaging.

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Area of Science:

  • Neuroimaging
  • Cognitive Neuroscience

Background:

  • Functional magnetic resonance imaging (fMRI) is standard for brain function localization.
  • Averaging multiple scans enhances signal-to-noise ratio (SNR) for activation volumes.

Purpose of the Study:

  • To investigate the impact of multiple scan averaging on fMRI activation volume extent.
  • To identify factors contributing to changes in activation volume with averaging.

Main Methods:

  • Used restricted visual field stimulation with numerous scan repetitions.
  • Analyzed activation volume changes with progressive averaging and across single scans.
  • Employed empirical and simulated data for analysis.

Main Results:

  • Activation volume increased monotonically with averaging up to 22 scans.

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  • Spatial expansion of activation was centered around initial loci.
  • Revealed more activated voxels, many with low SNR, undetected without averaging.
  • Identified low SNR voxels likely due to diffuse subthreshold activity or extended blood flow response, not venous drainage.

    • Conclusions:

    • Extensive averaging in fMRI is crucial for detecting low-SNR activation, revealing a larger functional volume than commonly assumed.
    • Single-scan variability in activation volume suggests complex signal and noise interactions.