Does the Cortical-Depth Dependence of the Hemodynamic Response Function Differ Between Age Groups?

Area of Science:

• Neuroimaging
• Human Brain Function

Background:

• Functional magnetic resonance imaging (fMRI) is crucial for studying brain activity.
• Blood-oxygen-level-dependent (BOLD) hemodynamic response function (HRF) consistency is vital for valid fMRI comparisons.
• HRF varies across individuals, brain regions, and cortical depth, challenging standard assumptions.

Purpose of the Study:

• To investigate age-related changes in HRF properties as a function of cortical depth.
• To assess the impact of age on HRF magnitude and temporal dynamics in the primary visual cortex (V1).

Main Methods:

• Utilized 7 Tesla (7T) fMRI with ultra-high spatiotemporal resolution line-scanning (250 μm, 105 ms sampling).
• Estimated HRFs using smooth basis function deconvolution in 11 young and 11 middle-aged healthy participants.
• Compared HRF properties derived from high-resolution line-scanning with conventional fMRI resolutions.

Main Results:

• Cortical depth-dependent HRFs were comparable to those obtained with conventional resolutions, validating the approach.
• HRF properties, including magnitude and temporal dynamics, showed no significant differences between young and middle-aged groups across cortical depth.
• Inter-individual variability in HRF properties exceeded age-group differences.

Conclusions:

• HRF properties in the primary visual cortex do not significantly differ between young and middle-aged adults.
• Middle-aged individuals can participate in cortical depth-dependent fMRI studies without introducing bias related to HRF properties.
• High-resolution fMRI line-scanning is a valid method for investigating laminar HRF variations.