Functional connectivity gradients depend on cortical sampling position and brain state

Area of Science:

• Neuroscience
• Functional Neuroimaging
• Brain Connectivity

Background:

• Functional connectivity analyses often assume nearby cortical signals are interchangeable.
• Anatomical and hemodynamic transitions exist at the gray-white boundary, potentially influencing signal interpretation.

Purpose of the Study:

• To investigate if sampling position (midthickness vs. gray-white boundary) is a state-sensitive dimension of macroscale functional organization.
• To determine how functional brain organization differs between resting-state and movie-watching conditions based on sampling position.

Main Methods:

• Acquired 7 Tesla resting-state and movie-watching BOLD data from 176 participants.
• Sampled time series from midthickness and gray-white boundary surfaces, summarized across cortical parcels.
• Analyzed functional gradients and used Shapley decomposition for state-change interpretation.

Main Results:

• Movie viewing reduced gradient separation between surfaces, with heterogeneous effects across brain networks.
• State changes reflected coordinated reconfiguration of both surface representations.
• Resting-state separation maps generalized across field strengths (7T to 3T), but magnitude and individual rankings varied.

Conclusions:

• Cortical sampling position is an interpretable dimension of functional connectivity geometry.
• Spatial organization is reproducible, but magnitude and state dependence vary.
• Signal sampling location relative to the cortical boundary influences conclusions about brain organization.