Laminar differences in functional oxygen metabolism in monkey visual cortex measured with calibrated fMRI

Area of Science:

• Neuroimaging
• Metabolic imaging
• Functional neuroanatomy

Background:

• Blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) is limited by its bias towards large cortical veins.
• Functional changes in cerebral metabolic rate of oxygen (ΔCMRO2) may provide a more accurate measure of neural activity.
• The validity of the calibrated BOLD model for measuring ΔCMRO2 at high resolution remains uncertain.

Purpose of the Study:

• To investigate the feasibility and validity of laminar ΔCMRO2 measurements at high resolution.
• To compare laminar ΔCMRO2 with BOLD fMRI for assessing neural activity.
• To determine the laminar profile of ΔCMRO2 in response to visual stimulation.

Main Methods:

• Laminar ΔCMRO2 was measured using a calibrated BOLD model during visual stimulation in macaque primary visual cortex (V1).
• Autoradiographic measures of metabolism were used for comparison.
• The spatial distribution of ΔCMRO2 was analyzed in relation to cortical layers and surface veins.

Main Results:

• ΔCMRO2 peaked in the middle of the cortex, aligning with autoradiographic findings.
• Gray matter ΔCMRO2 values were consistent with previous studies.
• Reductions in CMRO2 were observed near cortical surface veins, suggesting potential improvements with vein removal techniques.

Conclusions:

• Laminar ΔCMRO2 measurement is feasible and provides a physiologically meaningful metric of functional metabolism.
• ΔCMRO2 offers a promising alternative to BOLD fMRI for high-resolution laminar neuroimaging.
• Further refinement of vein removal techniques could enhance the accuracy of high-resolution ΔCMRO2 measurements.