Simultaneous fMRI and fluorescence calcium imaging of brain dynamics under hypercapnia in mice

Motivation: Hypercapnia-induced changes in neurovascular coupling are not well understood. Goal(s): Our goal was to capture and differentiate the neural and hemodynamic effects of hypercapnia. Approach: We used concurrent fMRI and fluorescence calcium imaging in mice under elevated CO₂, analyzing spatiotemporal patterns of functional connectivity across modalities. Results: Findings showed a distinct decoupling between neural and vascular responses under hypercapnia. Notably, BOLD signals did not transition into a neural state, remaining in a baseline vascular mode with significantly dampened fluorescence-triggered responses. In contrast, FL signals transitioned into the neural mode more frequently, revealing adaptive shifts in neural dynamics under hypercapnic stress. Impact: By differentiating neural and vascular responses under hypercapnia, this study highlights limitations of BOLD as a neural marker during CO₂ stress. Findings inform strategies to restore neurovascular balance, relevant to chronic hypercapnic disorder diagnosis and treatment.