Simultaneous single-cell calcium imaging of neuronal population activity and brain-wide BOLD fMRI

Blood Oxygen Level-Dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) allows for non-invasive, indirect recordings of neural activity across the whole brain in both humans and animals. However, the relationship between the local neural population activity and the vascular activity is not completely understood. To investigate this relationship, we present a novel MRI compatible single-photon microscope capable of measuring cellular resolution Ca2+ activity of genetically defined neurons during whole-brain BOLD fMRI in awake behaving mice. Using this combined imaging approach, we found a difference in activity patterns between cells which was dependent on their location with respect to the vasculature. Notably, neurons near the vasculature showed pronounced negative activity during contralateral whisker movements at 3 Hz. In a second proof of concept experiment, we demonstrate the potential of recording both local neural activities, like those in the barrel field (SSp-bfd), and BOLD fMRI readings from interlinked brain regions. In sum, the presented technological advancement paves the way for studies examining the interplay between local brain circuits and overarching brain functions. In addition, the new approach enhances our understanding of the vascular BOLD fMRI signal, providing insights into the determinants of local neurovascular functions and the brains organizational framework across various scales.