Awake Mouse Imaging: from 2-photon Microscopy to Blood Oxygen Level Dependent fMRI

This study provides a proof-of-principle demonstration for using chronic optical cranial windows in both animal Blood Oxygen Level Dependent (BOLD) fMRI studies and multimodal optical imaging, including 2-photon microscopy throughout the cortical depth. Following behavioral training, animals were imaged using two-photon microscopy for single-vessel diameter measurements, optogenetic study, spectral and laser speckle (LS) contrast imaging to measure blood oxygenation and flow, and BOLD fMRI for imaging global events.

The light microscopy images were obtained using an Ultima two-photon laser scanning microscopy system (Bruker) equipped with an Ultra II femtosecond Ti:Sapphire laser (Coherent) tuned between 800-1000 nm. The BOLD fMRI images were acquired on a 7T/11 cm horizontal bore scanner (BioSpec 70/20 USR).

For the future, this protocol can be extended to include more complex cognitive behaviors translatable to humans, such as sensory discrimination or attention. The ability to perform such studies, while alternating between imaging modalities and manipulating neuronal activity with optogenetic tools, can also facilitate neurophysiological underpinning of spontaneous (“resting state”) hemodynamic fluctuations, as well as cortical MRI signals in response to clinically-relevant perturbations of brain activity, for example in studies of stroke.