In vivo widefield calcium imaging of the mouse cortex for analysis of network connectivity in health and brain disease

• Published in: NeuroImage (Orlando, Fla.) Fla.), 2019-10, Vol.199, p.570-584
• Main Authors: Cramer, Julia V., Gesierich, Benno, Roth, Stefan, Dichgans, Martin, Düring, Marco, Liesz, Arthur
• Format: Article
• Language: English
• Subjects: Algorithms; Anesthesia; Animal models; Animals; Brain architecture; Brain diseases; Brain injury; Brain mapping; Brain research; Calcium; Calcium imaging; Cerebral Cortex - diagnostic imaging; Cerebral Cortex - physiology; Cerebral Cortex - physiopathology; Cerebral hemispheres; Connectome - methods; Cortex (motor); Disease; Disease Models, Animal; Female; Functional magnetic resonance imaging; ICA; In vivo imaging; Male; Mice; Mice, Inbred C57BL; Motor Cortex - injuries; Motor Cortex - physiopathology; Mouse models; Nerve Net - diagnostic imaging; Nerve Net - physiology; Nerve Net - physiopathology; Nervous system; Neural networks; Neuroimaging; Neuroimaging - methods; Neuronal network connectivity; Optical Imaging - methods; Prosencephalon - diagnostic imaging; Prosencephalon - physiology; Prosencephalon - physiopathology; Recovery; Stroke; Stroke - diagnostic imaging; Stroke - physiopathology; Traumatic brain injury
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2019.06.014

The organization of brain areas in functionally connected networks, their dynamic changes, and perturbations in disease states are subject of extensive investigations. Research on functional networks in humans predominantly uses functional magnetic resonance imaging (fMRI). However, adopting fMRI and other functional imaging methods to mice, the most widely used model to study brain physiology and disease, poses major technical challenges and faces important limitations. Hence, there is great demand for alternative imaging modalities for network characterization. Here, we present a refined protocol for in vivo widefield calcium imaging of both cerebral hemispheres in mice expressing a calcium sensor in excitatory neurons. We implemented a stringent protocol for minimizing anesthesia and excluding movement artifacts which both imposed problems in previous approaches. We further adopted a method for unbiased identification of functional cortical areas using independent component analysis (ICA) on resting-state imaging data. Biological relevance of identified components was confirmed using stimulus-dependent cortical activation. To explore this novel approach in a model of focal brain injury, we induced photothrombotic lesions of the motor cortex, determined changes in inter- and intrahemispheric connectivity at multiple time points up to 56 days post-stroke and correlated them with behavioral deficits. We observed a severe loss in interhemispheric connectivity after stroke, which was partially restored in the chronic phase and associated with corresponding behavioral motor deficits. Taken together, we present an improved widefield calcium imaging tool accounting for anesthesia and movement artifacts, adopting an advanced analysis pipeline based on human fMRI algorithms and with superior sensitivity to recovery mechanisms in mouse models compared to behavioral tests. This tool will enable new studies on interhemispheric connectivity in murine models with comparability to human imaging studies for a wide spectrum of neuroscience applications in health and disease. •We established a widefield in vivo imaging approach for cortical, neuronal activity.•This tool allows network connectivity analyses comparable to fMRI studies.•We determined an optimized sedation protocol to minimize anesthesia effects.•Experimental stroke induces long-term changes in cortical network function.•This tool is superior to behavior test for monitoring post-stroke recovery.