2026 Theses Doctoral

Widefield Optical Imaging and Its Applications in Functional Connectivity and Glioma

Lodgher, Fatema

The brain is the organ through which we observe, interpret, and participate in life, and its healthy functioning is essential to keeping organisms alive. Understanding how healthy brains function gives us a basis to identify changes because of disease. Since brain neural activity is highly dependent on blood flow and healthy neurovascular coupling for optimal function, it is essential to accurately measure neuronal and hemodynamic activity.

Existing techniques are limited in spatial and temporal resolution or are unable to capture both neural activity and changes in blood flow simultaneously. One technique, electroencephalography (EEG), is commonly used to measure neural activity in the brain. Although fast enough to record real-time brain activity, EEGs are often spatially imprecise. They are often combined with functional magnetic resonance imaging (fMRI) to spatially identify where neural activity happens in the brain. However, fMRI measures blood flow as a proxy for neural activity. Since hemodynamics is slower than neural activity, fMRI loses temporal resolution. Although these techniques are used in tandem to balance out each other’s limitations, an approach that measures brain activity with high temporal and spatial resolution would be advantageous.

This present work utilizes wide-field optical mapping (WFOM) to measure neural activity and hemodynamics simultaneously in awake, behaving mice that express calcium indicators in select neuronal populations.

Using our single-color WFOM system, which measures hemodynamics and one calcium indicator, we measured cortical activity in a cohort of healthy mice to characterize network-level patterns that were dependent on behaviors. We used functional connectivity, an fMRI technique that identifies temporally dependent brain regions, to identify regions that consistently worked together through Pearson’s correlation. These correlated regions, or networks, were bilateral. We also saw that the correlation strengths of the networks with the rest of the cortex change because of behavior. During segments with mostly locomotion, the cortex exhibits high correlations of neural activity across most brain regions. In segments with only rest, the cortical networks exhibited low correlations across the cortex, except with their bilateral partner. This was a data driven way of identifying bilateral neural networks across the cortex and their relationship with each other during different behaviors in healthy mice.

Since we have a data-driven way to understand activity in the healthy brain, we next examined how disease states disrupt these activity patterns. We then expand on a previous study that used the single color WFOM system to examine the impact of glioma tumor growth on neural and hemodynamic activity using a GCaMP expressing mouse with glioma. This study found increased neural desynchronization and hemodynamic disruption in the cortex with tumor growth. From this, we became interested in understanding the relationship between neural activity, hemodynamics, and tumor activity in the cortex. To study this, a dual color WFOM system was developed to simultaneously image the changes in neural activity and tumor activity, along with hemodynamics in the mouse cortex.

We modified our WFOM system to include an image splitter that could separate the emission signals of two calcium indicators, jRGECO and GCaMP, in addition to reflectance measurements of hemodynamics. This system was validated and then used to image mice expressing jRGECO1a in excitatory neurons that were also injected with glioma expressing GCaMP6s.

In our preliminary analysis, this series of experiments using a dual color WFOM system revealed an increase in tumor signal overlapping with areas of neuronal signal reduction. We also see correlations between the tumor and neural activities, indicating a temporal relationship between tumor activity and neural activity.