Ultrafast wireless voltage imaging with event-based cameras - PROJECT SUMMARY Information in the brain is encoded in the membrane potential variations of neurons. To understand the neural substrates of complex behaviors we need advanced methods that can capture such variations across large volumes, with high precision and in animals behaving naturally. Voltage imaging techniques are emerging as powerful tools towards these goals. They rely on the use of voltage sensitive molecules, that change their light emission properties upon changes in transmembrane voltage, coupled with imaging devices capable of collecting these localized signals. However, since physiologically relevant voltage signals can be extremely fast and distributed across large volumes, standard frame-based imaging sensors struggle to faithfully acquire them at sufficient temporal resolution and across large fields-of-view (FOVs). Moreover, the typical data bandwidth during voltage imaging with conventional sensors is hardly compatible with wireless applications. Here, to overcome these limitations, we propose to use a radically new type of sensors: event-based cameras (ECs). ECs are inspired by biological systems: rather than capturing images at a fixed rate, they asynchronously detect changes in brightness at each pixel, generating a continuous stream of events – analogous to action potentials - that encode the time, location, and polarity of these changes. Compared to conventional cameras, ECs have exceptional temporal resolution, low latency (both at the µs scale), extensive dynamic range (~120 dB), minimal power consumption (few mW) and reduced data output. However, the potential of ECs for imaging biologically relevant signals, such as calcium or voltage in neurons, remains virtually unexplored, as new methods are needed to acquire and process their output and embed ECs in current microscopes. Our proposal aims at pioneering the use of ECs for ultrafast voltage imaging across large FOVs. We will first investigate the capabilities of ECs for recording single action potentials across large FOVs (1 mm2) in neuronal cultures expressing genetically encoded voltage indicators (GEVIs). Second, we will set up and optimize the methods for imaging voltage signals with ECs in vivo, in the cortex and hippocampus of head-immobilized bats. Third, we will embed an ultra-compact event-based sensor into an existing miniaturized microscope for wireless one-photon voltage imaging. We will showcase the applicability of this new tool for untethered imaging by monitoring neural activity in the hippocampus of freely flying Egyptian fruit bats. Supporting the feasibility of this proposal, we have extensive expertise in wireless neural recordings in freely flying bats and we have collected preliminary data suggesting that ECs can capture voltage signals in vitro. Despite the highly ambitious nature of this project, we believe it will make several groundbreaking contributions to the rapidly expanding fields of event-based sensing and biomedical fluorescence imaging.
