Voltage imaging in vivo

Abstract

Recent years have witnessed prosperous developments in tools and technologies expanding the optogenetic toolbox for monitoring and controlling neuronal activity. These developments enhanced mesoscopic optical imaging approach using genetically encoded activity indicators to allow population-specific chronic imaging experiments with high spatial coverage. Of these indicators, genetically encoded voltage indicators (GEVIs) offers the capability to directly read out neuronal electrical activity with high temporal resolution, and reports subthreshold activity – including hyperpolarising activity – in addition to spiking activity. However, there are still technical challenges uniquely associated with GEVI-based voltage imaging in the mammalian brain. This thesis outlines a series of explorations centred around GEVI-based voltage imaging in vivo in the mouse brain. First, I briefly describe a series of experiments using widefield mesoscopic GEVI imaging to monitor cortex-wide activity during somatosensory processing across different brain states. I highlight a technical consideration, namely the presence of haemodynamic components in the optical signals related to imaging in the green-red wavelength spectra. Next, I describe an approach combining fluorescence and reflectance imaging to correct for haemodynamic influence in widefield optical imaging data, and offer some initial physiological explorations using these data. Lastly, I describe an alternative approach, to bypass the haemodynamic signal component by using a novel GEVI we developed to optically image in the near-infrared wavelength range. Together, these explorations may provide some small inspirations for future endeavours towards realising the full capability of optical mesoscopic GEVI voltage imaging in vivo.