Enhanced Image Sensor Module for Head-Mounted Microscopes.

Several research groups have developed head-mounted fluorescence microscopes as a modality for recording neural activity in freely behaving mice. The current designs have shown exciting results from in vivo imaging of the bright dynamics of genetically encoded calcium indicators (GECI). However, despite their potential, head-mounted microscopes are not in use with genetically encoded voltage indicators (GEVI) or bioluminescence indicators. Due to its ability to match the temporal resolution of neuron spiking, GEVIs offer great benefits to experiments designed to provide feedback after real-time detection of specific neural activity such as the less than 250ms replay events that can occur in the hippocampus. Orthogonally, the emerging bioluminescence activity reporters have the potential to eliminate autofluorescence and photobleaching that can occur in fluorescence imaging. There are two important properties of the head-mounted microscope's image sensor affecting the ability to image GEVIs and bioluminescence indicators. First, the low signal to noise ratio (SNR) characteristics of GEVIs and bioluminescent indicators make signal detection difficult. Second, in order to take advantage of the GEVIs faster fluorescence kinetics, the image sensor must be capable of matching frame rates. Here, we present the design of a new imaging module for head-mounted microscopes incorporating the latest CMOS sensor technology aimed at increasing image sensor sensitivity and frame rates for use in real-time detection experiments. The design builds off an existing open-source project and can integrate into the existing data acquisition hardware and microscope housing.