Head-mounted, high-speed confocal imager for voltage-sensitive neuronal recording

Project Summary/Abstract Cognitive functions of the brain are underpinned by complex and highly dynamic neural activities at the sub-cellular levels and millisecond time scales. To discover the normal/abnormal neuronal activities and thus understand detailed mechanisms of neurological disorders and dysfunctions such as Alzheimer’s, Parkinson’s disease and ALS (amyotrophic lateral sclerosis), measurement tools that offer sufficient spatiotemporal resolution are needed. Fluorescence imaging/microscopy is one of the state-of-the-art technologies for high spatial resolution recording of the activity of neuron populations. However, existing fluorescence neural imaging technologies generally have limited speed, providing less than a few hundred frames per second at most. High-speed imaging is particularly challenging for miniaturized, head-mounted imagers used for in vivo studies on freely-behaving animals. The milliseconds or slower temporal resolution substantially precludes measuring the precise timing of the generation and propagation of neuron spikes, which is the key component of neural signaling. Moreover, current head-mounted fluorescence imagers use epi-fluorescence illumination, which cannot reject out-of-focus background fluorescence, resulting in low discrimination of voltage-sensitive signals from the thin membranes of individual neurons. During this R&D program, Physical Sciences Inc. (PSI) and the Broad Institute of MIT and Harvard propose to develop and demonstrate a high-speed (>kHz frame rate), head-mounted, confocal imager that can optically capture neuronal electrical activity with high spatiotemporal details. Technology innovations are proposed to enable this capability. First, an “active sensing” signal detection method combines two complementary imaging channels to achieve parallel neuronal recording with both sub-micron spatial resolution and sub-millisecond temporal resolution. Second, a novel hybrid fiber bundle scanning approach achieves confocal imaging capability based on a miniaturized optical setup. During the proposed Phase I, we will demonstrate the feasibility of the technology by imaging cultured neurons and brain slices labeled with voltage fluorescent indicators. Then, we will upgrade the technology to a miniaturized imager to further demonstrate its performance during in vivo imaging of mice. These test experiments will demonstrate high spatiotemporal resolution recording of fast action potentials from individual neurons and sub-cellular neuron structures (e.g., dendrites and synapses). This R&D project will result in a robust technology for non- invasive recording of neuronal kinetics with high spatiotemporal resolution on freely-behaving animals, offering a critical tool for neuroscience research.