Abstract Signals in the brain are transmitted and transformed on a millisecond timescale. The precise timing of activity can carry unique information, correlate perceptual decisions, and powerfully influence synaptic plasticity. Therefore, to understand the circuits that generate behavior and the circuit changes responsible for learning, we must interrogate signaling in vivo at millisecond timescales. Since the advent of two-photon microscopy, these signals have primarily been inferred in vivo through the use of fluorescent indicators with far slower dynamics. Recently, neuroscientists have made impressive gains in developing genetically-encoded indicators of neural activity with millisecond dynamics. However, current two-photon technology limits high-fidelity recording of fast membrane-bound indicators to very few compartments and for relatively little time, representing a major barrier to collecting the simultaneous recordings we need to understand the circuits that control behavior. To overcome this barrier, we propose to leverage the unparalleled speed of light deflection through electro-optical crystals. Recent breakthroughs in electro-optical deflection have enabled large increases in deflection range and nanosecond response times. However, small aperture and temperature gradients in commercial devices still limit the performance of these deflectors. We propose an entirely new deflector design capable of deflecting larger laser beams at high speeds. We will use these new deflectors to develop a microscope capable of random-access multiphoton interrogation of neurons and synapses with sub-microsecond access times. This tool to image synaptic and cellular activity across networks of neurons will provide neuroscientists with critical information on the processes that implement computations in the brain, as well as the disruption of these processes in models of disease.

Project Narrative Neuroscientists have made impressive gains in developing fluorescent sensors to track the transmission and transformation of signals across neurons at millisecond timescales, however imaging these fast sensors in vivo remains challenging. We propose an ultrafast microscope based on electro-optical deflection technology to enable precise imaging of synaptic and spiking activity in vivo. This will provide a critical tool for understanding cellular and subcellular mechanisms of neural computation and their disruption in disease.