title: All-Optical Interrogation of Neural Circuits.
abstract: There have been two recent revolutionary advances in neuroscience: First, genetically encoded activity sensors have brought the goal of optical detection of single action potentials in vivo within reach. Second, optogenetic actuators now allow the activity of neurons to be controlled with millisecond precision. These revolutions have now been combined, together with advanced microscopies, to allow "all-optical" readout and manipulation of activity in neural circuits with single-spike and single-neuron precision. This is a transformational advance that will open new frontiers in neuroscience research. Harnessing the power of light in the all-optical approach requires coexpression of genetically encoded activity sensors and optogenetic probes in the same neurons, as well as the ability to simultaneously target and record the light from the selected neurons. It has recently become possible to combine sensors and optical strategies that are sufficiently sensitive and cross talk free to enable single-action-potential sensitivity and precision for both readout and manipulation in the intact brain. The combination of simultaneous readout and manipulation from the same genetically defined cells will enable a wide range of new experiments as well as inspire new technologies for interacting with the brain. The advances described in this review herald a future where the traditional tools used for generations by physiologists to study and interact with the brain-stimulation and recording electrodes-can largely be replaced by light. We outline potential future developments in this field and discuss how the all-optical strategy can be applied to solve fundamental problems in neuroscience.
  
  
  CONCLUSIONS
  This review describes the nexus of dramatic recent developments in optogenetic probes, genetically encoded activity sensors, and novel microscopies, which together allow the activity of neural circuits to be recorded and manipulated entirely using light. The optical and protein engineering strategies that form the basis of this "all-optical" approach are now sufficiently advanced to enable single-neuron and single-action potential precision for simultaneous readout and manipulation from the same functionally defined neurons in the intact brain. These advances promise to illuminate many fundamental challenges in neuroscience, including transforming our search for the neural code and the links between neural circuit activity and behavior.
authors.affiliation: Neurophotonics Laboratory, CNRS UMR 8250, Paris Descartes University, 75270 Paris Cedex 06, France, valentina.emiliani@parisdescartes.fr cohen@chemistry.harvard.edu deissero@stanford.edu m.hausser@ucl.ac.uk.
authors.forename: Valentina
authors.initials: V
authors.lastname: Emiliani
authors.affiliation: Departments of Chemistry and Chemical Biology and Physics, Howard Hughes Medical Institute and Harvard University, Cambridge, Massachusetts 02138, valentina.emiliani@parisdescartes.fr cohen@chemistry.harvard.edu deissero@stanford.edu m.hausser@ucl.ac.uk.
authors.forename: Adam E
authors.initials: AE
authors.lastname: Cohen
authors.affiliation: Department of Bioengineering and Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, and valentina.emiliani@parisdescartes.fr cohen@chemistry.harvard.edu deissero@stanford.edu m.hausser@ucl.ac.uk.
authors.forename: Karl
authors.initials: K
authors.lastname: Deisseroth
authors.affiliation: Wolfson Institute for Biomedical Research and Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom valentina.emiliani@parisdescartes.fr cohen@chemistry.harvard.edu deissero@stanford.edu m.hausser@ucl.ac.uk.
authors.forename: Michael
authors.initials: M
authors.lastname: Häusser
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology*; D006801:Humans; D009415:Nerve Net / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D062308:Optogenetics
keywords: calcium imaging; genetically encoded calcium sensor; genetically encoded voltage sensor; optogenetics; two-photon microscopy; wavefront shaping