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Title : 10 years after ChR2 in --views from the community.

Permalink https://escholarship.org/uc/item/3wf9h6g2

Journal Nature neuroscience, 18(9)

ISSN 1097-6256

Authors Adamantidis, Antoine Arber, Silvia Bains, Jaideep S et al.

Publication Date 2015-09-01

DOI 10.1038/nn.4106

Peer reviewed

eScholarship.org Powered by the California Digital Library University of California Q&A

Optogenetics: 10 years after ChR2 in neurons—views from the community

Antoine Adamantidis, Silvia Arber, Jaideep S Bains, , Antonello Bonci, György Buzsáki, Jessica A Cardin, Rui M Costa, Yang Dan, Yukiko Goda, Ann M Graybiel, Michael Häusser, , John R Huguenard, Thomas R Insel, Patricia H Janak, Daniel Johnston, Sheena A Josselyn, Christof Koch, Anatol C Kreitzer, Christian Lüscher, Robert C Malenka, Gero Miesenböck, , Botond Roska, Mark J Schnitzer, Krishna V Shenoy, Ivan Soltesz, Scott M Sternson, Richard W Tsien, Roger Y Tsien, Gina G Turrigiano, Kay M Tye & Rachel I Wilson

On the anniversary of the Boyden et al. (2005) paper that introduced the use of in neurons, Nature Neuroscience asks selected members of the community to comment on the utility, impact and future of this important technique.

euroscientists have long dreamed of and applied to a vast array of questions both in technique has had on neuroscience, we were Nthe ability to control neuronal activ- neuroscience and beyond. curious to know how researchers in the field ity with exquisite spatiotemporal precision. In the intervening years, improvements to feel the advances in optogenetic approaches In this issue, we celebrate the tenth anniver- early techniques have provided the community have influenced their work, what they think sary of a paper published in the September with an optogenetics tool box that has opened the future holds in terms of the application 2005 issue of Nature Neuroscience by a team the door to experiments we could have once of these techniques and what they see as the led by (Nat. Neurosci. 8, only dreamed of. Controlling neuronal activity obstacles we need to overcome to get there. 1263–1268 (2005)). In this study, the authors in real time, we now have the ability to deter- Toward this end, we’ve asked a number of expressed a light-sensitive microbial protein, mine causality between activity patterns in spe- scientists to share their thoughts with us in Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature Channelrhodopsin-2 (ChR2), in neurons and cific neuronal circuits and function and this Q&A. Although we weren’t able to ask showed that exposing these neurons to pulses behavior, enabling researchers to definitively test more than a small fraction of the field, their of light could activate them in a temporally pre- long-held views and advance our understanding answers give an exciting view of the power and npg cise and reliable manner. In the decade since of brain function in both health and disease. potential of optogenetic approaches for under- this paper, ‘optogenetic’ approaches have been Anniversaries are often a time to reflect standing, and even potentially repairing, the widely and enthusiastically adopted by the field and, in light of the seminal influence this nervous system.

How do you define optogenetics? Ernst Bamberg: Optogenetics is the use of of genetically encoded molecules to excite and genetically encoded light-activated proteins inhibit neurons. I would prefer it to mean any John Huguenard: Sensitizing neurons to light, for manipulation of cells in an almost non- genetically encoded tool to record or perturb then manipulating neural activity in precise invasive way by light. The most prominent electrical activity of neurons and other excit- spatiotemporal patterns to answer questions tool is ChR2, which allows in a cell-specific able cells. But using a broad name to identify regarding neural circuits and behavior. way the activation of electrical excitable cells a fairly specific subset of tasks was a brilliant via the light-dependent depolarization. The stroke, nonetheless. Michael Häusser: There’s a broad definition combination of ChR2 with hyperpolarizing and a narrow definition. The broad defini- light-driven ion pumps such as the Cl- pump Dan Johnston: I suppose that the accurate tion is rooted in etymology: any approach that halorhodopsin (NphR) allows, with high tem- definition would be genetically encoded opti- combines optical interrogation with genetic poral and spatial precision, the activation or cal sensors, but it is most commonly thought of targeting qualifies as ‘optogenetic’, and that inactivation of neural cells in culture, tissue as genetically encoded light-activated channels. includes the use of genetically encoded activ- and living animals. It’s worth noting, however, and I wasn’t aware of ity sensors. However, most people generally it at the time I reviewed the Boyden paper, but use the term optogenetics to mean the use of Richard Tsien: This 10-year celebration, well- there were two papers that predated this one probes to manipulate activity, and (as is usual deserved by the authors and journal alike, that reported a genetically encoded light-acti- in English) usage normally wins. implicitly points to a narrower definition: use vated channel: Zemelman, B.V. et al. 33,

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15–22 (2002) and Zemelman, B.V. et al. Proc. would really work in the manners that were clear that the technique was very robust and rep- Natl. Acad. Sci. USA 100, 1352–1357 (2003). promised. I thought it might have some finite licable. Shortly thereafter I decided to do a post- uses, but did not imagine it would be as “revo- doc focusing on this approach, and that’s how I Mark Schnitzer: lutionary” as it turned out to be. ended up at Stanford with Karl Deisseroth. The term ‘optoge- netics’ first appeared Krishna Shenoy: I Antoine Adamantidis: At that time, I was in 2006 in a short had the great pleasure finishing my PhD at the University of Liege, review article pub- of being right here at Belgium, and we were investigating the role lished in Journal Stanford and know- of a unique popula- of Neuroscience to ing Ed and Karl for tion of neurons in the Mark Schnitzer accompany a Society years, so yes, when lateral hypothalamus for Neuroscience their results came in (that is, melanin- mini-symposium that Karl Deisseroth and I and the paper came Krishna Shenoy concentrating hor- had organized. (Deisseroth, K. et al. J. Neurosci. out it was clear it mone) in controlling 26, 10380–10386 (2006)). We considered differ- would be an enormous advance. Could I have ‘dream sleep’. In mam- ent options, such as ‘photogenetics’, but even- predicted how revolutionary it would be? mals, this deep sleep Antoine Adamantidis tually settled on optogenetics as the best term No, there I’m afraid I would have underesti- stage lasts classically to describe techniques that combined optical mated the full extent to which it has been a few minutes, which made it difficult to study and genetic facets. Notably, our original intent ­neuroscience-wide seismic shift! with conventional ‘low temporal’ approaches was to cover both genetically targeted optical (pharmacology, KO, KI, etc.) without altering control and imaging under a single umbrella Sheena Josselyn: I thought the data were other sleep stages. Thus, when the Boyden/ term. Nevertheless, I have subsequently always interesting, but likely not replicable and defi- Deisseroth publication came out, I thought, preferred a narrower interpretation of optoge- nitely not generalizable. I thought optogenet- “This is it! That’s what we need!” Since I was netics that covers only the control approaches ics would not work reliably and, even if it did, joining the laboratory of Professor Luis de and the wonderful field that grew out of Karl’s the technique would be so complicated as to Lecea at Stanford University a few months later, seminal 2005 paper in Nature Neuroscience; be out of reach for most neuroscience labs. My I emailed Karl about this idea, who replied, “OK, the broader interpretation of optogenetics that initial impression was that optogenetics would let’s meet when you get here!” We did meet, includes imaging is so general that, in some be highly parameter-sensitive and would take and, together with Dr. , brought it respects, it can be vague. My impression is that lots of fiddling to get any kind of effect. I was to brain slices and freely moving mice to publish a substantial majority of the usages of the term definitely in the camp that didn’t think it would the first in vivo optogenetic paper establishing optogenetics in the neuroscience literature fol- have an impact on my kind of neuroscience. a causal role between hypocretin/orexin cells lows the narrower interpretation. and arousal (Adamantidis, A. et al., Nature 450, Scott Sternson: I thought that if it worked as 420–424 (2007)). Thus, yes, I believe this was a Rachel Wilson: I think of optogenetic tools as advertised, then it would be exactly the tool transformative technology since early on! a set of wrenches in a larger toolkit of geneti- that I’d been looking for since I started in neu- cally encoded effec- roscience. Thomas Insel: While everyone assumes opto- Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature tors. This includes genetics is a great technology, reviewers on NIH effectors activated Gina Turrigiano: Intense excitement. I study sections in 2005 by heat, as well as thought the work leading up to this study was did not embrace this npg effectors activated by a beautiful example of basic curiosity-driven idea. Fortunately, a designer drugs, etc. research (trying to understand the basis of very smart program Optogenetic tools are bacterial phototaxis) leading to an unantici- officer at NIMH rec- Rachel Wilson often the most useful pated transformative outcome. ognized the promise because light can be of this proposal. And modulated so rapidly and precisely. However, Kay Tye: My first Thomas Insel soon after this first we should just reach for the tool that suits the reaction was one of NIMH K award, the job. Sometimes the old tools are best! wonder and amaze- advent of the Pioneer Awards, designed for high ment. Seriously? Is risk–high reward research, gave Karl the kind What was your first reaction when this really possible? I of support needed to take this from concept to optogenetics came onto the scene was a junior gradu- tool. Optogenetics was a great object lesson for 10 years ago? Did you think it would ate student at the NIH, revealing the need for mechanisms like have such a transformative impact on Kay Tye time and it was quite the Pioneer Award that could overcome the neuroscience? the buzz. Many were conservatism of traditional peer review. skeptical and predicted it would be a fad, and I Peter Hegemann: We were involved from the of course was both curious and skeptical—but Gyuri Buzsáki: The impact of optogenetics beginning, as we discovered the main player, really too naive to let my skepticism deter my was big and instantaneous. I think all ‘engi- Channelrhodopsin, but we never expected curiosity. Pretty soon, we just tried working with neer types’ immediately recognized that this such an enormous impact. ChR2, trying to replicate the effects seen in the was the method we were all waiting for. My lab Boyden et al. 2005 paper. It was remarkable how was doing closed-loop experiments in the hip- Rob Malenka: I was excited about the pos- well it worked and it was exciting to get spiking pocampus at that time using electrical stimula- sibilities, but was skeptical that optogenetics from patching onto cells, and it quickly became tion and only speculated about the possibility

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of affecting specific neuron types and possibly was more than just the evident usefulness of the et al. Neuron 33, 15–22 (2002)) and demon- single neurons in neuronal circuits. As soon as technology itself. Indeed, in my opinion, it is to strated that genetically targeting the photore- we were able to affect specific neurons optoge- the credit of Deisseroth and Boyden that they ceptor allowed one to netically in my lab, I gave away my two-photon had recognized early that by freely sharing the control specific neu- microscope setup, as identifying and manipulat- reagents and methods they can make optoge- ronal populations. A ing cell types combined with large-scale record- netics as much of a basic necessity in neurosci- paper published in ing of neurons became possible in the freely ence labs as PCs, iPhones and iPads came to be April 2005 showed moving animal. What more can one wish for? in the lives of everyday citizens. This is a part of that optogenetic their genius that made optogenetics spread like activation of different Richard Tsien: I was very excited about the wildfire. The open-source philosophy that they circuits in the brain Gero Miesenböck experimental possibilities it opened up and adopted stands in stark contrast to numerous could change specific proud of the joint accomplishment of two other techniques where the developers tightly aspects of an animal’s behavior (Lima, S.Q. & former graduate students who had worked at control all material and procedural aspects of Miesenböck, G. Cell 121, 141–152 (2005)). different times in my lab at Stanford. their methodology for short-term gain, which These precedents do not diminish the practi- in most, albeit not all, cases has proven to be cal importance of Boyden et al. Swapping ChR2 Ivan Soltesz: I immediately knew that opto- a rather penny-wise, pound-foolish attitude in for the opsin used earlier (because the molecular genetics was going to have an unprecedented the long run. identity of ChR2 was still unknown at the time) impact on neurosci- made optogenetics more effective and much ence because it was a Yukiko Goda: My first encounter with optoge- simpler to use. The alignment of simplicity, ease technology that virtu- netics and a glimpse into the future was hear- of use and efficiency catalyzed the rapid spread ally all neuroscientists ing a talk by Gero of optogenetic technology throughout neuro- had been waiting for, Miesenböck. It was science. Although I knew from the moment I one way or another, so striking to see a had the original idea that optogenetics would be consciously or not. I fly being controlled transformative, the field didn’t explode until the Ivan Soltesz think that many peo- like a mechanical toy currently dominant version of the technology ple had been keenly of sorts simply with was introduced in September 2005. But it also aware of the fundamental veracity of Francis a beam of light. The took a while for the fundamental concept to sink Crick’s major challenge to neuroscience that he Yukiko Goda visual impact was so in. One of the reviewers of the first optogenetics formulated in 1979, that is, that the path for- strong that one could paper (Zemelman, B.V. et al. Neuron 33, 15–22 ward to understanding neuronal circuits and almost intuitively grasp the significance of (2002)) asked whether it wouldn’t be better to the associated behaviors was through the devel- the technology for coming years. This was in study the retina instead, “which conveniently opment of a technology that allows the selective contrast to the knockout mouse technology. has light-sensitive cells already built in.” in vivo control of one type of neuron without Although being of equal or greater importance affecting the activity of all others. Historically, in advancing broad areas of life sciences, includ- Georg Nagel: There are good reasons to there is no doubt that several scientists, myself ing neuroscience, its impact was less immediate argue that optogenetics came onto the scene included, for at least a decade before the pub- and required more academic thoughts. before 2005. Gero Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature lication of the Boyden et al. paper in 2005, had Miesenböck pub- entertained the possibility of making specific Christian Lüscher: I was curious, but it took lished ‘chARGe’ in types of neurons light sensitive and using light us 2 years to get started and try ourselves. The 2002 (Zemelman, npg to switch them on and off. Some tried to make issue for us was the virus that would not express B.V. et al. Neuron it happen and did not really succeed, while oth- well initially. We also played around with dif- 33, 15–22 (2002)), ers did not even try; for example, when I, as a ferent light sources, using expensive lasers, a combination of fresh assistant professor, had raised the possibil- until we realized that many of the cheaper three proteins that Georg Nagel ity of optogenetics to an accomplished senior LEDs had enough power. Once everything was made neurons light scientist at my institution in 1995, he rolled his in place, it took us another 6 months to see the sensitive, and Kramer, Trauner and Isacoff eyes and told me that it would be impossible to first photocurrents… and ever since there was applied a chemical optogenetic approach in express enough of the light-sensitive proteins to no stopping. I certainly did not foresee the full 2004 (Banghart, M. et al. Nat. Neurosci. 7, generate measurable photocurrents, and I had extent of the transformation that optogenetics 1381–1386 (2004)) to silence neurons. Current believed him (entirely my fault, not his). But would bring to neuroscience, but the concept Biology published the first truly non-invasive the point is that optogenetics was ‘in the air’, was so clear that there was no doubt that every- light-manipulation of animals: C. elegans in something that was expected to arrive one day, body would use the technique. 2005 (Nagel, G. et al. Curr. Biol. 15, 2279–2284 and when it finally did, many of us instantly (2005)) and Drosophila in 2006 (Schroll, C. et recognized its importance. However, what I, for Gero Miesenböck: The timeline implied by al. Curr. Biol. 16, 1741–1747 (2006)). one, did not expect was how incredibly fast the your question is incorrect. Optogenetics did But optogenetics is not restricted to neu- basic proof of concept was developed into a ver- not suddenly come “onto the scene 10 years rons, and therefore our demonstration of a satile, easy-to-use, widely accessible technology ago”; on the contrary, all the core concepts of heterologously expressed light-sensitive pro- that it is today. 10 years is an awfully short time, optogenetics were established well before the ton channel in 2002 (Nagel, G. et al. Science and if we use my personal time metric, we could Boyden et al. paper appeared. A paper pub- 296, 2395–2398 (2002)), but even more so the say that it is only 2 NIH grant cycles (a cycle lished in January 2002 showed that light act- strong light-induced depolarization of several defined as a typical 5-year R01 grant). But what ing on an ectopically expressed opsin could animal cells, including human embryonic kid- made the rise of optogenetics so fast? I believe it be used to stimulate neurons (Zemelman, B.V. ney (HEK293) cells, via Channelrhodopsin-2

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in 2003 (Nagel, G. et al. Proc. Natl. Acad. Sci. What types of studies or approaches do or Neurons for hunger and thirst transmit USA 100, 13940–13945 (2003)), was a demon- you think represent the most effective a negative-valence teaching signal from stration of optogenetics. usage of optogenetics in neuroscience the Sternson lab Coming back to the question, I did not believe research? (Betley, J.N. et al. that Channelrhodopsin would have such a Nature 521, 180–185 transformative impact on neuroscience, but I Gero Miesenböck: I feel that optogenetics (2015)). Papers like believed already in 2002 that Channelrhodopsin is used most productively in two situations: these are probing has great power and potential, therefore we when one knows very little about neural mech- and discovering new (Ernst Bamberg, Peter Hegemann, Georg Nagel) anisms and when one knows a lot. In the first circuits and linking applied for a patent in the EU and US before situation, optogenetics can help identify the specific cell popula- Jaideep Bains publication of Channelrhodopsin-1. important players (much like conventional tions to behaviors. It’s forward genetic screens can), and in the sec- important to point out that the papers pushing Roger Tsien: Certainly Francis Crick foresaw ond, it can be used to test hypotheses. the boundaries now don’t rely solely on opto- the transformative impact much earlier, writ- genetics, but use it in combination with che- ing “The tendency in Kay Tye: At this point, optogenetics is just mogenetics and in vivo imaging. Optogenetics neuroscience (and another tool in our arsenals that can be is one (very important) tool in the toolbox for I’m hoping that this applied in conjunction with readouts for dissecting circuit function. will change) is to say, naturally occurring neural dynamics to test ‘Yes, I’d love to have hypotheses about causal relationships. There Has there been a major breakthrough new tools, but will is nothing wrong with using optogenetic in our fundamental understanding of someone else please approaches to validate long-standing hypoth- brain function that could not have been possible without optogenetics? develop them’?”… Roger Tsien eses, although at this point in the field, it is a “One of the next powerful strategy for identifying completely requirements is to be able to turn the firing novel roles for neural circuit constituents. Christof Koch: Not yet. of one or more types of neuron on or off in the alert animal in a rapid manner. The ideal Silvia Arber: I think any study that makes very Michael Häusser: Many important discoveries signal would be light, probably at an infrared careful use of optogenetics and, in particular, have been made using optogenetics, but if one wavelength to allow the light to penetrate far is aware of the fact that optogenetic activation sets the bar high for defining a major break- enough. This seems rather far-fetched but it assesses what a neuron can do, but not what a through, then the answer is “not yet.” That is conceivable that molecular biologists could neuron does do. I often compare optogenetic does not mean that it hasn’t illuminated almost engineer a particular cell type to be sensitive to activation technology to methods removing a every corner of neuroscience and transformed light in this way.” cell at early developmental stages from its con- the way we do experiments. This was published in 1999 (Crick, F. Phil. text in the embryo in order to challenge it to Trans. R. Soc. Lond. B. Biol. Sci. 354, 2021– differentiate into something else in a dish. Also Gina Turrigiano: 2025 (1999)), but he had been saying more or there, such manipulations reveal potential, but I would say that to less the same idea for decades until colleagues not the normal fate of a cell. date the outcomes Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature such as myself persuaded him to make a pub- have been somewhat lishable citation. Jaideep Bains: Visualizing hypothalamic modest. The tech- I wrote to Peter Hegemann an e-mail explic- network dynamics for appetitive and con- nology, combined npg itly linking the involvement of Chlamydomonas summatory behaviors from the Stuber lab with advances in opsins (see Box 1). (Jennings, J.H. et al. Cell 160, 516–527 (2015)) Gina Turrigiano molecular genetics, has allowed circuit- breaking to be done more precisely than previ- BOX 1 ously possible. On the other hand in my view many of the ‘gee wiz’ publications that get the Date: Sun, 10 Oct 1999 22:41:11 -0700 media all hepped up—that is, ‘remote control To: [email protected] this and that’—were pretty obvious from what From: “Roger Y. Tsien” we already knew. Subject: algal rhodopsins

Dear Professor Hegemann: I have been interested for some time in potential methods John Huguenard: by which mammalian neurons might be transfected with a gene whose product would Functional stud- permit light-triggering of depolarizations and action potentials. Eventually I came ies of specific long- across your outstanding pioneering work on the light-activated conductances and opsins range projections of Volvox and Chlamydomonas. However, I cannot find any papers on heterologous were not possible expression of these opsin genes, especially in the systems more commonly used before. Whether the in electrophysiology, such as Xenopus oocytes or HEK293 cells. Has heterologous insights obtained are expression been seriously attempted? If it has, but no light-activated currents were a breakthrough or John Huguenard detectable, is it known whether the problem was in (a) getting enough protein expressed not remains contro- on the plasma membrane, (b) incorporating retinal or (c) finding a partner channel, if versial because there are challenges in relating the opsin itself proved not to be the channel? mouse behavior to humans. Our studies on thalamocortical connectivity in the Gria4-/-

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paper (Paz, J.T. et al. Nat. Neurosci. 14, 1167– One point that is tremendously important, Jaideep Bains: I think we can be more ambi- 1173 (2011)) enabled in a way the study of Bo Li but very difficult to quantify, is the emergence tious with our questions. on selective attention. Driving of parvalbumin of a sort of can-do attitude thanks to the co- cells to produce gamma would not have been development of optogenetics and genetic engi- Patricia Janak: Optogenetics has vastly possible, and although predicted from earlier neering. No problem is too difficult to tackle, increased the precision with which systems theoretical studies, this function, and the ability no mystery too opaque to be penetrated. This neuroscientists can to modulate it by light, is a breakthrough. brave new attitude alone makes optogenetics, make causal connec- along with genetic engineering, an extraordi- tions between a given Sheena Josselyn: At first, the studies using nary game-changer in our field. circuit and a given optogenetics were mostly confirmatory (veri- behavior. It has been fying lots of what we already knew about how Rob Malenka: ‘Fundamental understanding’ a game-changer for the brain worked from decades of lesion/ may be too strong a phrase. Optogenetics has our research. We are pharmacology and genetic studies). I think certainly advanced in the phase where Patricia Janak this is true of most new technologies (such our understanding this precision allows as fMRI). Scientists needed to be convinced of brain function in us to take apart circuits little by little. In the that it works as advertised before they started very important and future, we will need to use optogenetics in new thinking about how to do really interesting even astounding ways, along with other approaches, to then and innovative experiments to take advantage ways. But it has not determine how multiple parts of a circuit work of the power offered by this new tool. I think caused a true para- together in an integrated fashion, in vivo—this the field has now begun to design experiments Rob Malenka digm shift (using will be a fascinating challenge! that take full advantage of this tool. But again, the term correctly as it is only a tool and should not be used to drive Kuhn intended) in how neuroscientists think Richard Tsien: It has greatly heightened our the experimental question. about brain function. We still think about interest in attaching functions to particular cell circuits and how they function. We can just types, and in moving from questions of single Ann Graybiel: The use of optogenetics has explore circuit function and define novel cir- neurons to circuits. It makes it much more allowed for the first time the manipulation of cuits in ways that we could not do and were honorable to be a toolkit inventor, building specific neural cells in fact, unimaginable, without optogenetics. on the precedent of Roger Tsien, Erwin Neher in real time in awake, and Bert Sakmann. behaving animals. How has the advent of optogenetics Prior use of electri- changed the types of scientific Christian Lüscher: Optogenetics is the begin- cal microstimulation questions you ask and your approach to ning of causal neuroscience! For the first time allowed rapid manip- solving them? it has become easier to manipulate the brain ulation, but failed to than to observe its function. I am convinced allow manipulations Ann Graybiel Christof Koch: We can move from observing that if optogenetics is used carefully, it will with cell-type speci- the brain to interfer- help us understand how neurons generate ficity. Because neurons with different func- ing in it. Given the behavior. This, however, will require that we Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature tional characteristics are intermixed side by sheer inexhaustible develop new observation techniques that have side, manipulations without cell-type speci- multiplicity of causal the same spatial and temporal resolution as ficity could not reveal the extent of functional factors responsible optogenetics (for example, imaging activity npg specificity of microcircuits in the mammalian for any one action in of ensembles using genetically encoded cal- brain. The combination, in optogenetics, of the nervous system, cium indicators) such that the manipulations fast kinetics and cell-type specificity has led inferring which ones Christof Koch can be tailored to closely mimic physiological to a major breakthrough in our identification are actually responsi- neural activity. of, and understanding of, this feature of neural ble will not be easy even though we now have circuit design: within any given circuit, there is the technology. Antonello Bonci: extraordinary cell-by-cell microcircuit speci- Before optogenetics, ficity, whereby intermingled neurons with dif- Silvia Arber: Working on questions of motor my laboratory used ferent patterns of connectivity can influence control, the temporal resolution that optoge- electrophysiology in ongoing and future behavior in strikingly netics offers is very combination with selective ways. Such circuit design was, of valuable. It is now molecular and behav- course, posited before, and was familiar espe- possible to study at ioral approaches cially to neuroscientists working on inverte- millisecond resolu- to study drug and Antonello Bonci brates, but before optogenetics, this selectivity tion how changing reward-dependent could rarely be examined systematically at the neuronal activity of synaptic plasticity, but we didn’t have any tools experimental level in mammals. As an exam- defined neuronal to understand which brain pathways were ple, this feature of optogenetics has allowed populations influ- relevant to process/modulate these behav- Silvia Arber neuroscientists to uncover specific functions ences motor behav- iors. When we started using optogenetics, we of interneurons never before open to experi- ior. That allows us to make the link between could finally start addressing which pathways mental analysis. It further has allowed the dis- genetically/developmentally defined neuronal matter and for which behaviors. Furthermore, covery of a level of online control of behavior populations and their precise function in an it allowed my team to address another fun- never before identified by previous methods. animal in vivo. damental question: the relationship between

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synaptic strength and drug-dependent and patch-clamping remains a highly specialized Ivan Soltesz: I think it is definitely comparable. reward-related behaviors. Optogenetics method that can only be used to address a However, in a way, it was more useful because, offered us the opportunity of major leaps for- very circumscribed, finite group of ques- unlike patch-clamp or MRI, optogenetics is a ward in our understanding of these complex tions. Prior to patch clamping, we still had control technology that allows the investigator behaviors. Yet this isn’t the best part about traditional intracellular recording techniques to interfere with and rationally manipulate the optogenetics. Optogenetics allowed my lab that worked for many of the questions that neuronal system in a causal manner in vivo, to attack the most relevant question that has CNS electrophysiologists wanted to address. and not ‘just’ record/describe the activity or haunted me since I became a scientist: how Of course, patch-clamping allowed biophysi- structure. Furthermore, patch-clamping and to translate quickly and effectively our rodent cists to look at single channel properties, but MRI, to remain with these specific examples, studies into treatments for patients. that topic interests a small number of neuro- never really spread beyond the labs that had scientists. In contrast, optogenetics opens up already been doing electrophysiology or imag- Jessica Cardin: The ability to manipulate tar- new types of experiments that a broad array of ing, whereas optogenetics found applications geted cell classes on a fine temporal scale has neuroscientists are interested in ­performing— in virtually all aspects of neuroscience. It is a dramatically changed the way we pose ques- ranging from hardcore cell biologists and very rare technology that can impact so many tions about network interactions. Rather than electrophysiologists to behavioral neurosci- fields so fast and so thoroughly. compiling extensive entists working in species ranging from flies observations and to monkeys. Optogenetics also has a broader Sheena Josselyn: Optogenetics is right up there making inferences impact on basic neuroscientists than MRI with these other transformational technologies. about the impact of a because MRI needs such highly specialized The wonderful thing about optogenetics though particular cell class, and expensive equipment and technically is is that both labs interested in patch-clamp and we tend to ask the only understood by a small group of investi- labs interested in MRI can now incorporate causal questions at gators. Thus, it’s accessible to a small number optogenetics into their arsenal. This technique the beginning of a Jessica Cardin of working neuroscientists. Plus the tempo- is agnostic to the type of question being asked. series of experiments ral and spatial resolution of fMRI approaches It can be used in slices, behaving rodents and and examine both causal and observational really limit what it is able to tell investigators. non-human primates. Plus, the ease with which data in parallel. Rapid iteration of optogenetic optogenetics can be set up and used makes it and viral tools has also led us to make fewer Yukiko Goda: From my perspective, optoge- attractive to non-aficionados. I’m amazed by up-front assumptions about experimental netics thus far have been powerful in charac- how many labs have incorporated optogenetics limitations. terizing brain circuits at the mesoscopic scale. into their research without a huge investment This is somewhere between MRI, which has in training (unlike patch-clamp) or equipment Michael Häusser: been revolutionary in functional mapping of (unlike MRI). The way the optogenetics tools It has completely macroscopic brain regions, and patch-clamp have been shared also makes it easy for new labs changed how we do recording technique, which has had an enor- to use this technique. The brain, for whatever experiments in cel- mous impact on neurophysiology at molecular reason, seems highly forgiving. That is, large lular and systems and cellular levels. Not to mention, though, behavioral effects are observed when largely neuroscience. It has optogenetic tools have also been useful for undefined groups of neurons are synchronously Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature provided us with addressing questions at the cellular level. driven by ChR2. Although the early studies did Michael Häusser powerful tools for not even attempt to recapitulate the precise making causal links Anatol Kreitzer: Optogenetics has been the temporospatial firing properties that the brain npg between elements of neural circuits and most influential breakthrough in neurosci- normally uses to communicate, nonetheless, the behavior—in that we can prove both necessity ence during my scientific career. It is at least as standard 20-Hz stimulation typical of the early (by inactivating neuronal populations) and important as any major technical development experiments produced large, reliable behavioral sufficiency (by activating the same neurons). in the past century, including Golgi staining, responses. It’s as if this manipulation was suf- It is progressively replacing conventional voltage clamp, patch clamp, GFP, calcium indi- ficient to nudge the circuits into a different state. pharmacological experiments, in that now cators and two-photon microscopy. one can directly identify the contribution of Thomas Insel: The importance of optogenetics a particular neurotransmitter pathway, rather Richard Tsien: Interesting that you happen to is that it brings neuroscience closer to causal- than just the involvement of a receptor for a draw comparisons with methods that are largely ity. The first 50 years of neuroscience have been neurotransmitter. And it has meant that we devoted to measuring mostly observational and correlational. Because are progressively abandoning stimulating and activity rather than optogenetics allows us to turn on and turn off recording electrodes, the tools that I grew up merely manipulat- function with cell-specific, millisecond preci- with as an electrophysiologist. ing it. Optogenetics sion, we can begin to identify the activity that is way up there in the is both necessary and sufficient to link neural How does the advent of optogenetics way it has captured function to behavior. There are limits, but this compare to other technological the imagination of is a transformative technology for neuroscience. breakthroughs such as the patch- experts and lay pub- Richard Tsien One other important insight from this technique clamp recording or magnetic resonance lic alike. But I have is that the fundamental advance—using an imaging? to chuckle when newcomers think that practi- opsin—simply borrows from an experiment of cally every problem in neuroscience calls for an nature. Indeed, some of the best science of the Rob Malenka: I think it has had a much big- optogenetic approach. But no question that the last few decades has come from studies in arcane ger impact than patch-clamping because methods are very powerful. species where natural adaptations have revealed

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extraordinary opportunities. Neuroscientists Anatol Kreitzer: Scientific questions should with science. Of course, a tool is never enough, who become naturalists, poking around in the always be primary. If you are following tech- it must be used to build understanding and/or broad world of biology for new tools, almost nological innovation, it’s akin to the ‘streetlight build treatments. always find something interesting. effect’ where you are searching where it’s easi- est (under the streetlight), but not necessar- Rui Costa: Both go Having witnessed the proliferation of ily where it’s most productive (where you lost hand in hand: the optogenetics, should tools be developed your keys). In the case of optogenetics, it has technology is enabling to answer specific scientific questions, enabled a vast number of experiments that are for the prepared or should technological innovation come yielding critical new information about brain mind. If it would have first and the scientific questions follow? function. If it enables you to address long- arrived earlier before standing questions, that’s great. If you want to optics was so easy and Dan Johnston: Technical innovations always use it only because it’s an exciting new tool that Rui Costa before circuit map- lead the scientific questions, and this has cer- everyone is using, that is absurd. ping tools and trans- tainly been true with optogenetics. Given the genesis and genetic tools were less developed, it right tools, clever Gyuri Buzsáki: Carl Ludwig, the inventor of is unclear if it would have taken off so fast. The scientists will always the kymograph, advocated that “Methode is field was ready and in need. come up with novel Alles.” While there is questions that can truth in this wisdom, Sheena Josselyn: Both must be done in con- be answered with the the history of science cert. New tools can inspire research—reminds new techniques. They shows that there is me of Maslow’s ham- might not have even no simple recipe. For mer (that if all you thought of the ques- example, holography have is a hammer Dan Johnston tions without them. and its possible impli- everything starts cations were outlined Gyuri Buzsáki looking like a nail). Christof Koch: Both will happen simultane- early, but practical Tool development ously, one driving the other in a continuous applications had to wait for fast and reliable can allow scientists loop. lasers. On the other hand, single-cell PCR and to ask entirely new Sheena Josselyn GFP-labeling methods fertilized thinking and questions. With the Scott Sternson: Technology, including opto- brought about numerous discoveries not only BRAIN initiative and similar global funding genetics, is developed to address a scientific not possible without them, but which were not mechanisms, the development of tools has need that is relevant to many questions. Before even conceived before the existence of those been garnering a large amount of attention optogenetics, it was clear that approaches to methods. Just as nature exploits whatever sub- (and resources). However, the value of a tool manipulate the activity of specific neuronal strate or mechanism is available for novel solu- only becomes apparent when it is put to use cell types were needed, and there had been tions, the scientific community also quickly in service of an important biological question. various attempts at this before optogenetic jumps on novel methods because they provide Here’s a funny story about the subtle scien- methods were achieved. Channelrhodopsin, new windows on existing ­problems and new tific pressure to adopt the latest tools. A few Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature in particular, turned out to be remarkably easy windows offer new views. Novel techniques years ago, I gave a presentation where I showed to use and was quickly adopted by neuroscien- always undergo an evolution. The initial, hyper- our labs’ data on overexpressing a transcrip- tists working on all types of questions. enthusiastic phase is often mixed with outra- tion factor and examining the effect on npg geous claims about the novel method’s power memory. As soon as I finished, one audience Gero Miesenböck: The scientific question and specificity. In the maturational stage, the member’s hand shot up and the listener que- must always take center stage. I get dismayed claimed super-specificity and super-sensitivity ried the ‘non-physiological’ way in which I had when postdoc applicants want to join my lab issues are reduced and replaced by more sober manipulated the brain. He suggested that we to work on optogenetics, or when search com- understanding of the objective and reliable instead use a more natural approach. Feeling mittees approach me to suggest faculty can- values of the method. In the third phase, the slightly annoyed by this, I concurred that our didates in optogenetics. Imagine 30 years ago innovation is adopted by a large community manipulation was indeed non-­physiological. there had been a hiring spree of faculty work- and combined with other methods. This is What we really needed to do was to artificially ing on PCR. What would these people have typically the stage when major breakthroughs express a protein from a bacteria in neurons been doing since then? are expected. Optogenetics is currently quickly in the brain, implant an optical fiber and then transitioning between the first and third stages, shine a light on these neurons. I asked my Yang Dan: I think but the hard work needed for the maturation inquisitive colleague if this approach would it goes both ways, stage needs to be invested sooner or later as well. be more physiological. He nodded his head in people are motivated agreement. It just goes to show how the field to develop new tech- Krishna Shenoy: Neuroscience tools are has really embraced optogenetics and now niques when they see extremely important, just as in all other areas feels it is a standard (must-use) technique. major technical road of science and engineering. I’m very happy that blocks for a particu- President Obama’s BRAIN initiative has high- Ernst Bamberg: This question is difficult to lar field, but some- Yang Dan lighted the importance of this. And of course answer because, depending on the situation, times a technique optogenetics is a shining (no pun intended) both approaches can be helpful; in other words, finds surprising application in another field example of this. Tools can lead, tools can fol- this is not a clear alternative. I like to cite Max that the developer is not initially aware of. low and tools can be developed hand in hand Planck: “Knowledge precedes application.”

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The optogenetic tool ChR was found exactly these patterns in the exact subset of neurons delivery, binding affinity, etc. Another idea that according to the motto by Max Planck because using optogenetic activation or silencing. Most several groups have initiated effort toward, but we wanted to know how this molecule works, approaches today involve synchronous acti- still requires development, is the use of magne- which afterwards was applied to optogenet- vation or silencing of the neurons. Improved tism to activate genetically encodable proteins ics. Now optogenet- fidelity to the endogenous activity patterns because it could be highly penetrant, non-­ ics opens from its would truly realize the potential for optoge- invasive and could be relatively fast. beginning completely netics to test the causal relationship of neuron new possibilities for activity patterns in the brain to behavior. Peter Hegemann: In reality, light is not a good new scientific ques- medium to activate proteins in large animal tions, which requires Gero Miesenböck: I see three principal limi- ; light is more suitable for transparent for many problems tations. The first is the difficulty of gaining model organisms like C. elegans, Drosophila the development of selective and comprehensive genetic access and Zebrafish. Ernst Bamberg appropriate tools. to the neurons of interest. The second is the What we need for mammalian brains are difficulty of tailoring optical control signals proteins that are sensitive to other media as Richard Tsien: I am troubled by the word to individual cells in a population rather than ultrasound, teraherz ‘should’, used twice in this sentence. If it’s the population as a whole. This is not only a radiation or mag- ‘should’ as in ‘ought to be’, then who gets to technical problem, but also an intellectual one. netic fields that pen- define this imperative? Funding agencies, peer What types of activity pattern should we play etrate the brain much reviewers, individual scientists or perhaps even back to the brain if we had the ability to do so? better than light. the general public? Here, I prefer the possibly This brings me to the third, most fundamen- What we also need is chaotic patterns of an open system, without tal difficulty: the lack of a theoretical under- improved light con- too much top-down direction. Clearly, funding pinning for much of neuroscience. We don’t trol of DNA editing, Peter Hegemann needs to be balanced for tools invented on spec understand most neural systems well enough gene expression and and funding for goal-driven studies that invent to articulate and test clear hypotheses. light-sensitive enzymes, which not elaborated new tools as they go along. Having spoken with well enough yet but bear a tremendous poten- Hodgkin and Huxley, heroes for many of us, Kay Tye: Right now we need to a priori know tial for future applications in the neurosciences after their landmark work on excitability, I feel the genetic features and have a handle for and developmental biology. strongly that there’s a lot of room for those that expressing optogenetic tools in specific neu- invent their own tools for biological studies and ronal populations. What we can’t really do Anatol Kreitzer: One of the biggest technical those that are happy to use the tools of others. yet is target cells based on specific functions. limitations of optogenetics is the current lack Cole invented the voltage clamp, but Hodgkin Although immediate early gene promoters of tools for local control of axons and pre- and Huxley knew much better what to do with have done a lot in this vein, the windows for synaptic terminals. A number of questions in it. Both contributions were essential. tagging are still very imprecise, many orders systems neuroscience necessitate the control of magnitude greater than the functional of specific axonal projections (for example, What do you feel are major conceptual speed of information transfer in a neuron. to Region A, without affecting projections and/or technical limitations in how Furthermore, just to say that a cell was ‘active’ of axon branches from the same neuron to Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature optogenetics is used in the lab today? during a window is not the same as being able Region B). Selective activation of axons in to identify specific patterns of behavior within Region A with channelrhodopsin yields anti- Rob Malenka: For many uses, we’re still lim- a subset of cells and label only those popula- dromic spikes that may propagate to Region B. npg ited by the availability of Cre driver lines or, tions. So right now, we are not able to selec- Selective inhibition of axons in Region A with more generally, the genetic access to many tively manipulate neurons with highly specific current optogenetic tools has been difficult, at important subsets of neurons. We’re also lim- functionality, and we are limited by the existing best. Developing a tool for temporally precise ited by the light-delivery systems, although genetic tools and/or large temporal windows and reversible optical control of neurotrans- engineers are working hard on this and I think of activity. Furthermore, selective playback of mission would be a major advance. it is likely that in a few years injectable LEDs diverse, specific patterns across large popula- or similar light sources that are controlled tions of neurons also represents an ongoing Botond Roska: When remotely will be available. challenge. This has been a problem that can using viruses as deliv- be tackled in relatively small populations of ery tools, there is Scott Sternson: Optogenetics needs to be opsin-expressing neurons with two-photon a variation in the used primarily to assess the functional sig- imaging, but there are limitations in how expression of optoge- nificance of activity many neurons can be controlled in this man- netic tools. This is a patterns measured ner. Finally, the biggest limitation or challenge major limitation since in vivo during behav- with optogenetics is light delivery. Light is great Botond Roska it precludes quantita- ior. Most studies because it is temporally precise and has many tive interpretation of do not do this yet, specific wavelengths, but it does not penetrate results. Simultaneous optical actuation with but, with improved through fatty tissues very well, and has been readout and feedback could solve this problem deep-brain imaging a challenge when translating to larger brains, in the future. capabilities, it will Scott Sternson like primates. Pharmacogenetic approaches become increasingly address this issue, but come with the tradeoff Krishna Shenoy: There is one on my mind common. However, even if the activity pat- of much slower timescales for onset of activa- much these days, and it can be overcome (we terns are known, we can seldom reproduce tion/inhibition, and these are limited by drug are working on it, together with Karl). The

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major theme of understanding populations and with enough accumulation the natural decreasing the possibility for tumor formation. of individual neurons requires, we believe, a cellular machinery is jeopardized and cells As mentioned above, there are ongoing efforts dynamical systems perspective that has as a may become sick. Much effort would need to apply optogenetics in human brain tissue central concept dimensionality of the neural to be invested in developing and testing safer in several labs using ex vivo approaches (that data. For example, if we record from 100 neu- opsin expression strategies, and these strate- is, resected human brain slices, either acute rons, we often find the motor cortices only gies would need to be tested for years or even slices or organotypic slices). There are private appear to use 10–15 dimensions (independent decades since we understand the brain far less companies that try to make the clinical appli- degrees of freedom; see Cunningham, J.P. & than we understand some of our peripheral cation a reality, fueled by venture capital (for Yu, B.M. Nat. Neurosci. 17, 1500–1509 (2014) systems. For example, using optogenetics to example, Circuit Therapeutics). Exactly where for a review). But, while optogenetics provides help blind people see again is in a different cat- (which disease) will be the one where the first cell type–, temporal- and projection pattern– egory because if opsins are presented to the ret- breakthrough will occur in terms of clinical specific activity modulation, you cannot ‘push’ ina, this does not impose an added risk to the applications is hard to predict, but medically neural activity out in certain dimensions. patient since they are already blind. However, intractable focal epilepsies are definite can- You can push activity up/down in groups of if someone has a mental health problem such didates because, unlike in almost any other cells, but these cells may well (and generally as depression, it is quite possible to impose an application involving the human brain, in the do) contribute to multiple dimensions. So we added risk as we could for example also dam- case of the epilepsies the viral vector could be need to be able to more precisely and selec- age circuits important for cognition or sensory injected and optogenetic control attempted in tively manipulate specific neural dimensions processing while trying to treat the depression. the specific brain area containing the seizure in order to mesh with this other major thrust focus, which will be then surgically resected area of systems neuroscience these days. We Botond Roska: I hope so. We are working on in any case as part of traditional ‘therapy’. think the key is, no surprise, patterned optical it. Another area where clinical application may illumination so that you can more selectively take place is pain, where there is usually a influence specific dimensions. Anatol Kreitzer: Yes, I believe so, and we may well-defined area where intervention can be see some early successful applications (for attempted. Obviously, safe long-term light- Patricia Janak: Scientists need to keep in mind example, in the ret- delivery devices will need to be adopted or the caveats that may arise in some experimen- ina) within a decade. developed, and most likely the first applica- tal designs as a result of synchronous optoge- But I suspect it will tions will be targeted at brain regions closest to netic activation of neuronal populations in be longer before it the dura (that is, not located deep in the brain). bulk that does not mimic natural activity of becomes a widely the neurons or projection fibers in question. used tool for treat- Roger Tsien: Once I did not think so, but my Complementary measurements of in vivo neu- ing CNS disease. mind has been changed by the spectacular ral activity are required to fully understand the Anatol Kreitzer There are many fun- progress toward retinal prostheses such as natural behavior of the circuit in question. damental questions from the group of Duebel in Paris. that need to be addressed. Can optogenetic Jaideep Bains: There are two issues that stand proteins be stably expressed and activated in Christian Lüscher: Yes, eventually, but not in out for me. First, in vivo activation with light human brain without inflammation or dis- the next 10 years. There are many obstacles, Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature results in (potentially) non-physiological ruption of cellular processes over decades? such as cell type–specific targeting, stability synchronization of neural population firing. How will optogenetic proteins be targeted of expression, viral long-term toxicity, etc., Second, its use as a tool in brain slice experi- and expressed in specific cells of the human that preclude translation for the moment and npg ments to examine synaptic function is limited brain? How will light be delivered uniformly much development is required to overcome because of widespread expression in membranes over broad areas deep in the human brain? them. I, however, see a window to use optoge- throughout the cell that can result in recruit- netics to develop new deep brain stimulation ment of calcium release from internal stores. Ivan Soltesz: I really think and hope so. There (DBS) protocols. Characterizing pathological is no doubt that optogenetic-based interven- circuit function (with optogenetics) in non- Do you feel that optogenetics will ever tions do work in experimental animals in sev- neurodegenerative behavioral diseases may become a clinical tool for treating human eral models of neurological and psychiatric lead to blueprints of manipulations aiming at disease? disorders, and by ‘work’ I mean they do things restoring normal circuit function, thus revers- that are otherwise not possible (in my field of ing the pathological behavior (with optogenet- Kay Tye: Regarding diseases of the brain, I closed-loop control of intractable epilepsies, ics). If such protocols can then be emulated would never say never, but there are some for example, optogenetics-based intervention with DBS, clinical major challenges that stand in the way. First, can abort a seizure in a way that interferes with trials can be envi- light delivery represents a component that will only a minimal number and specific types of sioned that test for very likely require it to be an invasive strat- cells; only a few years ago, nobody thought safety and efficacy. egy. Optimization could reduce the degree that one can abort seizures after they have In other words, opto- of invasiveness required, but that is one issue. started without shocking the brain with huge genetically inspired Second, opsin expression is another prob- currents). Optogenetics have also been imple- DBS is the ‘hic et lem. Right now, in animal research, the main mented in non-human primates, and there are nunc’ translation of strategy (aside from transgenic animals) is clinical trials with viral vectors, for example, ­optogenetics. Christian Lüscher viral transduction. But viral vectors typically AAVs. In addition, as we understand it today, do not induce very stable expression, as the insertional mutagenesis may be avoided Thomas Insel: Optogenetics was one of the protein continues to accumulate over time using vectors that remain extrachromosomal, formative technologies that led to the c­ urrent

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BRAIN initiative. Looking back on the tools and of course our goal now is to run studies further, these technologies may also open up developed over the past decade, it was clear on larger populations and standardize this the way to use ongoing activity dynamics to that the field was ready for a major leap for- treatment, in order to define how many ses- predict future behaviors and trigger optoge- ward. This is a great example of the ‘then, sions are required to keep patients free from netic interventions to modulate that future now, imagine’ approach to launching scien- use. While this is the first example behavior; for example, in my own field, I tific programs. One slightly simplistic mis- of such an optogenetic-based rTMS study, I expect to have seizure prediction-based (as sion of the BRAIN initiative is to imagine we predict that many more will follow, for other opposed to ‘just’ seizure detection-based) had the tools for human neuroscience that types of and behavioral problems. optogenetic control of intractable epilepsies we have today for mice. In reality, the need within the next 10 years, that is, to use activity to deliver an engineered channel and a light Michael Häusser: Absolutely. The most likely dynamics that predict the future occurrence source will make optogenetics a tough reach early prospect is for restoring vision in the of the epileptic seizure to trigger the optoge- for deep brain stimulation. But an artificial retina, which is, after all, the most accessible netic intervention and prevent it from ever retina, a prosthetic for a cortical pacemaker part of the brain. taking place. Another major breakthrough or another form of chemogenomics (such as can be expected through the development designer receptors) are all worth consider- Where do you see the use of optogenetics of wireless communications and wireless ing for human application. Seeing what this heading in the next 10 years? powering of the electrophysiological and tool has done for studies in mice, optogenet- optogenetic recording and delivery devices ics should persuade clinical neuroscientists to Dan Johnston: I would love to see optogenet- in freely moving animals. There are several ‘think different’. ics extended to other channels, ones that don’t excellent bioengineering labs that are pushing just fire or silence cells, but those that have the envelope on this key technology that will Antonello Bonci: This is the most extraor- more subtle effects. This could be used as a make the need for tethered in vivo recordings dinary part about optogenetics, which I form of light-activated pharmacology. from behaving animals history. The need is consider the best tool that my laboratory clear; for example, in my lab, where we do has to develop treatments for certain human Ernst Bamberg: A growing number of 24/7 video-EEG monitoring and closed-loop diseases such as substance use disorders. I optogenetic tools are available. Not only optogenetics in mice, the tethered nature of personally love its intellectual and technical ­rhodopsin-based tools exist, but also other the recordings is a huge challenge, especially proximity to therapeutic treatments that have light receptors such as light-activated cyclases since the animals are having robust behavioral been employed for many years with limited, are under study. Still, the main problem is seizures, so it would be truly transformative narrow therapeutic indications. I am refer- the precise cell-specific expression in living to have wireless recording and light-powering ring to brain stimulation techniques such as animals. It would be of great interest for cell technology that would negate the need for repetitive Transcranial Magnetic Stimulation biologists if these tools could be expressed long wires and optical cables that can twist (rTMS) and DBS. While the core features of also in cell organelles. In other words, the and break. Of course, the technology has to DBS, rTMS and optogenetics differ substan- major limitation is the lack of appropriate be dependable and affordable for it to have a tially, they share a similar strength: alter- molecular biology. significant impact. ing electrical activity in brain regions and pathways in order to ameliorate behavioral Gyuri Buzsáki: Methods for interacting with Anatol Kreitzer: The future of systems neuro- Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature symptoms. A concrete proof of my enthusi- brain circuits at the single-neuron, single- science is large-scale, non-invasive, all-optical asm comes from a paper that my group pub- spike level are within reach. Only with such control and recording. This will be obtained lished in Nature back in 2013 (Chen, B.T. et al. high temporal and spatial resolution tech- first in zebrafish and C. elegans, but it should npg Nature 496, 359–362 (2013)). In this study, we niques will it become possible to ‘implant’ eventually be possible within regions of the first showed a marked reduction in prefron- physiologically relevant synthetic patterns into mammalian brain as well. It will require new tal cortex excitability in compulsive cocaine- brain circuits and verify hypotheses based on tools and technology (next-generation voltage seeking rats. We then used in vivo optogenetic correlational observations. sensors, wide-field objectives, new imaging prelimbic cortex stimulation and observed modalities), but it will eventually happen. decreases compulsive drug-seeking behav- Ivan Soltesz: I think that a major break- iors. When I started presenting this data, it through that will take place will have to do Michael Häusser: Even though optogenet- immediately caught the attention of clinicians. with a much-increased availability of truly ics has reached the status of a standard tool As early as July 2013, the first treatment- cell type–specific genetic lines and viral vec- in neuroscience, being applied in thousands seeking patients were already volunteering tors for opsin expression for which currently of labs world-wide, its true potential is only to be treated with rTMS stimulation of their there are no good single genetic markers, beginning to be tapped. The ability to perform frontal cortex, and our initial results, while through either intersectional optogenetics or ‘all-optical’ interrogation of neural circuits preliminary (this first study is being submit- some other new ways. Ways to control cells will be truly transformational, allowing us ted as we speak), are remarkably promising. based on their specific developmental origin to perform precisely targeted and calibrated I also find truly extraordinary the fact that, are also going to be increasingly important, interventions in the spatiotemporal dynamics instead of having to wait 15 years to develop and so will the optical control of gene expres- of neural circuits on the scale of natural pat- a drug target, fellow clinicians could get an sion. Coupling of the optogenetic interven- terns of activity, and should help us to crack optogenetic-based experimental treatment to tion to ongoing activity dynamics in vivo the neural code and pinpoint how circuits are patients in a matter of months. Given that we through the use of miniature imaging and altered during disease. have no treatment for cocaine use disorders other recording devices and closed-loop, yet, I find this opportunity truly promising. on-demand systems can also be expected to Botond Roska: (Fortunately) One cannot pre- rTMS has been around for a very long time, have a transformative impact. Taking it a step dict the future.

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Antoine Adamantidis is in the Department of Psychiatry, Douglas Mental Health University Institute, McGill University, Montréal, Canada, and the Department of Neurology, Inselspital University Hospital, University of Bern, Bern, Switzerland. Silvia Arber is at Biozentrum, Department of Cell Biology, University of Basel, Basel, Switzerland, and the Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland. Jaideep S. Bains is in the Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada. Ernst Bamberg is at the Max Planck Institute of Biophysics, Frankfurt am Main, Germany. Antonello Bonci is in the Intramural Research Program, Synaptic Plasticity Section, National Institute on Drug Abuse, Baltimore, Maryland, USA, the Solomon H. Snyder Neuroscience Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA, and in the Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. György Buzsáki is at The Neuroscience Institute, School of Medicine and Center for Neural Science, New York University, New York, New York, USA. Jessica A. Cardin is in the Department of Neurobiology, School of Medicine, New Haven, Connecticut, USA, and at the Kavli Institute of Neuroscience, Yale University, New Haven, Connecticut, USA. Rui M. Costa is at the Champalimaud Neuroscience Programme, Champalimaud Center for the Unknown, Lisbon, Portugal. Yang Dan in in the Division of Neurobiology, Department of Molecular and Cell Biology, Helen Wills Neuroscience Institute, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, California, USA. Yukiko Goda is at the RIKEN Brain Science Institute, Wako-shi, Saitama, Japan. Ann M. Graybiel is at the McGovern Institute for Brain Research and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. Michael Häusser is at the Wolfson Institute for Biomedical Research and Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom. Peter Hegemann is at the Institut für Biologie/Experimentelle Biophysik, Humboldt Universität zu Berlin, Berlin, Germany. John R. Huguenard is in the Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California, USA. Thomas R. Insel is at the National Institute of Mental Health, Bethesda, Maryland, USA. Patricia H. Janak is in the Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, Maryland, USA, and the Department of Neuroscience, Johns Hopkins University, Baltimore, Maryland, USA. Daniel Johnston is in the Department of Neuroscience and Center for Learning and Memory, University of Texas at Austin, Austin, Texas, USA. Sheena A. Josselyn is in the Program in Neurosciences and Mental Health, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada, and the Departments of Psychology and Physiology and Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada. Christof Koch is at the Allen Institute for Brain Science, Seattle, Washington, USA. Anatol C. Kreitzer is at The Gladstone Institutes, San Francisco, California, USA, and the Departments of Neurology and Physiology, University of California, San Francisco, San Francisco, California, USA. Christian Lüscher is in the Department of Basic Neurosciences, University of Geneva, Geneva, Switzerland, and the Service of Neurology, Department of Clinical Neurosciences, University Hospital of Geneva, Geneva, Switzerland. Robert C. Malenka is in the Nancy Pritzker Laboratory, Department of Psychiatry and Behavioral Sciences, School of Medicine, Stanford University, Stanford, California, USA. Gero Miesenböck is at the Centre for Neural Circuits and Behaviour, University of Oxford, Tinsley Building, Mansfield Road, Oxford, UK. Georg Nagel is at the Institute for Molecular Plant Physiology and Biophysics, Biocenter, Julius-Maximilians-University of Würzburg, Würzburg, Germany. Botond Roska is at the Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland. Department of Ophthalmology, University of Basel, Basel, Switzerland. Mark J. Schnitzer is at the James H. Clark Center for Biomedical Engineering and Sciences, Stanford University, Stanford, California, USA, the Howard Hughes Medical Institute, Stanford University, Stanford, California, USA, and the CNC Program, Stanford University, Stanford, California, USA. Krishna V. Shenoy is in the Departments of Electrical Engineering, Bioengineering and Neurobiology, the Neurosciences and Bio-X Programs, the Stanford Neurosciences Institute and the Howard Hughes Medical Institute, Stanford University, Stanford, California, USA. Ivan Soltesz is in the Department of Neurosurgery, Stanford University, Stanford, California, USA. Scott M. Sternson is at the Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, USA. Richard W. Tsien is in the Department of Neuroscience and Physiology, Neuroscience Institute, New York University Langone Medical Center, New York, New York, USA. Roger Y. Tsien is in the Department of Pharmacology, Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, USA. Gina G. Turrigiano is in the Department of Biology and Center for Behavioral Genomics, Brandeis University, Waltham, Massachusetts, USA. Kay M. Tye is at The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. Rachel I. Wilson is in the Department of Neurobiology, Harvard Medical School, Boston, Massachusetts, USA. Nature America, Inc. All rights reserved. America, Inc. © 201 5 Nature npg

1212 VOLUME 18 | NUMBER 9 | SEPTEMBER 2015 NATURE NEUROSCIENCE