, 2013, Gong et al., 2013, Jin et al., 2012, Kralj et al., 2012 and Lam et al., 2012). Ideally, improved voltage indicators

should dovetail with concurrent advances in targeting proteins to particular cell types or subcellular compartments and would reveal neuronal spiking with millisecond-scale timing resolution, dendritic voltage dynamics, subthreshold inhibition and excitation, and high-frequency oscillations. The improved voltage indicators may well be genetically encoded, but other approaches from chemistry and nanotechnology should also be considered (Alivisatos et al., 2013, Hall et al., 2012 and Marshall and Schnitzer, 2013). While engineered GFP-based tools have transformed neuroscience by enabling the genetically targeted readout of both static anatomy and dynamical activity, experimental GSK J4 nmr strategies to read-in (control) activity dynamics have typically relied on a different class of engineered proteins

(Fenno et al., 2011). Devising methods for safely and effectively expressing in neurons members of the microbial opsin gene family, which previously had been studied for many S3I-201 order years by physiologists investigating membrane properties of organisms such as algae and archaebacteria (reviewed in Zhang et al., 2011), has opened the door to optical and genetically targetable control of neurons with millisecond resolution within systems as complex as freely behaving mammals. This optogenetic approach, based (as with GFP strategies for imaging) on a single delivered protein component, has likewise benefited enormously from protein over engineering (Deisseroth, 2011). For example, the excitatory

channelrhodopsin tools have been engineered to confer many-orders-of-magnitude-increased light sensitivity to neurons (compared with the original wild-type forms) via mutations that selectively lengthen the intrinsic time constant of deactivation of the channelrhodopsin photocurrent (Berndt et al., 2009, Bamann et al., 2010, Yizhar et al., 2011a, Yizhar et al., 2011b and Mattis et al., 2012). Cells expressing these mutant “step-function” channelrhodopsins become photon integrators, and extraordinarily low-intensity light can be used to increase neural activity in deep-brain genetically targeted cells without penetrating brain tissue with optical hardware (Mattis et al., 2012 and Yizhar et al., 2011b). These engineered step-function tools have now found broad application in modulating complex behaviors within systems ranging from flies to worms to mice (Carter et al., 2012, Haikala et al., 2013, Tanaka et al., 2012, Yizhar et al., 2011b, Bepari et al., 2012 and Schultheis et al., 2011). Other forms of protein engineering have (1) accelerated deactivation of photocurrents for improved temporal precision (Gunaydin et al., 2010 and Berndt et al.