Fig. 1.

Strengths of the optogenetic approach for investigating neural circuit function. (A) Optogenetic tools permit activity in genetically defined cell types within complex circuits to be modulated by light without affecting nearby cell populations of a different genetic lineage. (B) Delivery of light to axon fibers at the projection targets of a genetically defined neuronal population permits the investigation of synaptic function in an input-specific fashion. (C) The spatiotemporal precision of light allows activity within specific neuronal populations to be driven with physiologically relevant millisecond precision to test the causal role of specific patterns of electrical activity for encoding information or driving a behavioral response. (D) The temporal specificity of optogenetic manipulations also allows for the time-locked activation or inhibition of specific neural pathways in vivo during precise moments of a behavioral sequence or during presentation of specific environmental cues, such as tone-light–conditioned stimuli or delivery of aversive shocks. The colored bar depicts the stages of a hypothetical fear-conditioning experiment, where white is the variable inter-trial interval, yellow is the tone-light–conditioned stimulus presentation, and red represents the shock delivery phase of the experiment.