Optical Control of Neuronal Activity

Abstract Optogenetics has become an invaluable method to establish causal relationships between the activity of genetically defined neuronal circuits and behaviour. Channelrhodopsin 2 is a light‐activated channel that, when introduced in neurons allows temporally precise control of the activity of genetically identified neuronal networks. Conversely, halorhodopsins are light sensitive ion pumps that allow us to reversibly inhibit neuronal transmission with single action potential resolution. These optical tools offer new approaches to deconstruct neuronal circuits in freely moving animals. New variants of light‐activated channels and pumps offer a menu of optogenetic tools that allow us to determine functional connectivities and dynamic properties of brain networks. The development of optogenetics has profound implications in our understanding of brain organisation and mechanisms of neuropsychiatric disease. Key Concepts: Introduction of Channelrhodopsin 2 in neurons allows millisecond optical control of genetically identified neurons. Different mutants of ChR2 show different kinetic properties, spectral sensitivity. Different gene delivery methods allow dissection of neuronal circuits even in the absence of genetic markers and in multiple model organisms. Combination of optogenetics with gene deficiencies and imaging systems will allow significant improvements in our understanding of circuit dynamics and mechanisms of disease.