Optogenetics: Illuminating neuronal circuits of memory formation.

Optogenetics has revolutionized the field of neuroscience. Within the last decades the development and use of optogenetics gained enormous importance for the identification of functional synaptic connections. Employing optogenetic tools in anatomically defined pathways offers a straightforward strategy to demonstrate neuronal sufficiency, even during state-dependent activity within a neuronal network. Hunger, thirst, fatigue or motivation each impact an animal's behavior and determine the internal states that tune neuronal pathways to generate context-appropriate actions. In particular, higher order brain processes, such as learning and memory formation, are often state-dependent and here optogenetics can provide the means to identify and investigate the neuronal pathways involved. Our aim with this article is to focus on the possibilities and limitations of optogenetic tools for dissecting the neuronal circuits underlying learning and memory formation in Drosophila, while emphasizing what these approaches can tell us about neuronal circuit function in general.