The neuroarchitecture of the circadian clock in the brain of Drosophila melanogaster

Neuroethologists try to assign behavioral functions to certain brain centers, if possible down to individual neurons and to the expression of specific genes. This approach has been successfully applied for the control of circadian rhythmic behavior in the fruit fly Drosophila melanogaster. Several so-called "clock genes" are expressed in specific neurons in the lateral and dorsal brain where they generate cell-autonomous molecular circadian oscillations. These clusters are connected with each other and contribute differentially to the control of behavioral rhythmicity. This report reviews the latest work on characterizing individual circadian pacemaker neurons in the fruit fly's brain that control activity and pupal eclosion, leading to the questions by which neuronal pathways they are synchronized to the external light-dark cycle, and how they impose periodicity on behavior.