Figure 6. Model of parallel pathways.

Light serves at least two functions in the visual system of Drosophila, it entrains and keeps the autonomous circadian clock of photoreceptors in phase and it triggers the phototransduction cascade. Both cellular mechanisms are active in parallel in photoreceptor cells and both converge in the volume control of their synaptic terminals in the lamina. The neuronal readout of this peripherally controlled morphological and functional plasticity is further computed downstream of the photoreceptor terminals, within the lamina and/or e.g. in the lobula plate, to instruct the appropriate behavior.