External and internal inputs affecting plasticity of dendrites and axons of the fly's neurons.

Neurons and glial cells in the fly's visual system exhibit circadian rhythms through changes in shape and size. Moreover, the number of synaptic contacts between these cells changes during the day and night and in the case of one type of synapses, feedback synapses, is maintained under constant conditions indicating an endogenous origin of this rhythm. The structural changes described above, involving the oscillations in the number of synapses and the size of interneurons and glial cells, are examples of plasticity in the central nervous system driven by internal inputs from a circadian clock and by external stimuli such as light. They are also modulated by visual and other sensory stimuli and by motor activity.