Examination of fly motion vision by functional fluorescence techniques

Over the past years, classical electrophysiological approaches to elucidate the functioning of nerve cells have been complemented by functional optical methods, in particular fluorescence imaging. This review illustrates how optical methods have proved helpful in the analysis of the neuronal principles underlying visual motion processing in the fly, a model system which allows physiological investigation under in vivo conditions. Many aspects of dendritic processing in large-field motion-sensitive neurons of Calliphora have been investigated by Ca2+ imaging. In addition, the function of Ca2+ can be addressed directly by manipulating its concentration via UV photolysis of caged Ca2+. The extraction of specific motion information from visual stimuli depends on interactions between individual neurons. A powerful technique to dissect the motion-vision circuit is the photoablation of single neurons. By selective photoablation the role of individual neurons within synaptic networks has been clarified. Further advances in the disclosure of visual motion processing may in the future be achieved by imaging the activity of single neurons during the processing of natural inputs. Moreover, the combination of genetic tools with functional fluorescence approaches will help elucidate the role of classes of neurons in the visual motion pathway of the blowfly's smaller companion, the fruitfly Drosophila.