Abstract
The fruit fly Drosophila Melanogaster is the foremost genetic model organism for neuroscientific research and is used to study both basic neuroscience and human genetic neurological disease. In humans, the visual system has traditionally provided a valuable window into both normal and abnormal neural function and non-invasive electrophysiological methods for assaying human visual function are well established. A comparable assay of fly visual function is desirable so that we can compare the effects of disease genes and drug therapies across the two organisms. Here, we have translated a rapid, non-invasive measurement technique (the steady state visually evoked potential - SSVEP) to Drosophila. We report on its ability to rapidly monitor the development of spatial and temporal resolution in different genetic backgrounds. The Drosophila SSVEP exhibits a temporally bandpass response peaking at around 4–8 Hz with the maxima being relatively independent of spatial frequency. Responses to spatial grating patterns peak at around 0.25 cycles/degree but fall off slowly - they are still above noise at 2 cycles/degree. This is well above the spatial resolution limit imposed by the sampling resolution of the Drosophila compound eye. The ability of flies to respond to patterns above the sampling limit is attributed to aliasing and is commonly considered to be a flaw that could, potentially, lead to incorrect flight dynamics and turning behavior. We hypothesized that such aliased information may, in fact, be useful when its spatial envelope defines an object or pattern boundary. In support of this hypothesis, we present SSVEP data showing responses to the temporal modulation of second-order patterns with carriers well above the Drosophila Nyquist limit.