Integrated Calendar

The detection of visual motion is a fundamental neuronal computation that serves many critical behavioral roles, such as encoding of self-motion or figure-ground discrimination. For a neuron to extract directionally selective (DS) motion information from inputs that are not motion selective it is essential to integrate across multiple spatially distinct inputs. This integration step has been studied for decades in both vertebrate and invertebrate visual systems and given rise to several competing computational models. Recent studies in Drosophila have identified the 4th-order neurons, T4 and T5, as the first neurons to show directional selectivity. Due to the small size of these neurons, recordings have been restricted to the use of calcium imaging, limiting timescale and direct measurement of inhibition. These limitations may prevent a clear demonstration of the neuronal computation underlying DS, since it may depend on millisecond-timescale interactions and the integration of excitatory and inhibitory signals. In this study, we use whole cell in-vivo recordings and customized visual stimuli to examine the emergence of DS in T4 cells. We record responses both to a moving bar stimulus and to its components: single position bar flashes. Our results show that T4 cells receive both excitatory and inhibitory inputs, as predicted by a classic circuit model for motion detection. Furthermore, we show that by implementing a passive compartment model of a T4 cell, we can account not only for the DS response of the cell, but also for its dynamics.

Vision is inarguably the most dependable of the five senses. The retina contains light sensing protein receptors (rhodopsins) that incorporate a small polyene molecule derivative of vitamin A, known as 11-cis-retinal. Major clues on understanding the visual cycle have been established through the design of variations of the vitamin A light absorbing molecule, some of which will be presented. A detailed understanding of the inner workings of rhodopsin is not only critical from the stand point of solving mysteries of visual diseases, like Age-related Macular Degeneration (the leading cause of blindness), but also serves as a well established model for elucidating the mechanism of other G-protein coupled receptors (GPCRs). Furthermore, we show that the value of light absorbing molecules expands beyond vision and can be used to trigger neurons thereby aiding the delineation of complex neural networks.