Computation of motion direction in the vertebrate retina

Abstract

How direction of image motion is detected as early as at the level of the vertebrate eye has been intensively studied in retina research. Although the first direction-selective (DS) ret­inal ganglion cells were already described in the 1960s and have since then been in the fo­cus of many studies, scientists are still puz­zled by the intricacy of the neuronal circuits and computational mechanisms underlying retinal direction selectivity. The fact that the retina can be easily isolated and studied in a Petri dish-by presenting light stimuli while recording from the various cell types in the retinal circuits-in combination with the ex­tensive anatomical, molecular and physiolog­ical knowledge about this part of the brain presents a unique opportunity for studying this intriguing visual circuit in detail. This ar­ticle provides a brief overview of the histo­ry of research on retinal direction selectivi­ty, but then focuses on the past decade and the progress achieved, in particular driven by methodological advances in optical record­ing techniques, molecular genetics approach­es and large-scale ultrastructural reconstruc­tions. As it turns out, retinal direction selec­tivity is a complex, multi-tiered computation, involving dendrite-intrinsic mechanisms as well as several types of network interactions on the basis of highly selective, likely genet­ically predetermined synaptic connectivi­ty. Moreover, DS ganglion cell types appear to be more diverse than previously thought, differing not only in their preferred direction and response polarity, but also in physiology, DS mechanism, dendritic morphology and, importantly, the target area of their projec­tions in the brain.

Fly motion vision: from optic flow to visual course control

“…2c). This is analogous to the vertebrate retina where cone photoreceptors contact ON and OFF bipolar cells in parallel (see [23]). However, in the vertebrate retina the split is implemented by different types of glutamate receptors in ON and OFF bipolar cells so that light depolarizes ON bipolar cells and hyperpolarizes OFF bipolar cells, whereas in the fly the dendritic membrane response to light is identical in L1 and L2 and consists of a transient hyperpolarization at the beginning and a rebound excitation at the end of a light pulse.…”