A Role for Synaptic Input Distribution in a Dendritic Computation of Motion Direction in the Retina

The starburst amacrine cell in the mouse retina presents an opportunity to examine the precise role of sensory input location on neuronal computations. Using visual receptive field mapping, glutamate uncaging, two-photon Ca2+ imaging, and genetic labeling of putative synapses, we identify a unique arrangement of excitatory inputs and neurotransmitter release sites on starburst amacrine cell dendrites: the excitatory input distribution is skewed away from the release sites. By comparing computational simulations with Ca2+ transients recorded near release sites, we show that this anatomical arrangement of inputs and outputs supports a dendritic mechanism for computing motion direction. Direction-selective Ca2+ transients persist in the presence of a GABA-A receptor antagonist, though the directional tuning is reduced. These results indicate a synergistic interaction between dendritic and circuit mechanisms for generating direction selectivity in the starburst amacrine cell. •In starburst amacrine cells, excitatory inputs are skewed away from release sites•This skewed distribution enhances direction selectivity in a computational model•Direction selectivity of release sites depends on their dendritic locations•The dendritic direction computation is enhanced by GABAergic lateral inhibition Starburst amacrine cells present an opportunity to examine the precise role of sensory input location on dendritic computations. Vlasits et al. find that the excitatory input distribution is skewed away from outputs, which supports a dendritic computation of motion direction.