Editing Motion perception (section)

===Neural mechanism: starburst amacrine cells===
The direction selective (DS) ganglion cells receive inputs from bipolar cells and [[starburst amacrine cell]]s. The DS ganglion cells respond to their preferred direction with a large excitatory postsynaptic potential followed by a small inhibitory response. On the other hand, they respond to their null direction with a simultaneous small excitatory postsynaptic potential and a large inhibitory postsynaptic potential. Starburst amacrine cells have been viewed as a strong candidate for direction selectivity in ganglion cells because they can release both GABA and Ach. Their dendrites branch out radiantly from a soma, and there is a significant dendritic overlap. Optical measurements of Ca<sup>2+</sup> concentration showed that they respond strongly to the centrifugal motion (the outward motion from the soma to the dendrites), while they don't respond well to the centripetal motion (the inward motion from the dendritic tips to the soma).
When the starburst cells were ablated with toxins, direction selectivity was eliminated. Moreover, their release of neurotransmitters itself, specifically calcium ions, reflect direction selectivity, which may be presumably attributed to the synaptic pattern. The branching pattern is organized such that certain presynaptic input will have more influence on a given dendrite than others, creating a polarity in excitation and inhibition. Further evidence suggests that starburst cells release inhibitory neurotransmitters, GABA onto each other in a delayed and prolonged manner. This accounts for the temporal property of inhibition.<ref name=boreul/>

In addition to spatial offset due to GABAergic synapses, the important role of chloride transporters has started to be discussed. The popular hypothesis is that starburst amacrine cells differentially express chloride transporters along the dendrites. Given this assumption, some areas along the dendrite will have a positive chloride-ion equilibrium potential relative to the resting potential while others have a negative equilibrium potential. This means that GABA at one area will be depolarizing and at another area hyperpolarizing, accounting for the spatial offset present between excitation and inhibition.<ref>{{cite journal | vauthors = Demb JB | title = Cellular mechanisms for direction selectivity in the retina | journal = Neuron | volume = 55 | issue = 2 | pages = 179–86 | date = July 2007 | pmid = 17640521 | doi = 10.1016/j.neuron.2007.07.001 | s2cid = 5691739 | doi-access = free }}</ref>

Recent research (published March 2011) relying on [[Serial block-face scanning electron microscopy|serial block-face electron microscopy]] (SBEM) has led to identification of the circuitry that influences directional selectivity. This new technique provides detailed images of calcium flow and anatomy of dendrites of both [[starburst amacrine cell|starburst amacrine]] (SAC) and DS ganglion cells. By comparing the preferred directions of ganglion cells with their synapses on SAC's, Briggman et al. provide evidence for a mechanism primarily based on inhibitory signals from SAC's<ref>{{cite journal | vauthors = Briggman KL, Helmstaedter M, Denk W | title = Wiring specificity in the direction-selectivity circuit of the retina | journal = Nature | volume = 471 | issue = 7337 | pages = 183–8 | date = March 2011 | pmid = 21390125 | doi = 10.1038/nature09818 | s2cid = 4425160 | bibcode = 2011Natur.471..183B }}</ref> based on an oversampled serial block-face scanning electron microscopy study of one sampled retina,  that retinal ganglion cells may receive asymmetrical inhibitory inputs directly from starburst amacrine cells, and therefore computation of directional selectivity also occurs postsynaptically.  Such postsynaptic models are unparsimonious, and so if  any given starburst amacrine cells conveys motion information to retinal ganglion cells then any computing of 'local' direction selectivity postsynaptically by retinal ganglion cells  is  redundant and dysfunctional. An [[acetylcholine]] (ACh) transmission model of directionally selective starburst amacrine cells provides a robust topological underpinning of a motion sensing in the retina.<ref>{{cite journal | vauthors = Poznanski RR | title = Cellular inhibitory behavior underlying the formation of retinal direction selectivity in the starburst network | journal = Journal of Integrative Neuroscience | volume = 9 | issue = 3 | pages = 299–335 | date = September 2010 | pmid = 21064220 | doi = 10.1142/s0219635210002457 }}</ref>