The most intensively investigated substrate for direction selectivity is the synaptic connection from starburst amacrine cells to ON–OFF direction-selective ganglion cells (ON–OFF DSGCs) in the mouse and rabbit retina. Moreover, the apparent lack of significant direction selectivity recorded from neurons at the level of the lateral geniculate nucleus, which relays signals from retina to cortex, has suggested that this property must be encephalized in primates, arising initially from neural circuits within primary visual cortex 13, 14, 15, 16, 17. One reason for this dichotomy is that, while a significant fraction of retinal ganglion cells in non-primate mammals show direction selectivity 8, 9, this fundamental neural signal has not been observed in the primate retina, despite dedicated effort 10, 11, 12. Thereafter, investigation of the circuit origins and the neural mechanisms for direction selectivity as well as its functional role in motion processing have proceeded on two largely parallel tracks, focusing on diverse motion-processing areas in the primate visual cortex 5 versus the diverse cell types and circuits in the non-primate mammalian retina 6, 7. Similar content being viewed by othersĪbout 60 years ago, neurons in the mammalian nervous system sensitive to the direction of visual motion were described in the primary visual cortex of the cat 1, 2 and in the retina of the rabbit 3, 4. Our findings open a door to investigation of a precortical circuitry that computes motion direction in the primate visual system. Moreover, we discovered that macaque starburst cells possess a strong, non-GABAergic, antagonistic surround mediated by input from excitatory bipolar cells that is critical for the generation of radial motion sensitivity in these cells. This circuitry includes an ON-OFF ganglion cell type, a spiking, ON-OFF polyaxonal amacrine cell and the starburst amacrine cell, all of which show direction selectivity. ![]() Here we combined functional recordings of light-evoked responses and connectomic reconstruction to identify diverse direction-selective cell types in the macaque monkey retina with distinctive physiological properties and synaptic motifs. In primates, by contrast, direction selectivity is a hallmark of motion processing areas in visual cortex, but has not been found in the retina, despite significant effort. In non-primate mammals, directionally selective cell types and circuits are a signature feature of the retina, situated at the earliest stage of the visual process. From mouse to primate, there is a striking discontinuity in our current understanding of the neural coding of motion direction.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |