Abstract
Retinal ganglion cells (RGCs) encrypt stimulus features of the visual scene in action potentials and convey them toward higher visual centers in the brain. Although there are many visual features to encode, our recent understanding is that the ~46 different functional subtypes of RGCs in the retina share this task. In this scheme, each RGC subtype establishes a separate, parallel signaling route for a specific visual feature (e.g., contrast, the direction of motion, luminosity), through which information is conveyed. The efficiency of encoding depends on several factors, including signal strength, adaptational levels, and the actual efficacy of the underlying retinal microcircuits. Upon collecting inputs across their respective receptive field, RGCs perform further analysis (e.g., summation, subtraction, weighting) before they generate the final output spike train, which itself is characterized by multiple different features, such as the number of spikes, the inter-spike intervals, response delay, and the rundown time (transience) of the response. These specific kinetic features are essential for target postsynaptic neurons in the brain in order to effectively decode and interpret signals, thereby forming visual perception. We review recent knowledge regarding circuit elements of the mammalian retina that participate in shaping RGC response transience for optimal visual signaling.
Highlights
Los Alamos National Laboratory, Computer & Computational Science Division, Los Alamos, NM 87545, USA; Abstract: Retinal ganglion cells (RGCs) encrypt stimulus features of the visual scene in action potentials and convey them toward higher visual centers in the brain
OFF bipolar cell types (BCs) in direct the photoreceptors may perform signal transition sustained that are contact in directwith contact with the photoreceptors maya perform a signal from transition from to transient when they express AMPA receptors, but maintain sustained responses when sustained to transient when they express AMPA receptors, but maintain sustained rethe signal is conveyed through kainate receptors (Figure 3)
Ground squirrel OFF BCs as well, where GluK1 and GluK5 comprised the kainate recepGluK1 was present in Cb1a/b cells, and AMPA receptor subunits were expressed by Cb2 tors of Cb3a/b cells, GluK1 was present in Cb1a/b cells, and AMPA receptor subunits were cells [46]
Summary
The mammalian retina is a valuable and common model in neuroscience, due to its well-defined layered structure and its excellent potential for conducting in vitro electrophysiological studies. GABA as a transmitter and signal the retina is equipped that express inhibitory as a transmitter and laterally, thereby providing feedback and feedforward inhibition to PRs and BCs, respecsignal laterally, thereby providing feedback and feedforward inhibition to PRs and BCs, tively [13] This serves serves mainlymainly as a spatial filter and the basis an respectively [13].inhibition. ACs might provide a sign-inverting feedforward mechanism, such as in the case of S-M (short wavelength–medium wavelength) color opponency in the murine retina, where an S-ON/M-OFF RGC will receive direct excitatory input from S-ON BCs and inhibition through a sign-inverting AC connection from an M-ON BC [20]. There is at least one AC type (VGlut expressing AC) that utilizes a glutamatergic excitatory signaling mechanism to provide a feedforward (ON to ON, OFF to OFF) and crossover (ON to OFF, OFF to ON) glutamatergic input in the case of direction-selective ganglion cells (DSGCs) [21]. Once visual signals have passed through all the above-mentioned circuit elements, they are integrated by RGCs to forge spike trains that inform the brain about the change in only one specific visual aspect [22]
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