Visual threshold is set by linear and nonlinear mechanisms in the retina that mitigate noise

Abstract

Summary In sensory biology, a major outstanding question is how sensory receptor cells minimize noise while maximizing signal to set the detection threshold. This optimization could be problematic because the origin of both the signals and the limiting noise in most sensory systems is believed to lie in stimulus transduction. Signal processing in receptor cells can improve the signal-to-noise ratio. However, neural circuits can further optimize detection threshold by pooling signals from sensory receptor cells and processing them using a combination of linear and nonlinear filtering mechanisms. In the visual system, the noise limiting light detection has been assumed to arise from stimulus transduction in rod photoreceptors. In this context the evolutionary optimization of the signal-to-noise ratio in the retina has proven critical in allowing visual sensitivity to approach the limits set by the quantal nature of light. Here we discuss how noise in the mammalian retina is mitigated to allow for highly sensitive night vision.

Rhodopsin: A Potential Biomarker for Neurodegenerative Diseases

“…Rhodopsin is synthesized in the rough endoplasmic reticulum of the inner segments of photoreceptors and subsequently undergoes posttranslational modifications in the Golgi before becoming functional (Murray et al, 2009). In Figure 2, an image adapted from an article by Pahlberg and Sampath, 2011 depicts the signaling pathway of rhodopsin. When light activates rhodopsin, phototransduction occurs, initiating the exchange of GDP for GTP on the G-protein, transducing (G t α), consequently increasing cGMP (or cG) hydrolysis through the PDE complex (Pahlberg and Sampath, 2011).…”

Mechanism for Selective Synaptic Wiring of Rod Photoreceptors into the Retinal Circuitry and Its Role in Vision

“…Cones are less sensitive but can respond to a broad range of light intensities of specific wavelengths and thus are essential for daytime and color vision (Kefalov, 2012; Korenbrot, 2012). The functional differences between rod and cone photoresponses are carried downstream through their selective connectivity with distinct classes of bipolar cells (BCs) forming established circuits with known properties that are conserved across vertebrate species (Ghosh et al, 2004; Lamb, 2013; Pahlberg and Sampath, 2011). In the mammalian retina rods establish synapses with a single class of BC, the rod ON-bipolar cell (ON-RBC), forming the highly-sensitive rod bipolar (primary) pathway (Dacheux and Raviola, 1986; DeVries and Baylor, 1993).…”

Ex Vivo Functional Evaluation of Synaptic Transmission from Rods to Rod Bipolar Cells in Mice

“…Patch clamp recordings can be done from rods and rod bipolar cells to measure the photocurrent or photovoltage. Modified from Pahlberg et al, 2011 [3]. Used with permission.…”

“…The activated visual pigment initiates a phototransduction cascade, which reduces the circulating dark-current flowing in through the outer segment, followed by a hyperpolarization of the photoreceptor inner segment membrane potential [1,2]. This change reduces neurotransmitter release to second order neurons, which then allows the neural circuitry of the retina to process and optimize the visual signal transmitted to the brain [3]. Comprehensive evaluation of synaptic transmission from rods to rod bipolar cells (RBC) requires both biochemical and electrophysiological approaches.…”