High-resolution VSDI retinotopic mapping via a DLP-based projection system

Abstract

High-resolution recording of visual cortex activity is an important tool for vision research. Using a customized digital mirror device (DMD)-based system equipped with retinal imaging, we projected visual stimuli directly on the rat retina and recorded cortical responses by voltage-sensitive dye imaging. We obtained robust cortical responses and generated high-resolution retinotopic maps at an unprecedented retinal resolution of 4.6 degrees in the field of view, while further distinguishing between normal and pathological retinal areas. This system is a useful tool for studying the cortical response to localized retinal stimulation and may shed light on various cortical plasticity processes.

Evaluation and Optimization of Methods for Generating High-Resolution Retinotopic Maps Using Visual Cortex Voltage-Sensitive Dye Imaging

“…We generated the simulated data of an ideal retinotopic mapping experiment, where visual stimuli are presented at different times and at different locations of the retina while the cortical responses are recorded. Accordingly, simulated cortical responses similar to experimental VSDI cortical responses ( Gross et al, 2019 ) were generated at different cortical locations ( Figure 1A ). The simulated responses were generated at a rate of 0.5 Hz for a 10-s “experiment”, to represent the expected responses in our experimental setting, peaking every 2 s (at 1, 3, 5, 7, and 9 s) ( Figure 1B ), corresponding to the stimulus that elicited them.…”

“…All surgical procedures and dye staining were performed as described previously ( Gross et al, 2019 ). Briefly, following anesthesia, the head was fixed using a custom-made steel chamber, attached to the skull above the right primary visual cortex (V1).…”

“…Visual stimuli were projected using a costume-built projection system as previously described ( Gross et al, 2019 ). The system consists of a Digital Light Processor (DLP) Digital Micrometer Device (DMD) projector (DLP LightCrafter 4500, Texas Instruments, Inc., Dallas, TX, United States) controlled by software and passive optical elements that project an image onto the retina of the rat.…”

“…To project the stimulus on the retina, the pupil was dilated through topical application of Mydramide (Tropicamide 0.5%, Fisher Pharmaceutical, Ltd.) and Efrin-10 drops (Phenylephrine HCL 10%, Fisher Pharmaceutical, Ltd.), after which a microscope cover glass ( d = 13 mm) was mounted on the cornea, coupled by an ophthalmic gel, similar to previous publications ( Mandel et al, 2013 ; Gross et al, 2019 ). Real-time imaging of the retinal stimulus was performed by a camera (DMK 33GP1300, The Imaging Source, Bremen, Germany), enabling the localization and focusing of the stimulus on the retina at a desired location with high precision throughout the experiment.…”

“…Electrophysiological studies have revealed that in mammals the localized stimulation of a specific retinal region (corresponding to specific locations in the field of view) induces a localized response in V1 and that there is an orderly representation of the visual field of view in the V1, the so-called retinotopic mapping ( Hubel and Wiesel, 1959 ). Generation of retinotopic maps is of great interest for studying retinal-visual cortex processing, plasticity, circuitry, and for better understanding various pathologies ( Hubel and Wiesel, 1959 ; Gross et al, 2019 ). The typical response in the visual cortex to localized retinal stimuli is activity that starts spatially at the retinotopic site of the visual stimulus ( Bringuier et al, 1999 ; Roland et al, 2006 ; Gao et al, 2012 ) and then spreads over several square millimeters ( Hubel and Wiesel, 1959 ; Grinvald et al, 1994 ; Michel et al, 2018 ).…”