Published: June 23rd, 2023
Here, we describe a standard protocol for quantifying the optokinetic reflex. It combines virtual drum stimulation and video-oculography, and thus allows precise evaluation of the feature selectivity of the behavior and its adaptive plasticity.
The optokinetic reflex (OKR) is an essential innate eye movement that is triggered by the global motion of the visual environment and serves to stabilize retinal images. Due to its importance and robustness, the OKR has been used to study visual-motor learning and to evaluate the visual functions of mice with different genetic backgrounds, ages, and drug treatments. Here, we introduce a procedure for evaluating OKR responses of head-fixed mice with high accuracy. Head fixation can rule out the contribution of vestibular stimulation on eye movements, making it possible to measure eye movements triggered only by visual motion. The OKR is elicited by a virtual drum system, in which a vertical grating presented on three computer monitors drifts horizontally in an oscillatory manner or unidirectionally at a constant velocity. With this virtual reality system, we can systematically change visual parameters like spatial frequency, temporal/oscillation frequency, contrast, luminance, and the direction of gratings, and quantify tuning curves of visual feature selectivity. High-speed infrared video-oculography ensures accurate measurement of the trajectory of eye movements. The eyes of individual mice are calibrated to provide opportunities to compare the OKRs between animals of different ages, genders, and genetic backgrounds. The quantitative power of this technique allows it to detect changes in the OKR when this behavior plastically adapts due to aging, sensory experience, or motor learning; thus, it makes this technique a valuable addition to the repertoire of tools used to investigate the plasticity of ocular behaviors.
In response to visual stimuli in the environment, our eyes move to shift our gaze, stabilize retinal images, track moving targets, or align the foveae of two eyes with targets located at different distances from the observer, which are vital to proper vision1,2. Oculomotor behaviors have been widely used as attractive models of sensorimotor integration to understand the neural circuits in health and disease, at least partly because of the simplicity of the oculomotor system3. Controlled by three pairs of extraocular muscles, the eye rotates in the socket primarily around three correspon....
All experimental procedures performed in this study were approved by the Biological Sciences Local Animal Care Committee, in accordance with guidelines established by the University of Toronto Animal Care Committee and the Canadian Council on Animal Care.
1. Implantation of a head bar on top of the skull
NOTE: To avoid the contribution of VOR behavior to the eye movements, the head of the mouse is immobilized during the OKR test. Therefore, a head bar.......
With the procedure detailed above, we evaluated the dependence of the OKR on several visual features. The example traces shown here were derived using the analysis codes provided in Supplementary Coding File 1, and the example traces raw file can be found in Supplementary Coding File 2. When the drum grating drifted in a sinusoidal trajectory (0.4 Hz), the animal's eye automatically followed the movement of the grating in a similar oscillatory manner (Figure 3B
The method of the OKR behavioral assay presented here provides several advantages. First, computer-generated visual stimulation solves the intrinsic issues of physical drums. Dealing with the issue that physical drums do not support the systematic examination of spatial frequency, direction, or contrast tuning8, the virtual drum allows these visual parameters to be changed on a trial-by-trial basis, thus facilitating a systematic and quantitative analysis of the feature selectivity of the OKR beha.......
We are thankful to Yingtian He for sharing data of direction tuning. This work was supported by grants from the Canadian Foundation of Innovation and Ontario Research Fund (CFI/ORF project no. 37597), NSERC (RGPIN-2019-06479), CIHR (Project Grant 437007), and Connaught New Researcher Awards.....
|2D translational stage
|For fixing headplate on skull and protecting skull
|Bupivacaine Injection BP 0.5%. Local anesthesia
|For maintaining moisture of eyes
|Geforce GTX 1650 or Quadro P620.
|For generating single screen among three monitors
|For maintaining body temperature
|High-speed infrared (IR) camera
|For recording eye rotation
|For CR reference and the illumination of the eye
|For reflecting image of eye
|Water and energy supply
|Lidocaine and epinephrine mix
|XYLOCAINE. Local anesthesia
|for calibration of monitors
|analysis of eye movements
|World Precision Instruments
|For scraping skull and removing fascia
|Microscope calibration slide
|to measure the magnification of video-oculography
|Neutral density filter
|to generate scotopic visual stimulation
|Nigh vision goggle
|for scotopic OKR
|to synchronize visual stimulation and video-oculography
|open source software
|visual stimulation toolkit
|For skin removal
|Type: All purpose. For adhering headplate on the skull
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