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Tamar Arens-Arad, Nairouz Farah, Yossi Mandel; Head-Mounted Projection system for visual stimulation and cortical recordings as a novel method for studyng natural and artificial vision in behaving animals. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2231. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Accurately assessing natural and artificial visual function performance in awake and behaving animals is of great importance for studying various retinal diseases and treatments. Here we present the development of a novel customized head-mounted projection system integrated with electrodes for recording visual evoked potentials (VEP) in response to natural and artificial stimulus for assessing visual functions in awake and behaving animals.
We devised and customized a Digital Mirror Device (DMD) based head-mounted system, to project high quality images at visible and near IR light onto the rat retina and performed computer simulations to characterize and optimize the optical properties of the system. The design included a periscope like system to relay the DMD projected image onto the rat retina, and fitted onto the rat skull using a customized head plate and adaptor.VEPs were recorded using electrodes implanted into the visual cortex and embedded into the mounting head plate. VEPs induced by flashes with varying pulse durations (ranging from 0.25msec to 8msec), varying frequency (ranging from 1Hz to 32Hz) and varying contrast levels projected by the head mounted projector were investigated in both anesthetized and awake animals
The system enabled the projection of images with MTF values higher than 0.85, with optimal image quality obtained at a 1mm pupil diameter, with a retinal image diameter of 3mm corresponding to 45 degrees visual field in the rat. Robust VEP signals were recorded in response to images projected at various contrast and light intensity. The VEP amplitude decreased as a function of temporal frequency reaching the noise limit for frequencies higher than 32Hz and increased as a function of stimuli duration, reaching a plateau at pulses longer than 10ms. Similarly, a decrease in VEP amplitude for decreasing contrast was also observed, reaching the noise level at 6% contrast
Our results demonstrate the feasibility of investigating visual function performance in rats using a novel head-mounted projection system. This system may prove to be a vital tool in studying natural and artificial vision in awake and behaving animals, and for the evaluation of various treatments or other interventions, such as training for the studying of visual cortex plasticity.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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