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M. E. Ivanova, B. K. Baziyan, S. A. Gordeev; Parameters of Stimulation With Visual Cortical Prosthesis in Behavioral Feline Model. Invest. Ophthalmol. Vis. Sci. 2010;51(13):422.
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© ARVO (1962-2015); The Authors (2016-present)
To determine parameters for visual cortex stimulation evoking phosphene perception in feline behavioral model.
13 felines were tested for their ability to develop conditional food-obtaining reflex in response to "phosphene model". 11 of the 13 tested animals qualified for the experiment and were implanted with either subdural/intracortical iridium-oxide microelectrode array or a single aureated silver electrode, in V1 primary visual cortex. Animals were divided into 4 groups based on the localization of the implant and the diameter of the electrodes (0.05, 0.2, or 1.0 mm). Implantations were controlled using stereotaxic atlas and visual evoked potentials. At the end of surgeries, cranium bones were sealed with acryl oxide adhesive. Follow-up period was 8-12 months. Three categories of parameters affecting phosphene perception were measured: 1) brain-computer interface parameters: position of microelectrode tip, diameter of electrodes, and number of stimulated electrodes (1-8); 2) major phosphene-evoking parameters: current strength, pulse duration and impedance for stimulated electrodes; 3) variables: frequency of stimulation, impulse polarity, and duration of train impulses.
Preferable position of microelectrode tip was in 3rd-4th intracortical layers. Less current strength was needed with decrease in electrode diameter. Phosphene perception appeared when 3 or more electrodes were stimulated. Preferable frequency of stimulation was 25-100 Hz with bipolar -/+ impulses, at train duration of 1-2 s. Pulse duration was 0.3-1.0 ms for subdural and 0.1-0.5 for intracortical prostheses. Optimal intracortical current strength was 0.1-0.4 mA for 0.2-mm electrodes, and 0.02-0.1 mA for 0.05-mm electrodes. Subdural current strength was 1-4 mA for 1.0 mm electrodes, and 0.8-1.5 mA for 0.05-mm electrodes. Impedance for 0.05-mm electrodes achieved 50 kOm in 8 months after implantation, increasing a risk of neural cell damage.
The obtained parameters allow for a long-term (up to 1 year) implantation of visual cortical prosthesis in felines. Further experiments are needed to evaluate longevity and longer-term biocompatibility of microelectrode arrays.
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