Optical imaging of the visual cortex in the cat demonstrating local cortical activation after epiretinal stimulation with a completely implanted wireless epiretinal prosthesis

Abstract

Abstract: : Purpose: To evaluate cortical activation after implantation of an epiretinal prosthesis with wireless data and energy transfer. Methods: After implantation of an epiretinal device for retinal stimulation in the anaesthetized cat the function of the device was tested by recording of stimulus artefacts from episcleral electrodes. Optical imaging of intrinsic signals was performed after craniotomy of the contralateral hemisphere. Activity images were collected with a CCD camera focussed 750 µm below the pial surface. For control, monocular (non–operated eye) visual stimuli composed of full field luminance gratings of 4 orientations were used that resulted in characteristic activity patterns, called single–orientation maps, in the visual cortex. In the test protocol, the activity pattern of the cortex was recorded before, during and after activation of the retinal implant without visual stimulation (both eyes occluded). In each protocol, video frames were collected for 4.5 s commencing 1 s after stimulus onset (visual or implant–induced). Results: In all experiments activation of the implant showed episcleral artefacts indicating that the implant was functioning after the surgical procedure. Retinotopic cortical activation was demonstrated according to the area of retinal stimulation. Activation of neighbouring electrode pairs caused a predictable positional shift of the activated cortical zone. Conclusions: Specific and local cortical activation could be achieved with a completely implanted epiretinal prosthesis in the cat. The inductive data and energy transfer was functioning throughout the experiment.

Keywords: retina • visual cortex • imaging/image analysis: non–clinical