Activation zones in cat visual cortex evoked by electrical retina stimulation

• Published in: Graefe's archive for clinical and experimental ophthalmology 2002-11, Vol.240 (11), p.947-954
• Main Authors: SCHANZE, Thomas, WILMS, Marcus, EGER, Marcus, HESSE, Lutz, ECKHORN, Reinhard
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cats; Differential Threshold; Electric Stimulation - methods; Electrodes; Electrophysiology - instrumentation; Equipment Design; Imides; Medical sciences; Ophthalmology; Platinum; Retina - physiology; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Surgery of the eye and orbit; Visual Cortex - physiology
• ISSN: 0721-832X; 1435-702X
• DOI: 10.1007/s00417-002-0577-5

A retina implant for restoring simple basic visual perception in patients who are blind due to photoreceptor loss requires optimisation of stimulation parameters for obtaining high spatio-temporal resolution. We developed effective low-power epi-retinal stimulation and intracortical recording in semichronically prepared cats. Individually driveable fibre electrodes were inserted through a small scleral incision and positioned at the area centralis. Polyimide-platinum film electrodes were inserted via a corneal incision and fixed by instillation of perfluorocarbon liquid on the internal limiting membrane. For electrical stimulation we used short charge-balanced current impulses of 100-400 micro s duration and amplitudes ranging from 1 to 100 micro A. During stimulation we recorded multiple single-cell and population activities from areas 17 and 18. Recordings were stored digitally. Stimulus-response relations including response strength, cortical activation zones, information transmission, and electrical receptive fields were analysed off-line. We found low-threshold activations with fibre electrodes and polyimide-platinum film electrodes in close mechanical contact to the retina. Retinal stimulation with bipolar charge-balanced impulses resulted in cortical activation zones corresponding to 1-5 degrees visual angle at paracentral locations dependent on the eccentricity of the retinal stimulation point. Retino-cortical transinformation analysis revealed 20-30 bits/s per electrode, corresponding to 10-15 four-level pictures/s. Electrical receptive fields had sizes of 1-3 degrees visual angle. Coarse visuomotor coordination and navigation seems possible with retina implants.