Activation zones in cat visual cortex evoked by electrical retina stimulation.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
Coarse visuomotor coordination and navigation seems possible with retina implants.
Schanze
Thomas
T
Applied Physics--NeuroPhysics Group, Department of Physics, Philipps University Marburg, Renthof 7, 35032 Marburg, Germany. th.schanze@physik.uni-marburg.de
Wilms
Marcus
M
Eger
Marcus
M
Hesse
Lutz
L
Eckhorn
Reinhard
R
D000818:Animals; D002415:Cats; D004056:Differential Threshold; D004558:Electric Stimulation / Q000379:methods; D004566:Electrodes; D004594:Electrophysiology / Q000295:instrumentation; D004867:Equipment Design; D007094:Imides; D010984:Platinum; D012160:Retina / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*
D007094:Imides; D010984:Platinum