Biosystems. 2005 Jan-Mar;79(1-3):133-42. 

Retino-cortical information transmission achievable with a retina implant.

Eger M, Wilms M, Eckhorn R, Schanze T, Hesse L.

Department of Physics, Neurophysics Group, Germany.

Blind subjects with photoreceptor degeneration perceive phosphenes when their 
intact retinal ganglion cells are stimulated electrically. Is this approach 
suitable for transmitting enough information to the visual cortex for partially 
restoring vision? We stimulated the retina of anesthetized cats electrically 
and visually while recording the responses in the visual cortex. Transmission 
of retino-cortical information T was quantified by information theory. 
T was 20-160 bit/s (per stimulation and recording site) with random electrical 
or visual impulse stimulation at rates between 20 and 40 s-1. While increasing 
spatial density of independent electrical stimulation channels T did not saturate 
with 7 electrodes/mm2 retina. With seven electrodes up to 500 bit/s was transmitted 
to 15 cortical recording sites. Electrical stimulation basically employs temporal 
stimulus patterns. They are intimately linked with intensity/contrast information 
coded by the spike density of retinal ganglion cells. From the cortical information 
spread we estimated the spatial resolution as 0.5mm cortex corresponding to 
0.5-1.0 degrees visual angle. If the human cortex can receive and decode the 
information transmitted by a retina implant, our quantitative results measured in 
cats suggest that visuo-motor coordination and object recognition in many in- and 
out-door situations will be possible.