| ON THE CORTICAL REPRESENTATION OF RETINA IMPLANT
GENERATED FORM AND MOTION STIMULI
|1. Physics Grp Neurophysics, Philipps Univ,
|2. Ophthalmology, Philipps Univ, Marburg, Germany
| A retina implant for restoring visual perception
in patients that are blind due to photoreceptor loss should not only evoke
phosphenes but should also generate cortical representations of form and motion.
Method: In anaesthetised cats we inserted fibre electrodes
through a small scleral incision onto the retinal surface for stimulation.
Alternatively, we implanted foil electrodes. Cortical activities were recorded
in A17/18. Retinal and cortical electrodes were adjusted to corresponding
sites. For electrical stimulation we used charge balanced impulses (50-1000
µs, 1-500 µA). Basic form stimuli of various sizes and shapes
were generated by a selective and synchronous activation of retinal electrodes.
Movement stimuli were produced by translating the form stimuli to different
retinal positions. From cortical recordings we computed stimulus related
spatio-temporal activation profiles for the estimation of the relations between
stimulation distance and form resolution and between stimulus velocity and
Results: Electrical retina stimulation yielded a
spatial resolution of 1-5visual angle
and a temporal resolution of about 20 ms. While spatial resolution depended
on the stimulation current (the higher the current the broader the cortical
activation) temporal resolution was correlated to the stimulation rate. We
found that the measured spatio-temporal cortical activation profiles are commonly
related to retinal form and motion stimuli.
Conclusions: Our results indicate that retina implant
generated form and motion stimuli can be represented by cortical activities.
Supported by: BMBF grants 01 IN 501 F & 01 KP 0006