|Author(s)||Greve N. (1), Schanze T. (1), Eger M. (1), Eckhorn R. (1), Wilms M. (1) & Hesse L. (2)|
|Addresse(s)||(1) NeuroPhysics Grp., Philipps-University Marburg, Germany; (2) Dept. Ophthalmology, Philipps-University Marburg, Germany|
|Title||Transmitting form and motion from retina implants to the visual cortex of cats.|
|Text||Focal electrical stimulation of the retina can evoke localized phosphenes
in blinds with photoreceptor degeneration  so that residual vision may
become possible. Our present goal is to explore the possibilities and achievable
resolutions for form and movement information by retina implants in intact
anaesthetized cats. We tested the success of generating electrically form
and movement representations in primary visual cortex (V1) by recordings
of neural response profiles in V1. In our recent work in, we obtained estimates
of spatial and temporal resolutions for a focal electrical stimulus (about
1° and 20 ms, respectively ). In the present study fibre electrodes were
inserted through a small scleral incision onto the retinal surface for stimulation.
In addition, we tested foil electrode arrays implanted epiretinally or subretinally
between bipolar cells and pigment epithelium near the central retinal area.
Retinal and cortical electrodes had corresponding visual locations, i. e.,
their visual receptive fields largely overlapped. Electrical stimuli were
charge balanced impulses (50 to 1000 µs; 1 to 500 µA). Different basic form
stimuli were constructed by positioning the tips of retinal electrodes systematically
at different distances and angles and activating them synchronously. Basic
movement stimuli were generated by translating the form stimuli to a second
retinal position at various distances and delays, mimicking different velocities.
We recorded spike activities and local field potentials (LFP) by an array
of microelectrodes in V1. From the spatio-temporal activation profiles we
estimated the relations between stimulation distance and angular resolution
(form) and between spatial resolution and velocity (movement).
 MS Humayun et al (1996) Arch Ophthalmol 114: 40-46,  Schanze et al (2001) submitted.
(Support by BMBF grant 01 KP 0006 to RE, LH, and TS is greatly acknowledged).
Vision / Striat visual cortex: Neural coding and synchrony