OPTIMIZING SPATIO-TEMPORAL RESOLUTION AND POWER CONSUMPTION OF ELECTRICAL RETINA IMPLANT STIMULATION FROM RESPONSES OF CAT VISUAL CORTEX
T. Schanze1, R. Eckhorn1, M. Wilms1, M. Eger1. L. Hesse2, B. Nebeling2
A retina implant for restoring simple basic visual perception in patients that are blind due to photoreceptor loss requires optimization of stimulation parameters for high spatio-temporal resolution combined with low power consumption in animal models.
Methods: Semi-chronical methods for epi- and intraretinal stimulation in anesthetized cats were developed for optimizing spatio-temporal resolution of electrical microstimulations. Multiple microelectrodes as well as thin film electrodes were inserted using a manipulator into the cats eye through a small sclerotomy (about 1.1 mm diameter) without causing any sustaining harm. Electrodes were positioned under visual and recording control. Electrode properties were monitored to assure safe stimulation. Spatio-temporal distributions of charge balanced current impulses was varied including amplitude, duration and interpulse interval. Success of stimulation was controlled by recording multiple single cell and population activities &om the retina and area 17/18. Receptive fields of retinal and cortical sites were mapped in order to distinguish between corresponding and non-corresponding retinal stimulation and cortical recording sites.
Results: Threshold of electrical retina stimulation depended on the distance between the tip of the electrode and the retinal surface (lowest thresholds 5 pA). Cortical responses were related to duration, polarity and interpulse interval of the biphasic current impulses. Threshold was significantly lower for impulse trains than for single impulses. By first deflection analysis of cortical local field potentials magno-and parvocellular stimulation could be separated.
Conclusions: The experimental setting described is sufficient to optimize electrical stimulation for high resolution at minimal power consumption which is mandatory for long-term and safe stimulation.
(Supported by BMBF, grant 01 IN 501 F to R.E. and L.H.)
1Dept. of Neurophysics, Philipps-University, Renthof 7, D-35032 Marburg
2Dept. of Ophthalmology, Philipps-University, Robert-Koch-Str. 4, D-35033 Marburg