1. Field of the Invention
The present invention relates generally to electrode systems for stimulation or monitoring electrical activity in nerve tissue and more particularly relates to chronically implantable electrodes.
2. Description of the Prior Art
The use of electrodes to monitor electrical activity and stimulate body tissue is quite old. R. H. Wappler U.S. Pat. No. 1,662,446 teaches an early electrode system. The Wappler electrode is used for acute stimulation only, and is not implantable.
An early stimulation electrode which is chronically implantable is taught by S. I Schwartz, et al. in U.S. Pat. No. 3,421,511. Hagfors U.S. Pat. No. 3,654,933 teaches an improved stimulation electrode for chronic implantation.
Testerman U.S. Pat. No. 4,341,221 teaches an improved electrode for chronic implantation. The Testerman electrode is suitable for monitoring electrical activity in nerve tissue. This electrode uses a substrate of silicone rubber or other material which is inert when chronically implanted. However, as with the other electrodes, the Testerman electrode does not prevent excess fibrotic growth.