Can histology solve the riddle of non-functioning electrodes; factors influencing the biocompatibillity of brain machine interfaces.

Neural interfaces hold great promise to become invaluable clinical and diagnostic tools in the
near future. However, the biocompatibility and the long-term stability of the implanted interfaces are far
from optimized. There are several factors that need to be addressed and standardized when improving
the long-term success of an implanted electrode. We have chosen to focus on three key factors when
evaluating the evoked tissue responses after electrode implantation into the brain: implant size,
fixation mode, and evaluation period. Further, we show results from an ultrathin multichannel wire
electrode that has been implanted in the rat cerebral cortex for 1 year.
To improve biocompatibility of implanted electrodes, we would like to suggest that free-floating, very
small, flexible, and, in time, wireless electrodes would elicit a diminished cell encapsulation. We would
also like to suggest standardized methods for the electrode design, the electrode implantation method,
and the analyses of cell reactions after implantation into the CNS in order to improve the long-term
success of implanted neural interfaces.