The discovery that activated iridium recording sites have impedance characteristics that are a function of the applied DC bias has led to the investigation of the effects of DC bias on the impedance properties of metals that are commonly used for neuronal recording. Each metal has its own preferred operating potential. An understanding of the basic properties of the microelectrodes should provide improved recording characteristics. Three dimension multicontact passive semiconductor microelectrodes, supplied by the University of Michigan, have been implanted in the arm area of the motor cortex of a primate that was trained to do a number of different wrist movement tasks. Unfortunately, different techniques that were employed to protect the silicon ribbon cable from stresses produced by closing the dura over the microelectrode arrays have all failed. A more robust lead design is required to allow closure of the dura over the microelectrodes. Two dimension multicontact passive semiconductor microelectrodes, implanted in the supplementary motor cortex of a primate were found to migrate through the cortex, even after months of implantation. Techniques are under investigation that may help to stabilize the location of the microelectrodes for long-term recording.
