A medical microelectrode includes portions capable of movement relative to each other when implanted in or inserted into soft tissue, so as to increase or decrease their distance along the electrode. The electrode is at least partially embedded in a substantially rigid biocompatible matrix that is soluble or biodegradable a body fluid. Also disclosed are uses of the microelectrode; microelectrode bundles and arrays of microelectrode bundles and their uses; methods for inserting or implanting microelectrodes, microelectrode bundles and arrays of microelectrode bundles in soft tissue.