A medical microelectrode has a front end, a rear end and a density at 20 °C of from 0.80 to 1.15. The electrode comprises any of: electrically conductive tubiform lead com prising or consisting of a metal and/or an electrically conductive polymer, the lead having an outer surface and a sealed lumen； electrically conductive wire lead comprising or consisting of a metal and/or an electrically conductive polymer, the lead having a surface and a buoyant element of a density of less than 1.0 attached to the surface.
