Electromigration driven void motion is studied in Ag wires with an initially well-defined single crystal lattice by in situ scanning electron microscopy. Voids are moving in opposite direction to the electron flow. When the electron current is reversed, voids exactly retrace their previous motion path with an increased drift velocity: The microstructure of the Ag wire "remembers" the motion path of the initial voids. To investigate the nature of this memory effect, we analyzed the crystal lattice with electron backscatter diffraction after passing of a void. The results show a permanent lattice degradation caused by the moving void. The implication of this finding for the reversibility of EM will be discussed. © 2014 AIP Publishing LLC.