We observed two types of resistance oscillatory changes, downward spikes and upward spikes, which occurred abruptly during direct current electromigration in a polycrystal A1 interconnection. These spikes are further classified into quasi-periodic and random ones. Investigation of the current density dependence revealed that the frequency of the downward spikes drastically increased with increasing current density, while the amplitude of upward spikes increased drastically. We also determined that downward spikes were local, while upward spikes werenonlocal. Modeling based on the annihilation and formation of a void and the current detour effect around thehigh-resistance region well explained the current density dependence of the frequency of the oscillations. It seemsmost likely that downward spikes correspond to the alternation of annihilation and formation of the single void, while dislocation dynamics such as generation and annihilation are candidates for the origins of the upward spikes.