When reactivated, memories enter a labile, protein synthesis dependent state, a process referred to as reconsolidation. Here, we show in rats that fear memory retrieval produces a synaptic potentiation in the lateral amygdala that is selective to the reactivated memory, and that disruption of reconsolidation is correlated with a reduction of synaptic potentiation in the lateral amygdala. Thus, both retrieval and reconsolidation alter memories via synaptic plasticity at selectively targeted synapses.