Memories as subjective experiences are encoded in the brain by distributed populations of neurons.In order to study the formation, dynamics and decay of memory traces (engrams) they have to be visualized.We have previously found that consolidation of such functional systems involves neuronal expression of immediate-early genes (IEGs)(Maleeva et at., 1989) and that this expression can be used to map memory assemblies in the brain (Anokhin, 1989).Behavioral induction of IEGs is triggered by subjective novelty of experience (Anokhin & Sudakov, 1993) and occurs during establishment of single-trial episodic-like memories (Anokhin et al., 1991;Ryabinin & Anokhin, 1993).