We investigated the effect of activating a competing, artificially generated, neural representation on encoding of contextual fear memory. We used a cfos based transgenic approach to introduce the hM3Dq DREADD receptor into neurons based on their natural activity patterns. Neural activity can then be specifically and inducibly increased in the hM3Dq expressing neurons by an exogenous ligand. When an ensemble of neurons for one context (ctxA) was artificially activated during conditioning in a distinct context (ctxB), animals formed a hybrid memory representation. Reactivation of the artificially stimulated network within the conditioning context was required for retrieval of the memory. The memory was specific for the spatial pattern of neurons artificially activated during learning while similar stimulation impaired recall when not part of the initial conditioning
