Unrelated memories can be artificially linked by activating distinct groups of neurons at the same time.

Kaoru Inokuchi at the University of Toyama, Japan, and his colleagues let mice explore a cylindrical container. Later they placed the mice in a cubic box and gave them an immediate electric shock to the foot. The scientists then used light to stimulate those neurons in the hippocampus and amygdala regions of the mouse brain that had been activated both when the animals had laid down their memories of the safe cylindrical container and when they received the electric shock in the box.

When light-stimulated mice were placed back in the cylinder, they froze for a longer time than mice that did not receive brain stimulation, suggesting that the stimulated mice connected the shock with the safe environment.

Cell Rep. http://dx.doi.org/10.1016/j.celrep.2015.03.017 (2015)