The Imaginary Mind of a Mouse

Can the brain combine a previous memory into a current situation, creating the memory of an imaginary experience? It is commonplace to say teasingly of others that they live in an imaginary world. They go about their daily life much as others, but their thoughts and recollections have a surreal air—as if they lived in a world that is some combination of their imagination and the objective events of the physical world around them. Consider an experiment that deliberately creates this scenario, in which memories formed reflect not only the objective physical context of the study, but also imaginary “internal” stimuli that have somehow been artificially induced in the subject. Such a study could provide insights into the subtle interactions in cognition that occur between representations of the physical world and our internal thoughts. On page 1513 of this issue, Garner et al. (1) use elegant chemical and genetic engineering technology to peer into this aspect of the mind of a mouse.