Before revision:  These signals originate in highly invariant neurons, which uniquely respond to some specific stimuli , e.g. image of a cat , and travel backwards to reactivate the same populations of neurons that usually uniquely activate in the actual presence of such specific stimuli , thus creating offline an experience that is similar.
After revision:  These signals originate in highly invariant neurons, which uniquely respond to some specific stimuli , e.g. image of a cat ). They then travel backwards to reactivate the same populations of neurons that usually uniquely activate in the actual presence of such specific stimuli , thus creating offline an experience that is similar.