Targeted memory reactivation during sleep to strengthen memory for arbitrary pairings

A powerful way to investigate memory consolidation during sleep utilizes acoustic stimulation to reactivate memories. In multiple studies, Targeted Memory Reactivation (TMR) using sounds associated with prior learning improved later memory, as in recalling locations where objects previously appeared. In the present experiment, we examined whether a variant of the same technique could strengthen memory for the locations of pairs of objects. Each sound was naturally connected to one object from each pair, but we hypothesized that both memories could be improved with TMR. We first asked participants to memorize each of 50 pairs of objects by associating the two objects with each other and with the sound of one of the objects (e.g., cat-meow). Next, objects were presented in unique locations on a grid. Participants learned these locations in an adaptive procedure. During an afternoon nap, 25 of the sounds were quietly presented. In memory tests given twice before and twice after the nap, participants heard the sound for each object pair and were asked to recall the name of the second object and the locations of both objects. Forgetting scores were calculated using the mean difference between pre-nap and post-nap spatial recall errors. We found less forgetting after the nap for cued compared to non-cued objects. Additionally, the extent of forgetting tended to be similar for the two members of each pair, but only for cued pairs. Results thus substantiate the potential for sounds to reactivate spatial memories during sleep and thereby improve subsequent recall performance, even for multiple objects associated with a single sound and when participants must learn a novel sound-object association.