No abstract

Normal aging involves changes in the ability to acquire, consolidate and recall new information. It has been recently proposed that the reconsolidation process is also affected in older adults. Reconsolidation is triggered after reminder presentation, allowing memories to be modified: they can be impaired, strengthened or changed in their content. In young adults it was previously shown that the presentation of repetitive reminders induces memory strengthening one day after reactivation and the presentation of at least one reminder increases memory persistence several days after reactivation. However, until now this process has remained elusive in older adults. We hypothesize that older adults need a stronger reminder to induce memory strengthening through the reconsolidation process than young adults. To test this, we perform a three-day experiment. On day 1, participants learned 15 sound-word associations, on day 2 they received no reminders (NR group), one reminder (R group) or two rounds of reactivations (Rx2 group). Finally, they were tested on day 7. We found that, contrary to our hypothesis, older adults show a memory improvement triggered by repeated labilization/reconsolidation processes to an equal extent than young adults. These results open new perspectives into the use of reconsolidation to improve daily acquired information and the development of therapeutic home used tools to produce memory enhancement in healthy older adults or those with cognitive decline.

Consolidated memory can be again destabilized by the presentation of a memory cue (reminder) of the previously acquired information. During this process of labilization/restabilization memory traces can be either impaired, strengthened or updated in content. Here, we study if a consolidated memory can be updated by linking one original cue to two different outcomes and whether this process was modulated by the GABAergic system. To aim that, we designed two experiments carried out in three consecutive days. All participants learned a list of non-sense syllable pairs on day 1. On day 2 the new information was introduced after the reminder or no-reminder presentation. Participants were tested on day 3 for the updated or original list (Exp. 1). In Exp. 2 we tested whether this new information was incorporated by an inhibitory process mediated by the GABAergic system. For that, participants retrieved the original information before being taken Clonazepam 0.25mg (GABA agonist) or Placebo pill. We found that the groups that received the reminder correctly recalled the old and new information. However, the no reminder groups only correctly recalled the original information. Furthermore, when testing occurred in the presence of Clonazepam, the group that received the reminder plus the new information showed an impaired original memory performance compared to the group that received only Clonazepam (without reminder) or the reminder plus Placebo pill. These results show that new information can be added to a reactivated declarative memory in humans by linking one cue to two different outcomes. Furthermore, we shed light on the mechanisms of memory updating being the GABAergic system involved in the modulation of the old and new information expression.