Memory reconsolidation as a tool to endure encoding deficits in elderly

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.

Fig 1. Experimental paradigm.

(A) Experimental protocol. (B) Training (day 1) Part 1: The 15 sound-word associations were presented on the computer screen. The music image stands for the sound. The headphones image stands for the word presented in an auditory form. Part 2: The 15 associations were evaluated in two blocks. For each association, the sound and the first syllable of the associated word were presented and participants had to answer with the associated word aloud upon appearance of an image of a microphone on the screen. The correct answer was displayed written on the screen and via headphones. (C) Reactivation (day 2). Each sound was followed by the presentation of the first syllable of each word. Participants were instructed to answer with the associated word aloud every time the microphone appeared on the screen however, the microphone was never shown. This sequence was repeated until all associations were presented. (D) Testing (day 7). All the associations were tested. The sound was presented and participants had to answer with the associated word.

Fig 2. Reconsolidation memory strengthening.

(A) Mean percentage of correct responses at training ± SEM for young and older adults. (B) Absolute memory change mean (correct responses at training minus correct responses at testing) ± SEM for young and older adults.

Fig 3. Mean percentage of errors at testing session for young and older adults.

(A) Void type errors. (B) Intralist type errors. (C) Confusion type errors. *, p<0.05; #, p = 0.060.