Behavioral tagging and capture: long-term memory decline in middle-aged rats.

Alexandra Gros,Szu-Han Wang

doi:10.1016/j.neurobiolaging.2018.02.023

Abstract

Decline in cognitive functions, including hippocampus-dependent spatial memory, is commonly observed at a later stage of aging (e.g., >20 months old in rodents) and typically studied after a discrete learning event. How normal aging, particularly at an early stage, affects the modulatory aspect of memory persistence is underinvestigated. Previous studies in young animals show that weak, fading memories can last longer if a modulating event, such as spatial novelty, is introduced around memory encoding. This is known as behavioral tagging and capture (BTC). Here, we investigated how early aging (10–13 months old) affects BTC in an appetitive delayed-matching-to-place task. We trained rats when they were young and middle aged and found that novelty facilitated long-term memory persistence in young but not in middle-aged rats. However, re-exposure to the encoded environment after learning improved memory persistence in middle-aged rats. BTC, combined with memory reactivation, facilitated memory persistence through reconsolidation. Our results point toward a weakened tagging and capture mechanism before reduction of plasticity-related proteins at an early stage of aging.

Highlights

Aging is a natural biological process associated with a decline in cognitive function (Leal and Yassa, 2015)
Our results suggest that the behavioral tagging and capture process is deteriorating during cognitive aging, which contributes to poor memory persistence
To differentiate whether it is the tagging process or the proteins or products (PRPs) production that is primarily impaired at the middle age, we found that a second strong encoding trial or a nonrewarded exposure in the encoded zone were able to improve long-term memory persistence

Summary

Introduction

Aging is a natural biological process associated with a decline in cognitive function (Leal and Yassa, 2015). Deficits in navigational strategy, spatial memory, pattern separation, and reductions in working memory capacity are observed during normal aging in animals (Bach et al, 1999; Barnes, 1979; Creer et al, 2010; Cès et al, 2018; Dunnett et al, 1988; Lacreuse et al, 2014; Markowska et al, 1989; Rapp et al, 1997). To describe the mechanisms affected by the early phase of aging, we used a behavioral tagging and capture paradigm. This provides a method for dissociating the process of encoding the memory of interest and the facilitation of memory persistence by a memory-modulating event (MME)

Methods

Results

Discussion

Conclusion