Accelerated forgetting in healthy older samples: Implications for methodology, future ageing studies, and early identification of risk of dementia

Abstract

Accelerated long-term forgetting (ALF) has been reported in healthy older individuals, and is a possible early marker for risk of developing Alzheimer's disease (AD). The Verbal Associative Learning and Memory Test (VALMT) addresses methodological weaknesses in existing clinical tests and has detected ALF in epilepsy within an hour. We used VALMT to investigate learning and forgetting in healthy Older participants. Older (60-69 years) and Younger (19-31 years) participants were compared. Using VALMT, unrelated word pairs were learnt to criterion, then cued-recall tested at delays of 5, 30, and 55 min. Unique pairs were tested at each delay. Subjective memory complaints data was gathered, and the Wechsler Memory Scale Logical Memory test (WMS-LM; a standard clinical measure) was administered. VALMT identified a significant difference in delayed recall between Younger and Older groups by 55 min (d = 1.32). While "fast-learning" Older participants scored similarly to Younger participants, "slow-learning" Older participants were impaired at all delays. Forgetting rates suggested degradation of memory starts during early synaptic consolidation rather than later system-level consolidation. Increased subjective memory complaints were associated with reduced VALMT scores. By contrast, WMS-LM failed to identify significant differences between any groups, and did not correlate with memory complaints. We conclude that VALMT may be better able than WMS-LM to identify subtle impairments in healthy older adults within a single clinical visit, and VALMT results better reflect subjective experience. Older slow-learners forget faster and report more subjective memory complaints, which may indicate a group at risk of developing AD.

Keywords: Accelerated long-term forgetting; accelerated forgetting; ageing; consolidation; forgetting rates.

Figure 1.

Learning and testing schedule.

Figure 2.

Mean VALMT recall scores as a function of time delay and group (error bars represent one standard error).

Figure 3.

Mean VALMT recall scores as a function time delay and group, separating the Older group into two groups based on initial learning (error bars represent one standard error).

Figure 4.

Mean WMS-LM recall scores as a function of time delay and group (error bars represent one standard error).

Figure 5.

Mean WMS-LM recall scores as a function time delay and group, separating the Older group into two groups based on initial learning (error bars represent one standard error).

Figure 6.

Sleep quality total score as a function of Group, with Older participants shown as a combined group and separated into two groups based on initial learning (error bars represent one standard error).

Figure 7.

Memory complaints total score as a function of Group, with Older participants shown as a combined group and separated into two groups based on initial learning (error bars represent one standard error).

Figure 8.

Mean VALMT recall scores as a function time delay and Group, separating the Older group into two groups based on memory complaints (error bars represent one standard error).

Figure 9.

Mean WMS-LM recall scores as a function time delay and Group, separating the Older group into two groups based on memory complaints (error bars represent one standard error).