Exploring the sensitivity of episodic and spatial memory tests to healthy and pathological cognitive aging

In an increasingly aging society, testing hippocampal-dependent cognition in a quick and low resource manner will be crucial in: assessing the potential benefits of lifestyle choices and interventions affecting cognitive ageing (such as those involving exercise, diet, and sleep); detecting pathological aging, such as in Alzheimer's disease, where hippocampal degeneration occurs relatively early on.

Over 300 participants aged 18-89 completed three cognitive tests, namely the Addenbrooke's Cognitive Examination-III (ACE-III), The Four Mountains Task (4MT), and a new task introduced here, the Spaces and Sequences Episodic Video Task (SSEVT). Hippocampal tissue is particularly vulnerable to aging, and the 4MT and SSEVT were designed to be hippocampal-dependent. Accordingly, we tested the hypothesis that 4MT and SSEVT performance would be significantly compromised by aging. As an initial proof-of-concept exploration of these tests' ability to detect pathological aging, such as in Alzheimer's disease, we compared 10 patients with Mild Cognitive Impairment (MCI) with matched subsamples of the older group (Healthy ageing, HA).

Supporting the hippocampal-aging related hypothesis, 4MT and SSEVT scores showed appreciably stronger age-related declines than ACE-III scores. The middle-aged group (mean: ∼51 years) were significantly worse than the young group (mean: ∼21 years) on the 4MT (Cohen's d = 0.724) and the SSEVT (Cohen's d = 0.443); and the older group (mean: ∼71 years) were significantly worse than the middle-aged group on the SSEVT (Cohen's d = 0.724). Neither pattern was seen for ACE-III. Suggestively, the MCI patients performed worse than the matched HA group on the 4MT (consistent with previous work), and on our novel SSEVT, but not on the ACE-III.

We conclude that the 4MT and SSEVT may be suitable for assessing lifestyle choices and interventions affecting cognitive ageing. We also propose that these findings provide an initial proof-of-concept for these tests' ability to detect pathological aging in its early stages and support further exploration of this with larger clinical samples.