WORKING MEMORY FILTERING AT ENCODING AND MAINTENANCE IN HEALTHY AGEING, ALZHEIMER’S AND PARKINSON’S DISEASE

The differential impact on working memory (WM) performance of distractors presented either at encoding or during maintenance was investigated in Alzheimer’s (AD), Parkinson’s Disease (PD) and healthy ageing. Across three studies, 28 AD and 28 PD patients, 28 elderly (EHC) and 28 young healthy controls (YHC) were enrolled. All participants performed a delayed reproduction task, where they reported the orientation of an arrow from a study set of either two or three items, with a distractor present either at encoding or at maintenance. Mean absolute error (the difference between probed and reported orientation) was calculated as an analogue measure of WM. Additionally, mixture model metrics i.e., memory precision, target detection, misbinding (swapping the features of an object with another probed item) and guessing were computed. MRI data was also acquired in AD, PD and EHC participants, and whole hippocampal volumes were extracted to test whether WM filtering and overall performance were related to hippocampal integrity.

EHC and PD patients showed good filtering abilities both at encoding and during maintenance. However, AD patients exhibited significant filtering deficits specifically when the distractor appeared during maintenance. Healthy ageing and AD were associated with higher rates of both misbinding and guessing, as well as lower target detection, and memory precision. However, in healthy ageing there was a prominent decline in WM memory precision, whilst in AD lower target detection and higher guessing were the main sources of error. Conversely, PD was associated only with higher guessing rates. Hippocampal volume was significantly correlated with filtering during maintenance – but not at encoding – as well as with overall mean absolute error, target detection, guessing and misbinding. These findings demonstrate how healthy ageing and neurodegenerative diseases exhibit distinct patterns of WM impairment, including differential effects on filtering irrelevant material presented at encoding and maintenance.