Abstract
It has recently been proposed that short-term memory (STM) binding deficits might be an important feature of Alzheimer's disease (AD), providing a potential avenue for earlier detection of this disorder. By contrast, work in Parkinson's disease (PD), using different tasks, has suggested that the STM impairment in this condition is characterised by increased random guessing, possibly due to fluctuating attention. In the present study, to establish whether a misbinding impairment is present in sporadic late-onset AD (LOAD) and increased guessing is a feature of PD, we compared the performance of these patient groups to two control populations: healthy age-matched controls and individuals with subjective cognitive impairment (SCI) with comparable recruitment history as patients. All participants performed a sensitive task of STM that required high resolution retention of object-location bindings. This paradigm also enabled us to explore the underlying sources of error contributing to impaired STM in patients with LOAD and PD using computational modelling of response error.Patients with LOAD performed significantly worse than other groups on this task. Importantly their impaired memory was associated with increased misbinding errors. This was in contrast to patients with PD who made significantly more guessing responses. These findings therefore provide additional support for the presence of two doubly dissociable signatures of STM deficit in AD and PD, with binding impairment in AD and increased random guessing characterising the STM deficit in PD. The task used to measure memory precision here provides an easy-to-administer assessment of STM that is sensitive to the different types of deficit in AD and PD and hence has the potential to inform clinical practice.
Highlights
With ~45% of individuals aged >85 years being diagnosed with Alzheimer’s disease (AD) (Liu, Liu, Kanekiyo, Xu, & Bu, 2013), one of the key priorities of healthcare has become the identification of individuals using sensitive measures that can be administered relatively rapidly
In the present study we examined shortterm memory (STM) performance in patients with lateonset AD (LOAD) versus Parkinson’s disease (PD), subjective cognitive impairment (SCI) and healthy controls using a Imprecision Set Size 2 Guesses Set Size 2 Swaps
In line with previous research, we found a selective impairment of feature binding in the STM performance of patients with LOAD compared to all other tested groups (Fig. 3b)
Summary
With ~45% of individuals aged >85 years being diagnosed with Alzheimer’s disease (AD) (Liu, Liu, Kanekiyo, Xu, & Bu, 2013), one of the key priorities of healthcare has become the identification of individuals using sensitive measures that can be administered relatively rapidly. Much of the focus previously has been on long-term memory (LTM) or episodic memory, recent investigations have shown that patients with either familial AD (FAD) or lateonset AD (LOAD) can have significant deficits in shortterm memory (STM) (Guazzo, Allen, Baddeley, & Sala, 2020; Liang et al, 2016; Parra et al, 2009, 2010, 2011, 2015) These findings intersect with recent models of memory which propose that the medial temporal lobes (MTL) e and the hippocampus, a region often implicated relatively early in ADeis involved in LTM and plays a role in STM. Consistent with this proposal, several studies have provided evidence for binding deficits in STM in individuals with focal MTL lesions as well as those with AD (Della Sala, Parra, Fabi, Luzzi, & Abrahams, 2012; Koen, Borders, Petzold, & Yonelinas, 2016; Liang et al, 2016; Parra et al, 2010, 2011, 2009; Pertzov et al, 2013; Zokaei, Nour, et al, 2018)
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