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Behavioural Neurology 23 (2010) 177–179 DOI 10.3233/BEN-2010-0288 IOS Press

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Working memory in Alzheimer’s disease and frontotemporal dementia
C.L. Stopford∗ , J.C. Thompson, A.M.T. Richardson, D. Neary and J.S. Snowden
Greater Manchester Centre for Neurosciences, Salford, UK

1. Background Working memory deficits are a recognised feature of Alzheimer’s disease (AD) and can bedissociated from episodic memory impairment, with distinct patterns of breakdown in individuals [1]. Distinctions in clinical profile may have neurobiological relevance. We have previously shown [2] that patients presenting with a dense yet relatively circumscribed classical amnesia (“amnestic-AD”, accounting for 10% in a series of 523 patients) were older and more likely to carry apolipoprotein ε4alleles than those presenting with a constellation of working memory, language and perceptuospatial deficits (labelled “typical- AD” on the basis that they accounted for 61% of cases). Such findings highlight the importance of careful characterisation of individual patients in experimental research. A goal of the present study was to understand the working memory deficit in AD whilst recognising theseimportant distinctions. Existing research focuses on difficulties on dual-task paradigms, encouraging the notion of central executive dysfunction, and promoting a relationship between working memory deficits and frontal lobe pathology in AD [3]. Failures on standard tests of attention and executive function reinforce this interpretation. However, characteristic neuroimaging changes in early onset AD arein posterior hemispheres rather than frontal lobes. Moreover, ‘frontal’ behavioural characteristics are absent. Characteristic qualities of persistence, motivation, and concern for accuracy contrast markedly with the economy of effort and lack of engagement demonstrated by patients with frontotemporal dementia (FTD), the prototypical neurodegenerative disease of the frontal lobes. The presence ofqualitative differences in cognitive profile [4] suggests that
∗ Corresponding

there are distinct contributions to performance failure. We took the novel approach of exploring the frontal dysexecutive contribution to working memory by comparing test performance in patients with AD and FTD. If the basis of the impairment is primarily ‘frontal dysexecutive’, then one would expect similar profilesin the two groups. However given the ‘posterior’ abnormalities shown on AD patients’ imaging and absence of ‘frontal’ behavioural signs, we predicted that there ought to be qualitative differences on tests of working memory, attention, and executive function.

2. Participants In line with our earlier work [2], the main focus were “typical” patients (n = 20; age 52–68) presenting with aconstellation of cortical symptoms. Those with a circumscribed “amnesic” presentation (n = 18; age 59–83) were included as a reference group. AD patients were classified based on clinical history of symptoms obtained at initial diagnostic assessment and performance on a locally developed neuropsychological screening assessment. There were no significant differences between the AD and FTD patients (n = 26;age 52–76) with regard to illness duration (4–6 years) or Clinical Dementia Rating scale score (CDR 1: mild). Clinical neuroimaging showed characteristic temporoparietal change in typical-AD, medial temporal changes in amnesic-AD, and frontal lobe abnormalities in FTD.

3. Methods Tasks were administered to examine working memory (a modified Brown-Peterson test involving memory for three wordswith and without delay/distraction;

author. E-mail: Cheryl.Stopford@manchester.

ac.uk.

ISSN 0953-4180/10/$27.50 © 2010 – IOS Press and the authors. All rights reserved

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Table 1 Result Typ-AD < FTD < Amn-AD = control Typ-AD < FTD = Amn-AD = control Typ-AD < FTD = Amn-AD = control Typ-AD < FTD < Amn-AD = control Typ-AD = FTD < Amn-AD = control FTD > Typ-AD Typ-AD < FTD < Amn-AD =...