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PSYCHOGERIATRICS 2014; 14: 63–71

doi:10.1111/psyg.12042

ORIGINAL ARTICLE

Lowered performance in working memory and attentional sub-processes are most prominent in multi-domain amnestic mild cognitive impairment subtypes Shannon Z. KLEKOCIUK1 and Mathew J. SUMMERS1,2

1

School of Psychology, University of Tasmania, Launceston, and 2Wicking Dementia Research & Education Centre, Menzies Research Institute Tasmania, Hobart, Tasmania, Australia Correspondence: Dr Mathew J. Summers BBehavSc(Hons) MPsych(ClinNeuropsych) PhD, School of Psychology, University of Tasmania, Locked Bag 1342, Launceston, Tas. 7250, Australia. Email: [email protected] Received 12 September 2013; revision received 17 October 2013; accepted 12 December 2013.

Key words: attention, mild cognitive impairment, neuropsychological, working memory.

Abstract Background: Research suggests that working memory and attention deficits may be present in mild cognitive impairment (MCI). However, the functional status of these domains within revised MCI subtypes remains unclear, particularly because previous studies have examined these cognitive domains with the same tests that were used to classify MCI subtypes. The aim of this study was to examine working memory and attention function in MCI subtypes on a battery of neuropsychological tests that were distinct from those used to classify MCI subtypes Methods: A total of 122 adults aged 60–90 years were classified at baseline as amnestic MCI, non-amnestic MCI, and multi-domain amnestic (a-MCI+). The attentional and working memory capacity of participants was examined using a battery of tests distinct from those used to classify MCI at screening. Results: The a-MCI+ group demonstrated the poorest performance on all working memory tasks and specific sub-processes of attention. The nonamnestic MCI group had lowered performance on visual span and complex sustained attention only. There was no evidence of either attentional or working memory impairment in the amnestic MCI participants. Conclusion: When MCI cohorts are assessed on measures distinct from those used at classification, a-MCI+ subjects had the most compromised working memory and attention function. These results support previous findings that suggest a-MCI+ more closely resembles early stage Alzheimer’s disease and those with a-MCI+ may be at increased rate of future cognitive decline compared to those with other MCI subtypes.

INTRODUCTION Examination of the cognitive profile of early Alzheimer’s disease (AD) suggest that deficits to episodic memory do not occur in isolation, but in conjunction with subtle deficits to executive functions, such as attention and working memory.1–4 More recently, there has been evidence to suggest that the presence of attention and working memory deficits may predate episodic memory dysfunction in AD or indicate the imminent decline to dementia in individuals with pre-clinical AD who present with episodic memory dysfunction.5,6,7 Evidence of working memory and attention compromise has also been demonstrated in © 2014 The Authors Psychogeriatrics © 2014 Japanese Psychogeriatric Society

individuals classified with mild cognitive impairment (MCI).4,8 This suggests working memory and attention function may play an important role in understanding the trajectory of cognitively impaired but not yet demented older adults. In a recent study, Saunders and Summers reported longitudinal deterioration to multiple sub-processes of attention in non-amnestic MCI (na-MCI) subjects, including multi-domain na-MCI (na-MCI+) subjects, and in amnestic MCI (a-MCI) subjects, including multidomain a-MCI (a-MCI+) subjects, with the a-MCI group displaying prominent deficits to divided attention.8 In addition, na-MCI and a-MCI groups were 63

S. Z. Klekociuk and M. J. Summers

found to have stable impairments to visual working memory. Belleville et al. also reported deficits to working memory and attention in an MCI sample (combined a-MCI and a-MCI+).4 This led them to suggest that divided attention may show early compromise in MCI, which is followed by difficulty with manipulating information in short-term memory. While these studies suggest that attention and working memory deficits are present in MCI, it is less clear if this profile is maintained when cohorts are comprehensively assessed on valid and reliable neuropsychological tests and on a battery that is distinct from that used to establish MCI classifications. The importance of comprehensively assessing memory and non-memory function in potential MCI cases has been acknowledged.8,9 Previous research has demonstrated that MCI cases can be missed or misclassified if broad global measures are used to infer the integrity of non-memory domains.10,11 As a result, comprehensive neuropsychological assessment is emerging as the gold standard procedure to maximise the sensitivity and specificity of MCI classifications. Furthermore, some researchers have classified and examined cognitive profiles in MCI using the same battery of neuropsychological tests. It has been argued that this creates a self-fulfilling prophecy in MCI classification.12,13 If individuals presenting with performance decrements on specific neuropsychological tests are classified as MCI, then it is hardly surprising that cross-sectional analysis of their profiles reveals lowered performances within these domains. To reduce the potential influence of circular reasoning, it has been suggested that MCI research should employ a test battery to classify individuals with MCI that is distinct from the one used to examine individuals’ cognitive profile.14 The aim of the present study was to clarify the working memory and attention profile of MCI subtypes using a comprehensive test battery distinct from the one used to classify individuals at screening. The findings reported here refer to a cohort classified at screening as amnestic, non-amnestic, multipledomain amnestic, or control.15 This approach will provide greater understanding of the working memory and attention function of MCI subtypes while reducing the potential influence of circular reasoning. In line with the current conceptualization of MCI subtypes, it was hypothesized that a-MCI and na-MCI participants will display poorer performance on attention 64

and working memory tasks than the control and a-MCI groups.

METHOD Study population The participants in this study were a sample of community-residing adults recruited in 2010 as part of a longitudinal study tracking the neuropsychological profile of MCI. Participants were recruited on the basis of the following criteria: (i) presence of cognitive complaints (e.g. memory, attention); (ii) preserved general cognition (as assessed by the Dementia Rating Scale, second edition); (iii) self-reported capacity to maintain independent daily functioning (confirmed by an informant); (iv) no history of major medical, neurological, or psychiatric illness (medical screening questionnaire); (v) no history of major risk factors for vascular disease (medical screening questionnaire); and (vi) no history of sensory impairment or impairment to hand mobility.8,16,17 Each participant provided informed consent prior to the commencement of the study in accordance with the Human Research Ethics Committee (Tasmania) Network, the National Health and Medical Research Council of Australia Human Research Guidelines and the Helsinki Declaration. From initial recruitment and pre-screening (n = 286), a total of 200 participants were screened via a comprehensive neuropsychological test battery to classify participants according to existing MCI criteria and previous published research (Table 1).8,15,17 Thirty-one participants were excluded from data analysis and further assessment due to various psychological and medical reasons not disclosed at telephone screening. A total of 169 participant results were included in the screening cohort (66 men, 103 women). Participants were all of British or European decent. Subclinical impairment was defined as a performance 1.28 SD or greater (

Lowered performance in working memory and attentional sub-processes are most prominent in multi-domain amnestic mild cognitive impairment subtypes.

Research suggests that working memory and attention deficits may be present in mild cognitive impairment (MCI). However, the functional status of thes...
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