Objective: Intraindividual variability (IIV) in reaction time refers to the trial-to-trial fluctuations in responding across a given cognitive task. Cross-sectional research suggests that IIV increases with normal and neuropathological ageing and it may serve as a marker of neurobiological integrity. This raises the possibility that IIV may also predict future cognitive decline and, indeed, neuropathology. Therefore, we conducted a systematic review to address these issues. It is well established that adult ageing is characterised behaviourally by increased intraindividual variability in cognitive function. As the present review will show, such variability is not only a feature of normal ageing, but becomes more marked in the presence of neuropathology or impending mortality. It is likely that this widely observed behavioural characteristic of ageing reflects greater neurobiological variability stemming from compromised central nervous system integrity. Given the proposed neurobiological underpinnings of IIV, the aim of the present systematic review, therefore, was to critically evaluate the empirical literature using this marker to predict cognitive change in normal ageing, and also age-related neuropathological outcomes including mild cognitive impairment (MCI), dementia, Parkinson's disease and, indeed, death. First though, we describe some of the characteristics of this behavioural marker before detailing theoretical and empirical linkage to potential underlying neurobiological variability.

No abstract

Despite cognitive or psychiatric problems, our patient group are as likely to own a mobile phone as a member of the general population. Ownership levels are at 40% and likely to increase in the future. Exploring how smartphones and their apps could function as memory aids is likely to be useful for a large enough number of patients to be clinically worthwhile.

In old age, a relationship has been reported between intraindividual variability (IIV) in reaction time and white matter integrity as evidenced by white matter hyperintensities (WMH). However, it is unclear how far such associations are due to incipient neurodegenerative pathology in the samples investigated. The present study examined the relationship between IIV and WMH in older individuals (N=526) drawn from the Sydney Memory and Ageing Study. Using a complex reaction time (RT) task, greater IIV and mean-RT were related to a higher WMH burden in the frontal lobe. Critically, significant associations remained having taken future dementia into account suggesting that they were not explained by incipient dementia. Additionally, independent measures of executive function accounted for the association between RT metrics and WHM. The results are consistent with the view that frontally-supported cognitive processes are involved in IIV-WMH relations, and that RT measures are sensitive to compromise in white matter structures in non-demented older individuals.Key words, white matter hyperintensities, reaction time, intraindividual variability, executive function, cognition.RT variability and WMH in old age 3 IntroductionIntraindividual variability (IIV), or inconsistency (e.g., Hultsch, MacDonald, & Dixon, 2002), refers to within-person variation in cognitive performance over time, and is often measured by the trial-by-trial variation in reaction times (RT) for a given cognitive task. It is well established that ageing is accompanied by cognitive decline and slowing of processing speed (e.g., Salthouse, 2010). However, an accumulating body of research suggests older adults are also more variable than younger adults (e.g., Bielak, Cherbuin, Bunce, & Anstey, 2014), even when response speed is taken into account (Dykiert, Der, Starr, & Deary, 2012). One proposal holds that IIV is an early indicator of neurobiological disturbance (Hultsch, MacDonald, Hunter, Levy-Bencheton, & Strauss, 2000;Hultsch, Strauss, Hunter, & MacDonald, 2008). In support of this, greater variability is evident in individuals with agerelated disorders such as mild cognitive impairment and dementia (Christensen et al., 2005;Duchek et al., 2009;Gorus, De Raedt, Lambert, Lemper, & Mets, 2008;Hultsch et al., 2000;Strauss, Bielak, Bunce, Hunter, & Hultsch, 2007), Parkinson's disease (de Frias, Dixon, Fisher, & Camicioli, 2007) and also frontal lobe lesions (Stuss, Murphy, Binns, & Alexander, 2003).Given the suggestion that IIV is an indicator of neurobiological disturbance, a number of magnetic resonance imaging (MRI) studies have investigated the link between variability and structural brain measures. In healthy ageing, associations have been shown between IIV and white matter hyperintensities (WMH: Bunce et al., 2010;Bunce et al., 2007), white matter volume (Jackson, Balota, Duchek, & Head, 2012;Lovden et al., 2013;Ullen, Forsman, Blom, Karabanov, & Madison, 2008;Walhovd & Fjell, 2007) and diffusion tensor imaging metrics (e.g., FA -fractional...

Article:Haynes, BI orcid.org/0000-0003-0054-6591, Kliegel, M, Zimprich, D et al. (1 more author) (2018) Intraindividual reaction time variability predicts prospective memory failures in older adults. Aging, Neuropsychology, and Cognition, 25 (1 ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Running head -IIV PREDICTS PROSPECTIVE MEMORY FAILURES AcknowledgementsThe research received financial support from the Swiss National Science Foundation. We are grateful to Melanie Zeintl for comments on a previous version of this manuscript. IIV PREDICTS PROSPECTIVE MEMORY FAILURES 2 AbstractThis study investigated the relationship between intraindividual variability (IIV) in reaction time and prospective memory errors in older adults using data from the Zurich Longitudinal