No dual-task practice effect in Alzheimer's disease

Abstract

Diagnosis of Alzheimer's disease (AD) requires evidence of progressive decline in cognitive function. However, many tests used to assess cognitive function suffer from considerable practice effects, reducing their reliability. Several studies have reported that the ability to do two things at once, or dual tasking, is impaired in AD, but unaffected by healthy ageing. The apparent specificity of this impairment suggests that this assessment may be particularly useful in the early diagnosis of AD, but the reliability of this assessment remains unknown.Therefore, this study investigated simultaneous performance of digit recall and tracking tasks across six testing sessions, in eight people with AD, eight healthy older adults and eight healthy younger adults. The results found that dual task performance was unaffected by healthy ageing, but significantly impaired in AD, with no effect of repeated exposure. The absence of any improvements in performance despite increased familiarity with the task's demands suggests that not only is the dual task assessment well suited for monitoring progression over time, but also that dual tasking involves a specific cognitive function which is impaired in the AD brain.

From Cognitive Science to Dementia Assessment

“…On the other hand, in less severe patients and in healthy volunteers, many memory tests tend to show effects of improvement simply due to practice across repeated test sessions (e.g., Rabbitt, Diggle, Holland & McKinnes, 2004). This practice effect could mistakenly be interpreted as a benefit from a treatment (see discussion in Foley, Cocchini, Logie, & Della Sala, 2015). People who show early signs of memory deterioration do not necessarily go on to develop AD, and AD is not an inevitable consequence of aging: more than 50% of people who live into their 80s and 90s do not develop the disease, even if they show a decline in memory ability for other reasons.…”

“…An alternative approach to the development of cognitive markers has come from clinical and experimental evidence showing that patients in the early stages of AD have problems dealing with multiple sources of information (e.g., Della Sala, Foley, Parra & Logie, 2011;Foley et al, 2015;Logie, Cocchini, Della Sala, & Baddeley, 2004 breakdown in the ability to do so can undermine independent living. Holding and updating these rapid changes around us is thought to be a function of a system in the brain known as working memory (Baddeley, 2007;Baddeley & Logie, 1999;Logie, 2011) that can hold information for a few seconds and continually update its contents to help us reason, think, solve problems, navigate, hold conversations and generally interact with the world moment to moment.…”

Retiring the Central Executive

“…Cocchini, Logie, Della Sala & MacPherson, 2003;Della Sala, Cocchini, Logie & MacPherson, 2010;Foley, Cocchini, Logie & Della Sala, 2015;Logie, Cocchini, Baddeley & Della Sala, 2004;MacPherson, Della Sala, Logie & Wilcock, 2007;Ramsden, Kinsella, Ong & Storey, 2008;Sebastian, Menor and Elosua, 2006) while addressing potential criticisms of its interpretation, such as the argument that dual task is more difficult than single task for someone with a damaged brain.…”

Alzheimer's Disease: From Animal Models to the Human Syndrome

“…The 3xTg-AD, triple-transgenic model exhibits both Aβ and tau pathologies and mimics human AD [60]. Thus, the possible role of Aβ in AD cognitive decline needs to be further investigated, fueled by other possible hypotheses and explanations [57].…”

“…However, the relationships between Aβ levels (Aβ 40, A β42, or the ratio of Aβ 42 to Aβ 40), gender, age and cognitive function were measured in five mouse models (Tg2576, APP, PS 1, APP(OSK)-Tg, 3xTg-AD), see reference [57]. They used behavior tests such as escape latency times in the Morris water maze or exploratory preference percentage in the novel object recognition test.…”