No dual-task practice effect in Alzheimer's disease

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 dualtask
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.