Findings from epidemiological and observational studies have indicated that diets high in omega-3 polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) may reduce the risk of cognitive decline and Alzheimer’s disease (AD). To determine if increasing intake of DHA and EPA through supplementation is beneficial to cognition and mood in individuals with cognitive impairment no dementia (CIND) or Alzheimer’s disease (AD) a four month, randomised, double-blind, placebo controlled study was conducted. Fifty-seven participants with CIND and nineteen with AD were randomised to receive either omega-3 PUFAs (600 mg EPA and 625 mg DHA per day) or placebo (olive oil) over a four month period. Elevating depleted levels of EPA and DHA through supplementation in individuals with CIND or AD was found to have negligible beneficial effect on their cognition or mood. These findings confirm an overall negligible benefit of omega-3 PUFA supplementation for those with cognitive impairment and dementia. More intervention studies need to be undertaken with longer study durations and larger sample sizes. It may prove fruitful to examine effects of different doses as well as effects in other dementia subtypes.

Compared to cognitively healthy ageing (CH), intra-individual variability in reaction time (IIVRT), a behavioural marker of neurological integrity, is commonly reported to increase in both Alzheimer’s disease (AD) and mild cognitive impairment (MCI). It varies in MCI with respect to whether it represents the pro-dromal stages of dementia or not; being greatest in those most likely to convert. Abnormal IIVRT in MCI therefore represents a potential measure of underlying functional integrity that may serve to differentiate MCI from CH and to help identify those patients for whom MCI is the result of a progressive pathological process. As the clinical approach to MCI is increasingly stratified with respect to gender, we investigated whether this factor could influence study outcome. The influence of RTSPEED and processing load upon IIVRT was also examined. Under low processing load conditions, IIVRT was significantly increased in both MCI and AD compared to CH. However, correcting for an individual’s processing speed abolished this effect in MCI but not in AD, indicating that the increased IIVRT in MCI and AD may result from different factors. In MCI but not in CH, IIVRT was significantly greater for females. Increasing task processing load by adding distracting information, although increasing overall IIVRT, failed to improve the differentiation between CH and both MCI and AD, and in MCI resulted in a reduction in the influence of gender upon study outcome. The outcome of studies investigating IIVRT in MCI and AD compared to CH therefore appear influenced by the gender of the participants, by task-related processing load and processing speed.

A substantial body of research evidence is indicative of disproportionately slowed information processing speed in a wide range of multi-trial, computer-based, neuroimaging- and electroencephalography-based reaction time (RT) tests in Alzheimer’s disease and mild cognitive impairment (MCI). However, in what is arguably a dichotomy between research evidence and clinical practice, RT associated with different brain functions is rarely assessed as part of their diagnosis. Indeed, often only the time taken to perform a single, specific task, commonly the Trail making test (TMT), is measured. In clinical practice therefore, there can be a failure to assess adequately the integrity of the rapid, serial information processing and response, necessary for efficient, appropriate, and safe interaction with the environment. We examined whether a typical research-based RT task could at least match the TMT in differentiating amnestic MCI (aMCI) from cognitively healthy aging at group level. As aMCI is a heterogeneous group, typically containing only a proportion of individuals for whom aMCI represents the early stages of dementia, we examined the ability of each test to provide intra-group performance variation. The results indicate that as well as significant slowing in performance of the operations involved in TMT part B (but not part A), individuals with aMCI also experience significant slowing in RT compared to controls. The results also suggest that research-typical RT tests may be superior to the TMT in differentiating between cognitively healthy aging and aMCI at group level and in revealing the performance variability one would expect from an etiologically heterogeneous disorder such as aMCI.

Although there is some evidence that amnestic mild cognitive impairment (aMCI) can be characterized by significant deficits in visuospatial function, the cross-sectional design of the majority of these studies renders it impossible to determine whether such deficits occur in aMCI as a result of, or accompany, amnestic dysfunction per se or whether they are the result of disproportionately poorer performance in a sub-group of patients for whom aMCI represents prodromal dementia. Similarly, whether the absence of aMCI-related functional deficit stems from the masking of dementia-specific abnormality by the preserved performance of those with a different cause of aMCI cannot be ascertained. Here we report the outcome of a cross-sectional and 2.5-year longitudinal evaluation follow-up, computer-based study of visuospatial attention, specifically attentional disengagement and inhibition of return and the mean (RTSPEED) and intra-individual variability (IIVRT) of their component reaction times, in 45 patients with aMCI and 31 cognitively healthy older adults. Reduced inhibition of return (p = 0.01 and p = 0.037 in response to 400 and 800 ms cue to target interval conditions), slowed RTSPEED (p = 0.038 and p = 0.03 in response to 400 and 800 ms cue), and raised IIVRT at baseline testing (p = 0.003, p = 0.026, p = 0.013 in response to 200, 400 and 800 ms cue) were associated with the development of dementia within the 2.5-year follow-up period, whereas the performance of patients with aMCI who did not develop dementia did not differ significantly from that of the cognitively healthy controls. Attentional disengagement appeared insensitive to the presence of prodromal dementia or amnestic dysfunction per se. The results indicate that those patients for whom aMCI represents prodromal dementia may experience, in addition to amnestic dysfunction, a decline in the functional integrity of some fundamental aspects of visual information processing, an effect potentially capable of increasing disease burden and reducing quality of life.