Detection of subtle differences in cognitive function

Cognitive screening in the elderly has received increased attention in recent years given the increasing prevalence of dementia as the average age of the population rises. Since treatments are likely to be more effective at the milder stages of cognitive decline, there is a need to develop reliable measures that can detect the onset of cognitive deficits as early as possible. The overall aim of this thesis was to use a new computerised test of cognitive function, the Subtle Cognitive Impairment Test (SCIT), to examine its sensitivity to subtle deficits in cognitive function, and its capacity to monitor changes in cognitive performance over time. Three separate studies were conducted to achieve this aim. The first study tested 96 community dwelling elders on the SCIT and the Mini-Mental State Examination (MMSE), the gold standard for dementia screening. SCIT performance was found to differentiate between MMSE scores that have previously been considered to be in the range that is appropriate for ‘cognitively normal’ individuals. Furthermore the pattern of impairment on the SCIT varied according to the subtests of the MMSE the participants made errors in. This correspondence raises the possibility that there may be different subtypes of subtle cognitive impairment within the ostensibly normal population of elderly. The second study tracked 50 of the elderly from the first study over a period of 12-17 months. Participants whose SCIT performance was weaker than others with a similar MMSE score were more likely to have lower MMSE scores a year later, while those whose SCIT performance was stronger were more likely to improve. Combining aspects of SCIT performance with the age of the individual successfully predicted future MMSE decline with 80% accuracy. The third study repeatedly measured the performance of undergraduate students during a period of mild alcohol intoxication. Comparisons were made against performance in the same individuals in an alcohol-free condition. Performance on the SCIT was found to be significantly impaired at Blood Alcohol Concentrations (BACs) below the legal limit for driving in Australia and most vi Western countries, and differences in performance were found between males and females. The SCIT was sensitive to both deficits and improvements in cognitive function during this short period of intoxication. The findings from this thesis indicate that the SCIT has utility in situations where it is necessary to detect low levels of cognitive impairment and also where repeated measurements need to be made in order to follow changes in cognitive performance over time.