Neurocognitive and electrophysiological indices of cognitive performance in ageing

Abstract

Combining neuropsychological and electrophysiological methodologies this thesis investigates differential cognitive performance in ageing and attempts to identify neurocognitive and electrophysiological markers with the capacity to distinguish between age groups (young, old) and/or cognitive performance groups (old High performers, old Low performers). Chapter 1 introduces cognitive ageing, theoretical perspectives, markers of cognitive decline, and associated research issues. Chapter 2 describes the participant classification approach and behavioural testing methods, and presents results from neuropsychological assessment and experimental tasks. The older adults were assigned to sub-groups, and classified as High- or Low performers based on their memory performance relative to an estimate of their pre-morbid IQ. Significant age differences are evident across measures of executive function, memory and processing speed. In contrast, High performers are only distinguished from Low performers on measures of memory. Chapter 3 examines reaction time (RT) latency and intra-individual variability on tasks that assess cognitive and motor processing speed, attention, and memory. RT latency distinguishes age groups on processing speed and memory measures but not on a task that measures sustained attention. Variability measures distinguished groups on the basis of age and cognitive performance. The electroencephalogram (EEG) was used to assess cortical activity while participants rested and while they encoded and retrieved words during an experimental episodic memory task. Chapter 4 describes the EEG, Event-Related Potentials (ERPs) and the techniques employed for acquisition and analysis. Chapter 5 presents results from spectral analysis of the EEG and shows that resting alpha power distinguishes participants on the basis of age and cognitive performance. In Chapter 6 putative ERP modulations of familiarity, recollection, and post retrieval monitoring, are analysed. Significant age differences are reported for familiarity and recollection effects. In addition, Low performers demonstrate a different pattern of event-related neural activity associated with recognition than the High performers and the Young controls when ERP waveforms are analysed according to the type of encoding irrespective of response accuracy. A detailed analysis of the ERP activity recorded during the encoding phase of a novel experimental episodic memory task is presented in Chapter 7. Clear age differences are evident and during the task High performers demonstrate a pattern of neural activity that is qualitatively different from the pattern observed in the Young. In contrast, the Low performers engage in a similar, but attenuated, pattern as the Young. A general discussion of these findings is presented in Chapter 8.