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    Electrophysiological and Behavioural Markers of Associative Source Memory Decline in Normal Ageing

    Brady, Noeleen M. (2013) Electrophysiological and Behavioural Markers of Associative Source Memory Decline in Normal Ageing. PhD thesis, National University of Ireland Maynooth.

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    Memory is the ability to encode and subsequently recall information (Brickman & Stern, 2009) and source memory refers to the ability to recall the source of the information, including all contextual aspects related to an event (Glisky & Kong, 2008; M. Johnson, Hashtroudi, & Lindsay, 1993). The ageing process shows a progressive decline in memory (Cabeza, Anderson, Locantore, & Mcintosh, 2002) which is thought to be related to atrophy in regions of the brain which are essential for memory (Pasquier, 1999). Source memory is particularly sensitive to cognitive ageing and is one of the first types of memory to show impairment (Jennings & Jacoby, 1997; Siedlecki, Salthouse, & Berish, 2005). In the current thesis different aspects of memory were measured to determine the extent of memory decline in ageing using associative, episodic and particularly source memory tasks. Both behavioural and electrophysiological methods were used to investigate cognitive changes in performance due to the ageing process between young and older adults along with an intervention at the time of acquisition to determine if source memory recall can be enhanced in older adults. In Chapter 3 memory retrieval was examined between young (18-30 years, n=27) and older (55-70 years, n=25) adults at three computer-based tasks, indexing source memory (an Opposition task), associative memory (a Visual Paired-Associates task) and episodic memory (a False Memory paradigm). Young and older adults were matched on estimated scores of IQ, short-term memory and self-ratings of their own memory. The results indicated that older adults have poorer accuracy and slower response times on memory tasks of associative and source memory, with the latter showing particularly large decrements due to ageing. Source deficits were clear on the Opposition task but context had little effect on accuracy on the VPAc task, while few differences were evident on the False Memory paradigm; therefore appears that memory for temporal context (i.e. the timing of an event) suffers more impairment in ageing. These results suggest that aspects of memory binding may be among the first memory processes to suffer a decline in healthy ageing. Chapter 4 examined young (18-30 years, n = 14) and older (50-75 years, n = 14) adults’ differences in recorded EEG for three computer-based memory tasks which assess source, episodic/associative and false memory. Reduced scalp electrical activity was observed in older adults on the source memory task coupled with a poorer behavioural performance. Reduced activity in older adults was also evident for mistaken lures and the correct identification of lures in the false memory task, but no behavioural differences were evident. For successful trials in associative memory tasks, increased activity was present in older adults while behavioural performance was either equal to or poorer than that of young adults. These data are mostly consistent with the idea that young adults show larger mean ERP amplitudes than older adults, suggesting a reduction in cognitive functioning in older adults which may have resulted in reduced memory accuracy capacity. In Chapter 5 data is reported from young (18-30, n = 15) and older (55+, n = 15) adults during behavioural measures of source memory and the associated electrophysiology. Participants completed the Opposition task and a Where-Who-What task. Results generally indicated that older adults displayed poorer behavioural performance and reduced amplitude P1 and P3 components on both tasks in comparison to young adults, which may reflect enhanced perceptual ability (linked to the P1) and recognition of the source of information (linked to the P3) in young adults compared to older. However, the electrophysiology predominantly showed enlarged waveform components in older participants at approximately 200ms for source memory tasks, and revealed more anterior positive scalp activity in the older compared to posterior topographies in the young which may indicate an automatic compensatory function in older adults. These patterns may reflect the recruitment of additional cortical areas acting in a compensatory manner to alleviate the age-related impairment in source memory tasks. An intervention with two source memory tasks was employed in Chapter 6. Three groups of adults, young control (18-30 years, n = 20), older control (55+ years, n = 20) and older intervention (55+ years, n = 20), took part in the experiment. Both control groups completed two computer-based source memory tasks without the use of an intervention, while the older intervention group used a strategy at the time of acquisition for both source memory tasks under two methods: firstly, sentence generation to enhance semantic binding; and secondly, story generation to increase contextual binding. Results indicate that the use of an intervention allowed for enhanced source memory recall in older adults compared to both control groups. In addition, the interventions led to faster response times compared to the older control group but not the young control group. It is concluded that while an intervention can alleviate the age-related deterioration of source memory accuracy, it does not entirely counteract the impairment in speed of processing typically seen in older adults. The behavioural results of this series of experiments indicate that source memory is negatively affected by the ageing process and that accuracy on source memory tasks is more affected than tasks involving associative and episodic memory. This supports previous findings indicating that memory for source is one of the first to decline with ageing. However, despite this discrepancy in source memory, an intervention strategy at the time of acquisition can lead to enhanced source memory recall in older adults compared to older and younger control adults. The electrophysiology may suggest that older adults have a decline in the perceptual processing of the source of information compared to young adults which may be reflected by the poorer behavioural performance on memory tasks. Furthermore older adults may attempt to compensate for these reductions in perceptual processing, as reflected by enlarged components at approximately 200ms. However, this compensation does not appear to be fully effective as the older adults retain poorer accuracies on source memory tasks. Additionally, the electrophysiology indicates further compensation as positive-going activity appears to occur more anteriorly in older adults which may reflect compensation for dysfunction in regions of the brain responsible for perceptual processing. These results provide additional support for two models of cognitive ageing, the Compensatory Related Utilisation of Neural Circuits Hypothesis (CRUNCH; Reuter-Lorenz & Cappell, 2008) and Posterior Anterior Shift in Ageing (PASA) models (S. W. Davis, Dennis, Daselaar, Fleck, & Cabeza, 2008).

    Item Type: Thesis (PhD)
    Keywords: Electrophysiological; Behavioural; Markers; Associative Source Memory Decline; Normal Ageing;
    Academic Unit: Faculty of Science and Engineering > Psychology
    Item ID: 7748
    Depositing User: IR eTheses
    Date Deposited: 13 Jan 2017 10:46
      Use Licence: This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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