The effects of late-life depression on memory : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Clinical Psychology at Massey University, Manawatu, New Zealand

Abstract

Depression is a common mental health issue. It can result in a number of difficulties with cognitive functions such as memory. This is particularly pertinent for those experiencing late-life depression (those aged 65 years and older), as it can lead to a reduced quality of life. The relationship between depression, short-term memory, working memory, and prospective memory in the literature was explored, with a special emphasis on memory and late-life depression. In general, past research is somewhat mixed although tends towards depression having a negative impact on all the above types of memory. The impact of depression on short-term, working, and prospective memories was investigated in a group of younger adults aged 20-29 years (n = 50) and older adults aged 70-79 years (n = 50). A between groups design was used, with each participant completing measures of depression, short-term memory (recall list), working memory (letter-number sequencing and reading span tasks), and prospective memory (with both time-based and event-based tasks). As moderating factors of memory, processing speed and an estimate of IQ were measured. Anxiety and perceived stress were measured as moderating factors for depression. The results of the present study were mixed. There were small effects for Depression and Depression x Age interactions across some of the working memory and time-based prospective memory analyses. Interesting results were obtained when the moderators were investigated. Visual processing speed and IQ had some small to medium effects for Depression and Depression x Age interactions for recall, reading span, and time-based prospective memory, although these effects were not always in the anticipated direction. Similar variable patterns appeared when the impact of anxiety and stress on memory were analysed. The implications of these mixed results are that a review of the way the constructs of depression, anxiety and stress are defined and measured is necessary for ongoing research in this area. Tests of depression are variable and have correlations with each other that are only marginally higher than their correlations with anxiety and stress measures. Difficulties with construct measurement extend to tests of working memory, with low correlations between working memory tests. This indicates that these tests may not be measuring the same things, yet current research on depression and memory often compares findings across multiple depression scales and tests of memory. This may have led to the inconsistent findings in the literature and may continue to do so until the issues of construct definition and measurement are addressed.