Prospective and retrospective memory in normal and pathological aging

This thesis aims to explore how prospective and retrospective memory are affected by health in old age. In this regard, we have focused on dementia disorders, depressive symptomatology, and thyroid functions. Prospective memory involves remembering to perform actions, such as paying bills or taking one’s medication. Retrospective memory involves remembering previous events or previously learned information, such as the content of a book. The memory process can be divided into three stages: encoding (forming new memories), storage (consolidation of information), and retrieval (remembering what we have previously encoded). In Study I, three groups were included: persons with Alzheimer’s disease, persons with vascular dementia, and healthy control persons. The groups were compared on prospective and retrospective memory tasks. The two dementia groups were impaired compared to controls on both prospective and retrospective memory, and the impairment was evident for all stages of the memory process (i.e., encoding, storage and retrieval). However, there were no differences between the two dementia groups regarding the extent or pattern of memory deficits. Study II examined how prospective and retrospective memory were affected during the so called preclinical phase of Alzheimer’s disease (i.e., before the disorder had progressed so much that it could be diagnosed). Both prospective and retrospective memory was impaired three years prior to diagnosis. In addition, the results showed that more people at risk of developing Alzheimer’s disease could be identified when the combined results from the two memory tasks were taken into account, compared to using only one task at the time. The unique contributions of both memory measures indicate that they are, at least in part, separable entities. When studying retrospective memory in more detail, we found that the impairment in preclinical Alzheimer’s disease was present across all three memory stages. Study III examined how depressive symptoms affected prospective and retrospective memory. Depressive symptoms refers to a continuum, ranging from states (such as mild dysphoria) that are common also among healthy persons to severe depressive disorders. The results showed that retrospective memory was negatively affected by depressive symptoms. The effect was evident for storage and retrieval, whereas there was a non-significant trend in the same direction for encoding. Prospective memory, however, was unaffected by depressive symptoms. If these results are valid, this can help us separate persons with depression from persons with early stage dementia, which in many cases is difficult. Study IV examined the effect of thyroid functioning on prospective memory. Thyroid function was measured through serum levels of two hormones: thyroid stimulating hormone (TSH) and thyroxine (T4). All participants were free from thyroid disorders. In spite of this, the results revealed that persons with higher TSH levels performed better on the prospective memory task. T4 levels were not related to memory performance. Previous research has shown a corresponding association between TSH and retrospective memory. The conclusion is that thyroid functioning has an impact on cognition, even in the absence of overt disease. To summarize, both prospective and retrospective memory are sensitive cognitive abilities, easily affected by disorders and other factors related to health. There are, however, some differences with regard to when, and how, these two forms of memory are affected. It is important to investigate this issue further, in order to gain a deeper understanding of the cognitive challenges that persons with different disorders or symptoms are facing. This can, in turn, lead to the development of new cognitive aids. In addition, cognitive psychology research can in some cases help us make faster and more accurate diagnoses.