Spatial memory deficits in mild cognitive impairment : a virtual reality study of hippocampal and entorhinal functioning

This thesis explores the topic of Alzheimer’s disease (AD) and the earlier clinical state of mild cognitive impairment (MCI), with a particular focus on early identification and therapeutic intervention. The first part comprises a systematic review of the literature base examining the efficacy of transcranial direct current stimulation (tDCS; a form of non-invasive brain stimulation) in the treatment of MCI and AD. Specifically, this review focuses on the efficacy of tDCS for improving cognitive outcomes in MCI and AD patient groups. A database search identified fourteen studies that examined the relationship between tDCS and cognitive outcomes in these patient populations. The findings of these studies were summarised separately for MCI and AD patient groups. Results in both patient groups were found to be tentatively positive, however minimal research was carried out with MCI patient groups. Further, the heterogeneity of the identified research designs limited firm conclusions as to the factors associated with efficacy. Results are considered in tandem with an assessment of methodological quality. Consideration is given to the clinical implications of these findings, as well the areas that would benefit from further exploration in future research. In the second part of this thesis, an empirical paper is presented that examines the utility of a novel spatial memory task in the identification of early AD symptomatology. A virtual reality (VR) object-location memory task (OLT) was used to assess aspects of spatial memory that are underpinned by brain regions known to be affected in the earliest stages of AD: the hippocampus and entorhinal cortex (EC). In order to assess the utility of this task in a proof-of-concept study, the OLT was administered to patients diagnosed with amnestic MCI (aMCI), a diagnosis that represents a high-risk for conversion to AD, and healthy control participants. Alongside the OLT, a comparator battery of neuropsychological tests and a flat-screen measure of hippocampal function were administered as an index of the construct validity of the task. Results showed that there were significant group differences in performance on the OLT, and that task performance was able to predict group membership (aMCI or control) with a high degree of accuracy. Further, OLT performance was shown to be correlated with comparator measures of cognitive function. These results were interpreted as evidence for the utility of the OLT as a diagnostic measure. The implications of these findings were discussed in terms of the brain regions that the OLT may recruit, as well as the limitations of this study and how these might be addressed in future research. The third and final part of this thesis is a critical appraisal of the research process. This offers a reflective exploration of the experiential components of the OLT and how these might compare to more traditional measures of neuropsychological assessment. The emotional challenges associated with neuropsychological assessment are discussed, making use of quotes from the author and prominent AD spokesperson, Terry Pratchett. This section also includes reflections from the researcher on the process of carrying out this research, and the learning that took place as a result.