A cognitive study of spontaneous speech and writing in patients with Alzheimer's disease
Although most neuropsychological studies have focused upon the memory breakdown suffered by Alzheimer's Disease (AD) patients, recent research suggests that language, especially semantics, is a promising area to identify deficits in AD. No specific language tests, however, have been developed to assess language in AD, and much research is flawed by the absence of longitudinal assessment, the inclusion of a complex task and a failure to differentiate patients in terms of severity. It is, therefore, extremely difficult to identify the impairments characteristic of each disease stage, and almost impossible to isolate those evident in the earliest stages. The main aim of this thesis was to develop a standardised instrument comprising a simple and complex component, which can assess the spontaneous speech and writing of AD patients over time and to document the longitudinal pattern of speech and writing deterioration suffered by such patients. Results from a series of experiments indicated that the task had high inter-rater, test-re-test and parallel forms reliability, was sensitive to the impairments suffered by the mildest of AD patients, whilst also being a valid measure of language impairments. A cross sectional and longitudinal assessment indicated that speech and writing follow a logical progression as AD advances, with initial breakdown in lexical processing and a subsequent breakdown in syntactic, phonological and visuo-special skills. Although a number of patients did show impairments in articulation and melodic line, the motoric aspects of speech remain relatively preserved. Despite the preservation of motor functions in speech, patterns demonstrate a pattern of peripheral dysgraphia that is characterised by a progressive shift in writing style, and problems forming and selecting letters. Although a complex task was necessary to identify such impairments in the early stages of AD, a simple one was sufficient to identify those in the latter stages. In contrast to the proposal that AD is simply a result of exaggerated ageing, qualitative and quantitative differences were evidence between healthy elderly individuals and the mildest of AD patients. Indeed it seems that the pattern of language impairments shown by AD patients, arise as a result of cortical degeneration, which is centred in the temporal and parietal lobes, areas which are involved in the phonological and semantic aspects of language production.