Deficits and compensation in healthy ageing, mild cognitive impairment and Alzheimer’s disease : a mismatch negativity study of visual, auditory and audiovisual processing

Research output: ThesisDoctoral Thesis

Abstract

An increasing ageing population presents the challenge of understanding how healthy ageing and dementia affect brain function. Improved understanding of healthy ageing can provide a baseline against which to examine Mild. - Cognitive Impairment (MCI) and Alzheimer's disease (AD) in which there is a great need for better characterisation and early diagnostic tools. Examining sensory processing can reveal how the ageing brain copes and reacts to changes in peripheral sensory deficits and can inform theories of cognitive ageing. Additionally sensory processing has largely been neglected in the examination of MCI and AD, and may provide further understanding of the early stages of the disease processes, unaffected by the educational and cultural confounds that can often hamper measures of higher level processing. This thesis explored sensory processing in healthy ageing, MCI and AD with two distinct aims: 1) to test and further inform cognitive theories of healthy ageing and 2) to identify changes in sensory processing due to MCI and AD that may be further developed as diagnostic markers. Electroencephalography was used to measure sensory processing across four paradigms designed to examine visual, auditory and audiovisual processing. Early sensory evoked potentials and the mismatch negativity response were measured in healthy younger and older adults, MC! patients and AD patients. -The results indicated that older adults experience modality specific changes in sensory processing, with patterns of a frontal lobe inhibitory deficit emerging in auditory processing, and cortical compensation to reduced peripheral input in visual processing. AD patients showed deficits in sensory association area processing that manifested as reduced audiovisual binding and reduced visual evoked potentials. MC! patients showed high intra and inter individual variability in visual processing and a broad attentional deficit in evoked potentials across both auditory and visual modalities. This thesis demonstrates that the healthily ageing brain adapts to changes in peripheral sensory processing in an adaptive, compensatory manner that is specific to the sensory modality examined. Both MCI and AD show specific changes in sensory processing that with future improvements in individual subject analyses provide considerable potential for improved early classification and diagnosis.
Original languageEnglish
QualificationPh.D.
Awarding Institution
  • University of Bristol
Award date1 Jan 2013
Publisher
Publication statusPublished - 2013

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