Using fMRI to investigate speech-stream segregation and auditory attention in healthy adults and patients with memory complaints

Poor memory for recent conversations is the commonest presenting symptom in patients attending a cognitive neurology clinic. They also frequently have greater difficulty following and remembering conversations in the presence of background noise and/or unattended speech. While the ability to participate in and recall conversations depends on several cognitive functions (language-processing, attention, episodic and working memory), without the ability to perform auditory scene analysis, and more specifically speech-stream segregation, recall of verbal information will be impaired as a consequence of poor initial registration, over and above impaired encoding and subsequent retrieval. This thesis investigated auditory attention and speech-stream segregation in healthy participants (‘controls’) and patients presenting with ‘poor memory’, particularly a complaint of difficulty remembering recent verbal information. Although this resulted in the recruitment of many patients with possible or probable Alzheimer’s disease, it also included patients with mild cognitive impairment (MCI) of uncertain aetiology and a few with depression. Functional MRI data revealed brain activity involved in attention, working memory and speech-stream segregation as participants attended to a speaker in the absence and presence of background speech. The study on controls demonstrated that the right anterior insula, adjacent frontal operculum, left planum temporale and precuneus were more active when the attended speaker was partially masked by unattended speech. Analyses also revealed a central role for a right hemisphere system for successful attentive listening, a system that was not modulated by administration of a central cholinesterase inhibitor. Therefore, this study identified non-auditory higher-order regions in speech-stream segregation, and the demands on a right hemisphere system during attentive listening. Administration of a central cholinesterase inhibitor did not identify any benefit in the present patient group. However, my research has identified systems that might be therapeutic targets when attempting to modulate auditory attention and speech-stream segregation in patients with neurodegenerative disease.Open Acces