Dementia is an auditory brain disorder

Abstract

AbstractBackgroundWhile impaired hearing has emerged as a major potentiating factor for dementia, the basis for this relationship has not been defined. Most studies have emphasised the role of peripheral hearing loss. However, we hear with our brains: natural listening places immense computational demands on neural circuitry, and the neural networks pre‐eminently targeted by major dementias are essential for decoding and responding appropriately to the auditory environment. Auditory brain dysfunction is therefore predicted both to contribute importantly to hearing impairment in Alzheimer’s and other dementias and to be integral to the expression of neurodegenerative pathologies. Here I present an overview of evidence that speaks to this hypothesis.MethodsIn a series of linked experiments, we have assessed aspects of auditory cognition – the processes whereby the brain perceives, interprets and acts upon sounds ‐ in patient cohorts with Alzheimer’s disease and major syndromes of frontotemporal dementia, relative to healthy older individuals. We designed novel psychoacoustic tests to assess aspects of auditory scene analysis (the ‘cocktail party effect’ and localisation of sounds in space), comprehension of acoustically degraded speech and the processing of semantic and emotional information in sound in cognitively impaired people. Neuroanatomical mechanisms were assessed using voxel‐based morphometry and functional MRI.ResultsAcross experiments, after taking peripheral hearing function and general cognitive performance into account, patients with Alzheimer’s disease and frontotemporal dementias showed characteristic ‘auditory phenotypes’ or profiles of auditory cognitive impairment. Alzheimer’s disease is associated with impaired auditory scene analysis, linked to atrophy and dysfunction of temporo‐parietal cortical regions in the core ‘default mode network’ targeted by Alzheimer pathology. Frontotemporal dementia syndromes produce distinct impairments of auditory feature analysis, sound recognition and emotional valuation.ConclusionsAuditory brain dysfunction plays a key role in everyday hearing impairment and reflects core pathophysiology in major dementias. These findings raise the exciting prospect that auditory cognitive measures might be used in the early diagnosis of dementia, in guiding novel hearing interventions and as dynamic markers of therapeutic response in the dawning era of disease modification.