Age-related hearing loss (ARHL) is a common problem for older adults, leading to communication difficulties, isolation, and cognitive decline. Recently, hearing loss has been identified as potentially the most modifiable risk factor for dementia. Listening in challenging situations, or when the auditory system is damaged, strains cortical resources, and this may change how the brain responds to cognitively demanding situations more generally. We review the effects of ARHL on brain areas involved in speech perception, from the auditory cortex, through attentional networks, to the motor system. We explore current perspectives on the possible causal relationship between hearing loss, neural reorganisation, and cognitive impairment. Through this synthesis we aim to inspire innovative research and novel interventions for alleviating hearing loss and cognitive decline.The Ageing Ear: Tired of Listening? ARHL, or presbycusis, is characterised by gradually developing high-frequency hearing loss, often accompanied by poor speech discrimination, and may begin to surface in the fourth decade of life [1]. The prevalence of ARHL increases with age, affecting N40% of people over 50 years old, rising to~71% of people over 70 years [2]. For most people this is a relatively unremarkable part of the ageing process (Box 1), but some individuals with ARHL experience effort and difficulties in understanding speech, hindering communication and socialisation [3]. Increased listening effort may lead older adults to avoid social interaction, exacerbating loneliness and depression, and reducing well-being [4]. Recent research further shows that hearing loss is associated with cognitive decline and dementia [5,6]. However, although there is reasonable evidence for hearing loss as a marker for risk of cognitive decline, it is not yet clear whether there is a causal effect of hearing loss on cognitive decline. Collating the most recent evidence on how ARHL affects the brain provides valuable information on the possible underlying mechanisms and causal relationships between hearing loss, neural changes, and dementia. This review discusses the physiology of ARHL, from the peripheral auditory system to the auditory cortex, and to global neural changes that accompany ARHL. We focus on the impact of these cortical changes on cognitive functioning during ageing, and explore the evidence for a possible causal relationship between ARHL-related changes in neural functioning and cognitive decline.The Peripheral and Subcortical Auditory Systems in Age-Related Hearing Loss ARHL is attributed to sensory, metabolic, or neural changes in the peripheral auditory system which affect hearing ability. Sensory ARHL is characterised by degeneration of outer and inner hair cells within the cochlea, of which the inner cells are responsible for the transduction of auditory signals. Atrophy originates in the basal end of the cochlea, and over time progresses to the apex. Basal atrophy manifests in the high-frequency hearing loss typical of sensory ARHL [7]. It has b...

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Motivation scientists employing physiological measures to gather information about motivation-related states are at risk of committing two fundamental errors: overstating the inferences that can be drawn from their physiological measures and circular reasoning. We critically discuss two complementary approaches, Cacioppo and colleagues' model of psychophysiological relations and construct validation theory, to highlight the conditions under which these errors are committed and provide guidance on how to avoid them. In particular, we demonstrate that the direct inference from changes in a physiological measure to changes in a motivation-related state requires the demonstration that the measure is not related to other relevant psychological states. We also point out that circular reasoning can be avoided by separating the definition of the motivation-related state from the hypotheses that are empirically tested.

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The World Health Organization (WHO) aims to improve our understanding of the factors that promote healthy cognitive ageing and combat dementia. Ageing theories that consider individual ageing trajectories are of paramount importance to meet the WHO’s aim. Both the revised Scaffolding Theory of Aging and Cognition (STAC-r) and Cognitive Reserve theory (CR) offer theoretical frameworks for the mechanisms of cognitive ageing and the positive influence of an engaged lifestyle. STAC-r additionally considers adverse factors, such as depression. The two theories explain different, though partly overlapping aspects of cognitive ageing. Currently, it is unclear where the theories agree and differ and what compensation mechanism of age-related cognitive decline might be better explained by either STAC-r, CR, or by both. This review provides an essential discussion of the similarities and differences between these prominent cognitive ageing theories, their implications for intervention methods and neurodegenerative disease, and significant shortcomings that have not yet been addressed. This review will direct researchers to common insights in the field and to intervention targets and testable hypotheses for future research. Future research should investigate the potential use of STAC-r in neurodegenerative diseases and provide clarity as to what combination of factors build CR, including their relative importance and when in life they are most effective.