Crossmodal plasticity effects of hearing loss and ageing in the human auditory cortex

Crossmodal plasticity refers to the phenomenon by which typical sensory areas respond to stimulation in other sensory modalities when their main input is absent or reduced. In this study, we examined the effect of age-related hearing loss (ARHL) on crossmodal plasticity in auditory brain regions. ARHL is prevalent in a large proportion of older adults, and it is associated with an increased risk of cognitive decline and dementia. Understanding how the brain adapts to ARHL is essential in aiding the development of adequate therapies and interventions for a phenomenon experienced by most adults aged 65 and over. Previous research in congenitally deaf adults has shown that crossmodal plasticity effects are stronger for conditions that require higher executive demands. We conducted an fMRI experiment in older adults to determine whether crossmodal recruitment of auditory cortical regions during higher executive demands also occurs following ARHL. In the MRI scanner, participants with and without ARHL completed a visual task-switching paradigm and a visual working memory task, each comprising high and low executive-demand conditions. Results from both groups of participants showed that the high-demand conditions reliably activated canonical frontoparietal regions involved in executive function and cognitive control. Crucially, we also observed significant recruitment of auditory regions during these visual tasks, particularly under the higher executive demands condition of the task-switching paradigm. Crossmodal activations in auditory areas occurred in both groups, with no significant effects of hearing level or age. These findings indicate that auditory regions are involved in high executive demand visual processing, and that crossmodal plasticity effects are not restricted to early sensitive periods. We propose that reduced auditory input and age-related changes in cortical processing jointly contribute to the reorganisation of the auditory cortex in later life. Understanding these mechanisms is critical for clarifying the neural consequences of ARHL and their impact on cognitive decline.