Abstract

Hearing-loss (HL) is prevalent in adults with mild cognitive impairment (MCI), a risk state for Alzheimer’s disease. Both MCI and HL are associated with alterations in brain connectivity. These connectivity alterations have been associated with cognitive impairment in both groups and progression to Alzheimer’s disease in individuals with MCI. This suggests that altered brain connectivity may be related to the cognitive decline and increased dementia risk in these two populations. Despite this, HL and cognitive impairment are rarely investigated together in the context of brain connectivity. Based on this, we characterized the relationship between two measures of hearing and brain connectivity in adults with MCI. All data are from the Comprehensive Assessment of Neurodegeneration and Dementia study of the Canadian Consortium on Neurodegeneration in Aging. Based on a pure-tone screening protocol participants were classified as having either normal hearing (NH, n=60, %female= 40%, age=74.5, education=15.19) or HL (n=35, %female=48%, age=70.07, education=16.5). Groups were matched on gender and did not differ in age/education/Montreal Cognitive Assessment scores. Speech reception-thresholds were used as a measure of supra-threshold hearing ability. Analyses tested whether default-mode network and Heschl’s gyrus connectivity differed as a function each hearing measure. In all analyses, age, education, reading acuity, and contrast sensitivity were included as covariates. In all analyses using speech-reception threshold as a variable, pure-tone HL was controlled for. Hearing loss was associated with widespread alterations in functional connectivity. Compared to participants with NH, those with pure-tone HL had decreased connectivity between the default-mode network and the bilateral caudate and right thalamus. Compared to individuals with NH, those with pure-tone HL had increased connectivity between right Heschl’s gyrus and the right insula, the right operculum, and within right Heschl’s gyrus itself. They also had decreased connectivity between right Heschl’s gyrus and three regions in the left frontal lobe. Poorer speech-reception threshold was also associated with decreased connectivity between right Heschl’s gyrus and three regions in the left frontal lobe. Finally, there was no relationship between either measure of hearing and the connectivity of left Heschl’s gyrus. These results show that in individuals with MCI HL is associated with altered functional connectivity in regions responsible for sensory and higher order cognitive processing. This suggests that the increased risk for cognitive decline and dementia seen in individuals with HL may be due to alterations in functional connectivity reducing the brains’ ability to compensate for aging and Alzheimer’s disease related brain pathology.