Auditory encoding of natural speech at subcortical and cortical levels is not indicative of cognitive decline.

Abstract

More and more patients worldwide are diagnosed with dementia, which emphasizes the urgent need for early detection markers. In this study, we built on the auditory hypersensitivity theory of a previous study-which postulated that responses to auditory input in the subcortex as well as cortex are enhanced in cognitive decline-, and examined auditory encoding of natural continuous speech at both neural levels for its indicative potential for cognitive decline. We recruited study participants aged 60 years and older, who were divided into two groups based on the Montreal Cognitive Assessment, one group with low scores (n = 19, participants with signs of cognitive decline), and a control group (n = 25). Participants completed an audiometric assessment and then we recorded their electroencephalography while they listened to an audiobook and click sounds. We derived Temporal Response Functions and evoked potentials from the data and examined response amplitudes for their potential to predict cognitive decline, controlling for age and hearing loss. Contrary to our expectations, no evidence of auditory hypersensitivity was observed in participants with signs of cognitive decline; response amplitudes were comparable in both cognitive groups. Moreover, the combination of response amplitudes showed no predictive value for cognitive decline. These results challenge the proposed hypothesis and emphasize the need for further research to identify reliable auditory markers for the early detection of cognitive decline.Significance statement Research on cognitive decline needs more studies uncovering markers for subtle neural changes in the pre-dementia stage. Neural markers for auditory processing have a potential that has not been widely explored in studies. Here, for the first time, we used natural, continuously spoken language to examine neural processing in two groups of older adults with and without cognitive decline. We quantified how well the brain tracks speech not only at the cortical but also at the subcortical level. In contrast to previous research suggesting that subcortical and cortical auditory responses are enhanced in cognitive decline, we found no group differences. We believe that this study represents an important contribution to the search for markers of cognitive health in old age.