Understanding speech in noise is one of the main communication difficulties of aging, and it often shows up before any obvious hearing loss. Close to this work sit studies of brain age maps, the link between white matter and cognitive functions, and MRI tractography of nerve fibers. However, most neighboring studies look at either cognitive or auditory changes alone, whereas this study directly ties the microstructure of auditory pathways, cognitive status, and behavioral measures of speech intelligibility in noise in the same people.
The study used data from the Human Connectome Project-Aging: 446 participants aged 45-90 underwent diffusion MRI, structural MRI, the MOCA cognitive test, and the WIN test of word recognition in noise. Deterministic tractography was used to isolate the arcuate fasciculus and the auditory pathways from the brainstem to the cortex, and their density (quantitative anisotropy) was measured. Volumes of the midbrain and Heschl's gyrus were obtained through automatic FreeSurfer segmentation. Statistical analysis was done with linear mixed models controlling for sex, age, handedness, and intracranial volume.
Age-related worsening of speech intelligibility in noise was significantly steeper in participants with low MOCA scores: by age 80 the difference reached about 5 dB. The turning point in cognitive decline appeared after age 65. Tractography revealed an opposite asymmetry: the density of brainstem auditory pathways was higher on the right, while that of the arcuate fasciculus was higher on the left. Only in the right hemisphere was an interaction found between age and cognitive status: in people with low MOCA, the density of the right arcuate fasciculus dropped more steeply with age and predicted better WIN scores. The volume of Heschl's gyrus decreased with age and correlated with speech intelligibility in noise, and this link was stronger in people with low MOCA.
The work stands out from its neighbors by tying together cognitive status, the microstructure of specific auditory pathways, and a behavioral test of speech intelligibility in noise in a large sample. This is the first study to show that early cognitive impairment accelerates the degradation specifically of the right arcuate fasciculus, and that its preservation supports speech perception in noise in cognitively vulnerable older adults. The results bolster models in which auditory and cognitive changes in aging reinforce each other.
The topic could move toward longitudinal studies that track how changes in auditory pathways precede a clinical diagnosis of dementia. Another promising direction is comparing structural data with functional brain activity during speech perception in noise. Of particular interest is testing whether hearing training or hearing aids can slow the degradation of the right arcuate fasciculus.
The results could influence early diagnosis of cognitive impairment through hearing tests and the development of interventions aimed at preserving auditory pathways.
Conduct longitudinal follow-up of participants with repeated measurements of hearing, cognitive status, and MRI. Test whether baseline measures of the right arcuate fasciculus predict future decline in cognitive functions.
The work addresses the unresolved question of whether auditory and cognitive impairments in aging are independent processes or share a common neurobiological basis. The data support the common-substrate hypothesis, but they do not rule out a cascading effect of auditory deprivation on cognition.
The density of white matter in the brainstem auditory pathways turned out to be higher in the right hemisphere, while in the arcuate fasciculus it was higher in the left. Such mirror asymmetry within a single sensory system had not been described before.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.