Abstract
Hearing loss, presbycusis, is one of the most common sensory declines in the ageing population. Presbycusis is characterised by a deterioration in the processing of temporal sound features as well as a decline in speech perception, thus indicating a possible central component. With the aim to explore the central component of presbycusis, we studied the function of the auditory cortex by functional MRI in two groups of elderly subjects (>65 years) and compared the results with young subjects (<lt;30 years). The elderly group with expressed presbycusis (EP) differed from the elderly group with mild presbycusis (MP) in hearing thresholds measured by pure tone audiometry, presence and amplitudes of transient otoacoustic emissions (TEOAE) and distortion-product oto-acoustic emissions (DPOAE), as well as in speech-understanding under noisy conditions. Acoustically evoked activity (pink noise centered around 350 Hz, 700 Hz, 1.5 kHz, 3 kHz, 8 kHz), recorded by BOLD fMRI from an area centered on Heschl’s gyrus, was used to determine age-related changes at the level of the auditory cortex. The fMRI showed only minimal activation in response to the 8 kHz stimulation, despite the fact that all subjects heard the stimulus. Both elderly groups showed greater activation in response to acoustical stimuli in the temporal lobes in comparison with young subjects. In addition, activation in the right temporal lobe was more expressed than in the left temporal lobe in both elderly groups, whereas in the young control subjects (YC) leftward lateralization was present. No statistically significant differences in activation of the auditory cortex were found between the MP and EP groups. The greater extent of cortical activation in elderly subjects in comparison with young subjects, with an asymmetry towards the right side, may serve as a compensatory mechanism for the impaired processing of auditory information appearing as a consequence of ageing.
Highlights
Ageing affects the central nervous system in several ways, resulting in the atrophy of grey and white matter [1], changes in the levels of cortical metabolites and in functional deterioration leading to cognitive decline
Forty-eight subjects were examined in this study and were divided into 3 groups based on their age and hearing thresholds: 15 elderly subjects with a mild state of presbycusis (MP; 4 men and 11 women) between the ages of 65–72, 15 elderly subjects with expressed presbycusis (EP; 9 men and 6 women) between the ages of 64–79 and 18 young subjects (11 men and 7 women) between 22 and
The number of activated voxels decreased with increasing stimulation frequency in all groups, but the decrease was more prominent in both elderly groups with the most significant drop in EP
Summary
Ageing affects the central nervous system in several ways, resulting in the atrophy of grey and white matter [1], changes in the levels of cortical metabolites and in functional deterioration leading to cognitive decline. The latter is even more pronounced in the case of Alzheimer’s disease, mild cognitive impairment or dementia, which are more prevalent in the ageing population [2]. Individuals with the above-mentioned pathologies are more susceptible to develop age related hearing loss, presbycusis [3, 4]. In addition to increasing life expectancies, presbycusis is becoming an increasingly relevant social healthcare and economic problem [9]
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