Auditory system dysfunction in Alzheimer disease and its prodromal states: A review

Abstract

Recent findings suggest that both peripheral and central auditory system dysfunction occur in the prodromal stages of Alzheimer Disease (AD), and therefore may represent early indicators of the disease. In addition, loss of auditory function itself leads to communication difficulties, social isolation and poor quality of life for both patients with AD and their caregivers. Developing a greater understanding of auditory dysfunction in early AD may shed light on the mechanisms of disease progression and carry diagnostic and therapeutic importance. Herein, we review the literature on hearing abilities in AD and its prodromal stages investigated through methods such as pure-tone audiometry, dichotic listening tasks, and evoked response potentials. We propose that screening for peripheral and central auditory dysfunction in at-risk populations is a low-cost and effective means to identify early AD pathology and provides an entry point for therapeutic interventions that enhance the quality of life of AD patients.

Keywords: Audiometry; Auditory cortex; Dichotic; Evoked potential; Mild cognitive impairment.

Fig 1

Left) Diagram of the human auditory system illustrating the presumed generators of auditory evoked potentials. Right) Representative images of the auditory brainstem response (bottom), thought to be generated from the auditory brainstem and midbrain, P50 response (middle), thought to be generated from auditory subcortical generators, demonstrating responses to initial (orange) and subsequent (purple) stimuli and cortically-based (top) auditory evoked potentials.

Fig. 2

ERPs in response to 1000 Hz tones (“non-targets”, presented with a probability of 0.8) across five groups: young controls, aged controls, MCI-stable (do not convert to AD at up to 5 year follow-up), MCI-convert (convert to AD at up to 5 year follow-up) and AD. A) ERP waveforms for all four groups and C) for MCI-stable versus MCI-convert. B, D, E) Plots of average P50 [B and D] and N100 [E] across the different groups (**p < 0.01). In [B], circle = MCI-single domain and square = MCI-multiple domain. Error bars = standard deviation. Reproduced with permission from Golob et al., 2007.