The Age-Related Central Auditory Processing Disorder: Silent Impairment of the Cognitive Ear

Abstract

Age-related hearing loss (ARHL), also called presbycusis, is a progressive disorder affecting hearing functions and among the elderly has been recognized as the third most frequent condition. Among ARHL components, the age-related central auditory processing disorder (CAPD) refers to changes in the auditory network, negatively impacting auditory perception and/or the speech communication performance. The relationship between auditory-perception and speech communication difficulties in age-related CAPD is difficult to establish, mainly because many older subjects have concomitant peripheral ARHL and age-related cognitive changes. In the last two decades, the association between cognitive impairment and ARHL has received great attention. Peripheral ARHL has recently been defined as the modifiable risk factor with the greatest impact on the development of dementia. Even if very few studies have analyzed the relationship between cognitive decline and age-related CAPD, a strong association was highlighted. Therefore, age-related CAPD could be a specific process related to neurodegeneration. Since these two disorders can be concomitant, drawing causal inferences is difficult. The assumption that ARHL, particularly age-related CAPD, may increase the risk of cognitive impairment in the elderly remains unchallenged. This review aims to summarize the evidence of associations between age-related CAPD and cognitive disorders and to define the diagnostic procedure of CAPD in the elderly. Finally, we highlight the importance of tailoring the rehabilitation strategy to this relationship. Future longitudinal studies with larger sample sizes and the use of adequate assessment tools that can disentangle cognitive dysfunction from sensory impairments are warranted.

Keywords: MCI; age-related hearing loss; central auditory processing disorder; cognitive function; dementia; lifestyle; rehabilitation; sensorial frailty.

FIGURE 1

Different pathophysiological pathways of the age-related central auditory processing disorder (CAPD). The figure illustrates the myriad deficits [i.e., dichotic processing (ipsilateral and contralateral), speech recognition in noise, and temporal speech processing involved in age-related CAPD]. Each of these disorders has a particular location along the auditory pathways, i.e., superior olivary complex and corpus callosum, medial olivary complex, and temporal lobe, respectively. Moreover, each of these auditory functions is associated with a cognitive process that is susceptible to the neurodegeneration. Specifically, executive and attentive functions are associated with speech in noise processing, dichotic ipsi and contralateral processing, which are highlighted in orange in the figure, while working memory and speech perception are associated with temporal speech processing which is displayed in pink in the figure.

FIGURE 2

Logical algorithm tree of possible interventions on the age-related CAPD in cognitively impaired older subjects.