The cognitive ear: the emerging role in the aging.

Hearing impairment is known as a major clinical risk factor for cognitive decline, with relevant clinical implications for dementia prevention, diagnosis, and treatment. However, the complex pathophysiological relation between hearing impairment and dementia remains to be fully defined. Consistently with the concept of an "hearing health trajectory," beginning at conception/birth and continuing throughout life in which environmental factors, such as noise, medicaments, and lifestyles (e.g., alcohol, smoking, diabetes, and weight gain), contribute to affect hearing. Several studies identified the exposure noise-induced hearing loss (NIHL) as a risk factor for sensory aging and cognitive decline processes. Although the association among age related hearing loss (ARHL), NIHL, and cognitive impairment has been clinically widely documented the molecular mechanisms underlying this association are not fully understood, and it is not known how these risk factors (sensory aging and noise) can interact, affecting brain functions. We recently found that early noise exposure in an established animal model of ARHL (C57BL/6 mice) accelerates the onset of age-related cochlear dysfunctions. While an animal model of Alzheimer's disease (AD), that is the 3 x Tg-AD mice we found that NIHL before that phenotype is manifested, caused persistent synaptic and morphological alterations in the auditory cortex and earlier hippocampal dysfunction, increased tau phosphorylation, neuroinflamma-tion, and redox imbalance, along with anticipated memory deficits compared to the expected time-course of the neurodegenerative phenotype. Furthermore, in the WT mice also HL, can accelerate ARHL onset inducing persistent synaptic alterations in both auditory cortex and hippocampus affecting memory performance and oxidative-inflammatory injury. Collectively, our experimental data confirm the existence of "cognitive ear" that can be early affected, thus midlife HL can be responsible for a hippocampal-dependent memory dysfunction. Considering that memory dysfunction is usually the first cognitive symptom of dementia (like AD) onset, from a translational point of view, our results support the hypothesis that associating auditory and memory screenings could represent a powerful non-invasive tool to potentially identify subjects with a high risk to develop dementia, allowing early diagnosis and treatment. [ABSTRACT FROM AUTHOR]