This is a Discovery Research Grant awarded to Dr Brian Allman at the University of Western Ontario, Canada in 2019. We’re co-funding this grant in partnership with Alzheimer’s Research UK.
Recent evidence shows there’s a link between dementia and hearing loss. Mild hearing loss doubles the risk of a person developing dementia, and the risk increases with the severity of hearing loss: moderate hearing loss increases the risk by three times and severe hearing loss by five times. Hearing loss can also be misdiagnosed as dementia or make the symptoms of dementia appear worse.
Little is understood about the link between dementia and hearing loss and the processes underlying both conditions. There’s evidence from studies carried out in animals that inflammation of nerve cells in the brain (‘neuroinflammation’) occurs with both exposure to loud noise (loud enough to cause hearing loss) and during the decline in cognitive abilities that occurs with aging. It’s therefore possible that neuroinflammation is a link between the 2 conditions, and that the neuroinflammation that causes hearing loss may also worsen cognitive decline, and potentially increase the chances of developing dementia.
The researchers have 2 fundamental goals.
First, they’ll study the brain changes that occur during noise-induced hearing loss that may speed up the learning and memory impairments that normally occur in old age.
Secondly, they will investigate how hearing loss may worsen these cognitive problems and brain changes in a way that is specific to Alzheimer’s disease.
The researchers will expose rats to loud noise when they’re young, and then, at given times throughout their lifespan, they’ll carry out a combination of:
- non-invasive brain imaging
- behavioural testing of learning and memory
- and microscopic analysis of brain structures and pathology.
By performing these procedures on the same rats, the team will be able to connect the changes seen in the brain imaging studies with the underlying pathology they find under the microscope. They’ll study both normal rats and those whose genetics have been modified so that they are susceptible to developing brain damage that is consistent with people suffering from Alzheimer’s disease.
This research will provide one of the first investigations into the biological processes that link hearing loss, age-related cognitive decline, brain inflammation and Alzheimer’s-related pathology.
Ultimately, this knowledge may lead to the development of treatments that can be used in people, such as drugs aimed at reducing the risk of dementia associated with hearing loss, which could have considerable future clinical implications for millions of people.