BY: SAMANTHA BARTLETT, DVM
A study published in the Journal of Veterinary Internal Medicine (JVIM) in August 2022 has shown a link between hearing loss in senior dogs and increased symptoms of canine cognitive dysfunction (CCD). It is known that hearing loss is a risk factor for dementia in aging humans. Study lead, Gilad Fefer at North Carolina State University, set out to determine if the same was true for older canines.
It has been suggested that the link between hearing and mental function is due to the fact that the interpretation of sound and a large amount of cognitive processing for short-term memory both occur in the temporal lobe. Loss of hearing results in associated cells of the brain being understimulated and eventually deteriorating affecting the function of the rest of this area of the brain. Age relating hearing loss in canines typically begins around 8 to 10 years of age. The greatest loss begin with high frequencies then middle frequencies of sound.
The study involve 39 dogs whose median age was 13 years old and otherwise healthy. Each dog was tested for hearing using the brainstem auditory evoked response (BAER) method, which measures the electrical response to sound in the cochlear nerve. Dogs without hearing loss could hear tones at 50 dB, the group with moderate hearing loss could hear tones at 70 dB and the severely impaired group could only hear tones at 90 dB or more.
Dog owners were asked to complete a questionnaire evaluating their dog’s quality of life including vitality and companionship. They were also asked to complete a second questionnaire evaluating symptoms of cognitive decline. Researchers found that vitality and companionship behaviors declined significantly with the deterioration of hearing ability.
OF the dogs with normal hearing, 61 percent were free of symptoms of CCD – 31 percent had mild symptoms and 5 percent showed moderate symptoms of decline. Of dogs with moderate hearing loss, 50 percent showed moderate signs of dementia. Notably, of dogs with severe hearing loss, none were free of CCD symptoms with half of the group exhibiting severe symptoms of CCD.
This study suggests that the same correlation between hearing and cognitive function exists between people and dogs. This opens the possibility that finding a way to correct age-related hearing loss in dogs, possibly through cochlear implants, can prolong mental health in these individuals.
The JVIM article can be accessed at https://onlinelibrary.wiley.com/doi/10.1111/jvim.16510.
