Many older adults who scored below normal on a dementia screening test, but who had no noticeable communication problems, nonetheless had abnormal functioning in the brain stem and auditory cortex (regions of the brain that process speech), according to a new joint study by Baycrest Centre for Geriatric Care in Canada and the University of Memphis.
While these brain regions were previously thought to be more resilient to Alzheimer’s, the findings suggest that abnormalities in these areas may be new early signs of dementia risk.
The discovery shows changes occur early in the brain’s conversion of speech sound into understandable words. This finding could be the first sign of decline in brain function related to communication that presents itself before individuals become aware of any problems.
The study, published in the Journal of Neuroscience, focused on older adults with no known history of neurological or psychiatric illnesses with similar hearing acuity.
The scientists’ research technique of measuring electrical brain activity using an electroencephalogram (EEG) in these brain regions also predicted mild cognitive impairment (MCI), a condition that is likely to develop into Alzheimer’s, with 80 percent accuracy.
The brain activity within the brainstem of these older participants exhibited abnormally large speech sound processing within seven to 10 milliseconds of the signal hitting the ear, which could be a sign of greater communication problems in the future.
“This opens a new door in identifying biological markers for dementia since we might consider using the brain’s processing of speech sounds as a new way to detect the disease earlier,” said Dr. Claude Alain, the study’s senior author and senior scientist at Baycrest’s Rotman Research Institute (RRI) and professor at the University of Toronto’s psychology department.
“Losing the ability to communicate is devastating and this finding could lead to the development of targeted treatments or interventions to maintain this capability and slow progression of the disease.”
For the study, 23 older adults aged 52 to 86 were divided into two groups based on their results on a dementia screening test, the Montreal Cognitive Assessment (MoCA). The researchers measured brain activity in the brainstem while participants watched a video. They measured brain activity in the auditory cortex while participants were identifying vowel sounds. Statistical methods were used to combine both sets of brain activity to predict MCI.
“When we hear a sound, the normal aging brain keeps the sound in check during processing, but those with MCI have lost this inhibition and it was as if the flood gates were open since their neural response to the same sounds were over-exaggerated,” said Dr. Gavin Bidelman, first author on the study, a former RRI post-doctoral fellow and assistant professor at the University of Memphis.
“This functional biomarker could help identify people who should be monitored more closely for their risk of developing dementia.”
Next, the researchers want to find out whether those individuals who already have dementia or convert early from MCI to dementia also exhibit these same changes in brain activity when they hear speech.
With additional funds, researchers could explore developing a portable, reliable, and easy-to-use alternate diagnostic test for MCI that incorporates the body’s different senses.
“MCI is known to cause changes in different senses, such as vision or touch,” said Alain. “If we could incorporate these changes into a wireless EEG test, we could combine all this information and develop a better biomarker. One day, doctors could administer a short, 10-minute assessment and instantly provide results.”