BRU and BRC supported researchers have demonstrated that dementias previously thought to be ‘language-led’, also extend to areas of the brain related to sound.
Primary progressive aphasias (PPA) are ‘language-led dementias’. Over the past ten years Professor Jason Warren, corresponding author on the paper in Neurobiology of Aging, and his collaborators have been investigating nonverbal auditory and other related symptoms of PPA, using cognitive neuropsychology and structural brain MRI.
Prof Warren said: “We have been struck for some time by the diverse nonverbal auditory symptoms that patients with PPA and their caregivers frequently volunteer. These include difficulties following sounds in background noise, problems identifying sounds in the environment and altered emotional and behavioural responses to sound.”
These symptoms are not part of standard diagnostic guidelines but substantially affect quality of life and more fundamentally, seemed to suggest a new way of thinking about these diseases beyond the conventional realms of speech and language.
This present study is one of the first in the world to apply activation functional MRI (fMRI) to capture the working brain in PPA. The study team looked at a large, very well defined, cohort of patients representing all major forms of PPA, in comparison to healthy, older people. They created a new set of stimuli based on varying specific auditory attributes of spoken syllables and played these sound stimuli to volunteers while they were lying quietly in the MRI scanner and recorded their brain activity changes in response to the sounds.
Prof Warren added: “All that the volunteers had to do during scanning was to listen to the sounds – there was no task to perform in the scanner. This is important since the stress of performing tasks that patients find difficult could otherwise alter the brain activity changes we were seeking to measure.”
The study team found that the three major PPA variant forms – nonfluent PPA, semantic PPA and logopenic PPA – each have characteristic, syndromic profiles of altered brain function when decoding fundamental kinds of information in sound. Nonfluent PPA has abnormal processing of rhythmic patterns; semantic PPA has abnormal prediction of how patterns will evolve in future; and logopenic PPA has abnormal discrimination of speech from other sounds.
Explaining the scientific impact of the study, Prof Warren said: “Scientifically, this work shows that the core problem in PPA goes much deeper than was previously suspected, to affect very fundamental modes of brain operation, specifically the way the cortex processes information in these dementias.”
The hope is that the work will generate interest in new diagnostic strategies and biomarkers of PPA and new ways to assess treatments in these patients.
