A recent study from researchers at the University of Hong Kong found that people with subjective cognitive decline (SCD) — a self-reported worsening of memory that doubles dementia risk — show weaker brain responses to certain types of speech. The key factor is not just what is said, but how it is expressed.
The research
Matthew King-Hang Ma and colleagues (2025) recorded EEG from 60 cognitively normal older adults while they listened to speech varying in expressive style: scrambled (random syllables), descriptive (flat factual), dialogue (conversational), and exciting (animated). The researchers built encoding models to see how well three speech representations — acoustic, subsyllabic (e.g., syllables), and phonotactic (e.g., rules for sound sequences) — predicted ongoing brain signals.
Overall, models using subsyllabic linguistic features tracked brain activity better than acoustic ones. However, participants reporting more SCD symptoms showed weaker cortical tracking strength (CTS) for subsyllabic features — but not for acoustic ones. The effect was especially pronounced when listening to prosodically flat speech (scrambled and descriptive).
The authors conclude that measuring how the brain tracks higher-level linguistic features during monotonous speech could serve as a neural marker for early-stage cognitive decline.
Why it matters
SCD is considered a precursor to dementia, but it's often dismissed as just 'feeling forgetful.' This study provides a specific, objective brain signature that could help identify those at highest risk. The fact that the effect shows up during flat speech — not exciting dialogue — suggests that the brain's ability to compensate for boring prosody may be compromised early on.
For the average person, it highlights that how we process speech (not just memory) may reveal cognitive health.
What you can do
While this marker isn't available as a home test yet, you can challenge your brain by listening to audiobooks or podcasts in 'flat' formats (e.g., without music or dramatic narration) and trying to follow the content. Engaging with complex linguistic material keeps your neural speech tracking systems active.
Source: arXiv q-bio.NC
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