A recent publication in the journal of Nature Medicine, reports on a newly devised ‘brain clock’ that can determine whether a person’s brain is ageing faster than their actual, chronological age. The clock indicated that brains age faster in countries with greater inequality.
Brain Network Dynamics
The global research team looked at the degree to which brain regions interact with one another. This functional connectivity typically declines with age. They measured the blood flow and activity in the brains of participants when they were at “rest”, using either functional magnetic resonance imaging (fMRI) or electroencephalography (EEG), respectively.
Brain Age Gaps
Using a type of Artificial Intelligence, the authors entered the measurements into two deep-learning models trained to predict brain age – one for the fMRI data and one for EEG data. The team then used this to calculate each person’s ‘brain-age gap’ – the difference between their chronological age and their brain age estimated from functional connectivity. A brain age gap of five years for example, would mean that your brain connectivity is around the same as that of someone five years older than you.
A Global Dataset
The study drew on datasets of 5,306 participants across 15 countries. fMRI data included 2,953 participants from Argentina, Chile, Colombia, Mexico, Peru, the United States of America, China, and Japan. EEG data involved 2,353 participants from Argentina, Brazil, Chile, Colombia, Cuba, Greece, Ireland, Italy, Turkey, and the United Kingdom. The sample included 3,509 participants with healthy brains, 828 participants with Alzheimer’s disease, 463 participants with frontotemporal dementia and 517 participants with mild cognitive impairment (typically a precursor to dementia).
Structural Inequality
Socio-economic inequality, exposure to air pollution and health disparities were linked to larger brain-age gaps, particularly in people from Latin America. The research also highlighted sex differences in brain ageing. Specifically, women living in countries with high gender inequality —again those in Latin America and the Caribbean — tended to have larger brain-age gaps than did men in those countries. The models also showed that people with Alzheimer’s or another type of dementia had larger brain-age gaps than did those with mild cognitive impairment or healthy brains.
What does this mean?
Functional connectivity is only one way to measure brain health. The EEG dataset used in the study lacked representation from dementia groups in the non-Latin American and Caribbean countries. However, quantifying brain ageing across such a large geographically diverse sample is an astonishing achievement. It reminds us that the way our brains age is not just about chronological years, it is also about where we live, what we do, our social class, and the level of pollution in our environment. The findings have potential implications for many countries wanting to invest in the brain health of its people, for example through tackling socioeconomic inequality and environmental pollution.