Researchers here present epidemiological evidence for head injuries to leave permanent consequences that accelerate later cognitive decline. Speculatively, the mechanisms by which this might happen could include a increased lasting presence of senescent cells in injured tissue, raising local levels of inflammation. Certainly there is suggestive evidence for some forms of injury, including injuries to the brain, to leave a lasting mark in the form of raised inflammation in tissues. Senescent cells are frequently involved in inflammation-related mechanisms and conditions.
Head injuries did not appear to contribute to brain damage characteristic of Alzheimer's disease, but might make people more vulnerable to dementia symptoms, according to new findings. "Here we found compelling evidence that head injuries in early or mid-life can have a small but significant impact on brain health and thinking skills in the long term. It might be that a head injury makes the brain more vulnerable to, or accelerates, the normal brain ageing process."
The study involved 502 participants of the UK's longest-running cohort study, the MRC National Survey of Health and Development Cohort, which has been following participants since their birth in the same week in 1946. At age 53, they were asked 'Have you ever been knocked unconscious?' to assess whether they had ever suffered a substantial head injury; 21% of their sample had answered yes to this question. And then around age 70 (69-71), the study participants underwent brain scans (PET/MRI), and they took a suite of cognitive tests.
The participants had all completed standardised cognitive tests at age eight, so the researchers were able to compare their results at age 70 with expected results based on their childhood cognition and other factors such as educational attainment and socioeconomic status. The researchers found that 70-year-olds who had experienced a serious head injury more than 15 years earlier performed slightly worse than expected on cognitive tests for attention and quick thinking (a difference of two points, scoring 46 versus 48 on a 93-point scale). They also had smaller brain volumes (by 1%) and differences in brain microstructural integrity, in line with evidence from previous studies, which may explain the subtle cognitive differences.
The researchers did not find any differences in levels of the amyloid protein, implicated in Alzheimer's disease, or other signs of Alzheimer's-related damage. "It looks like head injuries can make our brains more vulnerable to the normal effects of ageing. We have not found evidence that a head injury would cause dementia, but it could exacerbate or accelerate some dementia symptoms."