The results, published Thursday in the journal Neurology, suggest a potential link between a history of head trauma and later cognitive decline.
Researchers at the Mayo Clinic in Rochester, Minn., enlisted 589 elderly residents of surrounding Olmsted County, beginning in 2004, and administered a battery of cognitive and memory tests, along with brain scans that reveal both structure and metabolic function.
Tests showed 448 of the subjects, aged 70 to 89, had no memory or cognitive problems, while 141 had mild cognitive impairment. A roughly equal proportion of each group reported at least one concussion that involved memory loss, unconsciousness or medical attention. The median age for that concussion event was 21 for men and 32 for women.
Only the brains of those with cognitive impairment showed higher levels of amyloids, a kind of fibrous protein, according to the study.
Researchers suggested that higher amyloid levels within the cognitively impaired group could be a response to a higher level of damage to the myelin coating of the axons of neurons – the brain’s white matter.
Amyloid buildup has been associated with neurological disorders, particularly Alzheimer’s disease. But studies linking head trauma to Alzheimer’s have shown somewhat conflicting results.
Although head trauma correlated with higher amyloid levels among those with mild cognitive decline, it did not correlate with a measurable difference in the volume of their hippocampus, a brain region related to memory, or with lower brain tissue metabolism, the study found.
Could higher amyloid buildup have led to the mild cognitive impairment, then? If so, researchers would expect to see a difference in test scores between those with concussion and those without a head trauma history. No such differences emerged within either the normal or impaired group. (In the cognitively normal group, in fact, those with a concussion history scored slightly higher than those without.)
Results also appeared to rule out differences related to time lapsed from the reported concussion – subjects experienced their concussions around the same age.
The study’s age range, 70 to 89, also could have excluded those who experienced early onset Alzheimer’s disease, including some who had serious head trauma. Some studies have associated head trauma with earlier manifestation of the disease symptoms.