A 90-year-old brain typically weighs 1,100 to 1,200 grams, and this is 100 or more grams less than the typical 40-year-old brain. Brain shrinkage mostly affects the prefrontal cortex and hippocampus, and the cerebral cortex, which is important for complex thought processes. Over time, the brain can also be affected by declining levels of neurotransmitters, changing hormones, deteriorating blood vessels, and impaired circulation of blood glucose. These brain changes can affect thinking, making it harder to recall words and names, focus on tasks, and process new information.
Physically, the brains of cognitive super agers seem to defy wear and tear better than the average brain. Researchers at Northwestern University’s Mesulam Center for Cognitive Neurology and Alzheimer’s Disease in Chicago have tentatively identified a “brain signature” for cognitive super agers, which they define as people age 80 years and older who have performance on memory tests comparable to people two to three decades younger. The researchers conducted magnetic resonance imaging (MRI) scans on 12 cognitive super agers, 10 cognitively normal peers, and 14 cognitively normal people in the 50- to 65-year age range. Comparisons revealed that the cingulate cortex, a brain region considered important for the integration of information related to memory, attention, cognitive control, and motivation was thicker in super agers than in their same-age peers and showed no atrophy compared with the same brain region of the middle agers. In fact, a specific region of the anterior cingulate cortex was significantly thicker in the brains of cognitive super agers than in middle agers’ brains.
In a separate study, the Northwestern researchers found that super agers’ brains contained a much higher density of a particular type of cell called von Economo neurons, which are linked to social intelligence and awareness. Their brains had more of these neurons even than the brains of younger adults.
At Massachusetts General Hospital, Boston, researchers are studying younger super agers — people between age 60 and 80 who have memory recall abilities similar to those of 18- to 32-year-olds. They’ve identified distinctive thicknesses in two neural networks that connect parts of the brain important to memory function. The thickness is nearly the same as in the brains of younger adults. The researchers also found that super agers have a bigger hippocampus than other adults their age.
Researchers with UC Irvine’s 90+ Study have identified a curious and counterintuitive feature of the super ager brain: sometimes it shows the pathologies that characterize Alzheimer’s disease and related dementias.
Researchers are exploring several theories to explain why some people’s cognitive abilities stay intact to the end of life. Perhaps they start out in life with larger, stronger brains. Or perhaps their brains somehow change to compensate for aging’s damaging effects. Another theory being pursued is whether their brains have stronger defenses against the assaults of aging.
A person’s environment may be a factor. Human and animal studies by NIA-supported scientists have contributed to the growing body of evidence that enriching experiences, such as advanced education and mind-challenging occupations, can help brains last longer.
Social factors also could play a role in healthy cognitive aging. In one of Northwestern University’s studies, investigators gave a 42-item questionnaire on psychological well-being to 31 cognitive super agers and 19 cognitively normal peers. The cognitive super agers reported more friends and family connections, a finding that builds on past research showing links between psychological well-being and lower risk of Alzheimer’s.