A fascinating study published in this month’s Cerebral Cortex reports that a gene known to massively increase the risk of Alzheimer’s disease in later life is associated, in young people, with better memory performance and more efficient use of the brain’s memory structures.
The research team, led by neuroscientist Christian Mondadori, looked at the genetics and memory performance of 340 volunteers, all in their early 20s.
The team were particularly interested in which version or allele of the apolipoprotein E (ApoE) gene each person had, because the ‘Epsilon 4′ allele raises the risk for Alzheimer’s disease in old age.
In fact, people with two ‘Epsilon 4′ alleles are virtually guaranteed to the brain disorder by the age of 80.
Each person took part in a word learning test that involved both short-term and long-term memory. This type of test is known to particularly rely on the function of the hippocampus, a key memory area which is known to decline in Alzheimer’s disease.
People who were carriers of the Epsilon 4 allele performed better in the long-term memory test, and no different for short-term memory.
The team decided to do more extensive memory tests while brain scanning 34 participants who were picked specifically to represent equal numbers of the three common genetic combinations.
These tests in the scanner involved learning faces and associations with professions over a number of trials and a target detection task that involved manipulating information in short-term memory (working memory).
There was no difference between the groups in terms of their accuracy on these tests, but people with the Epsilon 4 allele showed decreases in brain activity as time went on, suggesting they were using their brain more efficiently.
In contrast, people without the Epsilon 4 allele showed increases in brain activity, suggesting their brain was having to work harder to keep up.
A key question is why people who carry the Epsilon 4 allele would have a more efficient brain system for memory in early life but are more likely to have these same memory systems degrade in later life, as happens in Alzheimer’s disease.
As Alzheimer’s typically strikes after the time most people have children, the researchers suggest that the Epsilon 4 allele could confer an evolutionary advantage without adversely affecting chances of reproduction.
Some evidence that supports this idea has been found in previous studies where the ApoE Epsilon 4 allele has been associated with higher IQ scores, reduced heart activity under stress, and reduced chance of difficulties during pregnancy and post-birth problems.
Link to abstract of scientific study.