Traits like IQ, memory, and the tendency to use drugs are related to the number of brain connections we have, according to a new study.
The researchers found that people with more traits the researchers classified as "positive," like high IQ, tended to have a greater number of brain connections than people with more traits the researchers classified as "negative," like high drug use.
But some say we should be cautious in how we interpret the findings.
It's impossible to know whether weaker brain connectivity is the cause or effect of negative traits, Marcus Raichle, a neuroscientist at Washington University in St. Louis, Missouri, told Nature News.
The findings are the first results of a massive effort to map the connections between cells in the brains of more than 1,000 living people, known as the Human Connectome Project.
Launched in 2010 at a cost of $40 million, the five-year project aims to map all the connections within a healthy human brain and make the data available to scientists studying brain disorders.
University of Oxford biomedical engineer Stephen Smith and his colleagues studied 461 people enrolled in the Human Connectome Project. The volunteers had their brains scanned in a functional MRI machine, which measures blood flow to active parts of the brain.
The patterns they observed showed where parts of the brain were active and engaged, or "connected," at the same time.
The researchers compared these scans with characteristics like income, education level, and drug use, as well as cognitive measures like IQ and memory. They arranged the traits on a spectrum, with things like high IQ and more education on the "positive" end and things like low IQ and high drug use on the "negative" end.
The more "positive" traits people had, the more brain connections they found, and vice versa.
But the brain-wiring patterns linked to general intelligence were not the same as those for other kinds of intelligence, such as hand-eye coordination, some researchers noted. This suggests maybe we should reconsider what IQ tests actually measure, especially since many scientists think it's not the most useful measure of intelligence.
Interestingly, people who had recently used marijuana tended to be on the more negative end of the brain connectivity spectrum, the researchers said. But the jury's still out on how marijuana affects the brain.
The specific brain areas that contributed most to the findings were part of a circuit called the default-mode network, which is active when a person is focusing on internal thoughts instead of the outside world.
Scientists still debate exactly what this brain circuitry does, but previous research has linked it to several higher-level brain functions.
Other research has suggested that people with large groups of friends and good social skills have more connected brains.
And this is only the beginning of human connectome studies.
The Human Connectome Project is now looking at genetic data from people in the study, including many pairs of identical and fraternal twins, to see how genetic and environmental influences are related to brain connectivity.
Meanwhile, other groups are studying the brain connections of aging adults and developing babies.
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