Brain cost-efficiency linked to family genes

How well our brain functions is largely based on our family’s genetic makeup, according to a new study which provides the first evidence of a genetic effect on how ‘cost-efficient’ our brain network wiring is. Becky Crew reports.

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SYDNEY: How well our brain functions is largely based on our family’s genetic makeup, according to a new study which provides the first evidence of a genetic effect on how ‘cost-efficient’ our brain network wiring is.

The study, led by Australian researchers, was published in The Journal of Neuroscience and could shed light on why some people are better able to perform certain tasks than others and the genetic basis of mental illnesses and neurological diseases.

“Some brains are wired better than others, and 60% of the differences can be explained by genetic factors,” said lead author Alex Fornito from the Melbourne Neuropsychiatry Centre at the University of Melbourne. “The novelty is that we now have new methods to identify different aspects of brain network organisation. Previously it was very difficult to try and map these connections.”

More bang for your buck

Cost efficiency involves a balance between two competing priorities. Communication efficiency increases with the number of connections added, but the more connections, the more costly it is in terms of energy to run them.

“The brain tries to maximise its bang-for-buck by striking a balance between making more connections to promote efficient communication and minimising the ‘cost’ or amount of wiring required to make these connections,” said Fornito. “Our findings indicate that this balance, called ‘cost-efficiency’, has a strong genetic basis.”

According to Fornito, only recently have researchers started to look at the role of cost efficient communication in the brain. “We did expect that balancing these priorities would be important throughout evolution, and that evolution would favour a brain that makes the most of its available resources. We therefore reasoned that this balance should be encoded in our genes,” he said.

Strongest effects in prefrontal cortex

The research team, which included scientists at the Universities of Queensland and Cambridge, UK, compared the brain scans of 38 identical and 26 non-identical twins. Using new techniques, they were able to construct detailed maps of each person’s brain network and measured the cost-efficiency of network connections for the entire brain, as well as for specific brain regions.

“While we observed strong genetic effects on cost-efficiency of the entire brain, we also found that specific parts of the brain varied considerably in the degree to which their wiring was under genetic control.” said Fornito.

“We found some of the strongest effects in the prefrontal cortex, where up to 80% of the differences between people were attributable to genes. The prefrontal cortex plays a vital role in planning, strategic thinking, decision-making and memory.”

Uncovering genes linked to mental illness

Previous work has shown that people with more efficient brain connections score higher on tests of intelligence, and that brain network cost-efficiency is reduced in people with schizophrenia, particularly in the prefrontal cortex.

“The main thing that we’re interested in is links with mental illness. We know that the wiring of the prefrontal cortex is altered in people with schizophrenia. Our findings point to a potential genetic basis for these brain changes.” said Fornito.

“Although genes play a major role in brain function, the environment and other factors contribute to when things go wrong in cases of mental illness and other brain disorders,” he added.

“Ultimately, this research may help us uncover which specific genes are important in explaining differences in cognitive abilities, risk for mental illness and neurological diseases such as Alzheimer’s disease, leading to new gene-based therapies for these disorders.”

Figuring out more concrete models

“The paper represents an interesting and ingenious attempt to identify basic principles according to which the cerebral cortex is built up and wired,” said Vladamir Balcar from the School of Medical Sciences at the University of Sydney.

“I would like to see a prediction, based on the model, of something more concrete, related more directly to cortical structure. There would be considerable hurdles though. Most neuroanatomical techniques visualise only a small fraction of neurons and their possible connections and others visualise all the neurons but only small parts of them and no connections,” said Balcar.

“This implies that there might be neurons and connections not yet discovered and explains why our knowledge of cortical, anatomy is so horribly incomplete,” he added.

“Some laboratories decided they have enough and started to use specially modified electron microscopy to visualise all neurons and connections but this is producing so much data that if we wanted to apply it to larger regions of the cerebral cortex it would break not only our computers but also our research budgets.”

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