'Selfish brain' wins out when competing with muscle power, study finds

October 20, 2017, University of Cambridge
Lead researcher Dr Danny Longman rowing with the Cambridge University Boat Club. This is an example of the type and standard of the sample population used in the study. Credit: Danny Longman

Human brains are expensive - metabolically speaking. It takes lot of energy to run our sophisticated grey matter, and that comes at an evolutionary cost.

Now, a new investigation into the immediate trade-off that occurs inside us when we have to think fast and work hard at the same time is the first to demonstrate that - while both are impaired - our mental ability is less affected than our physical capacity.

Researchers say that the findings suggest a "preferential allocation of glucose to the brain", which they argue is likely to be an evolved trait - as prioritising quick thinking over fast moving, for example, may have helped our species survive and thrive.

Scientists from the University of Cambridge's PAVE (Phenotypic Adaptability, Variation and Evolution) research group tested 62 male students drawn from the University's elite rowing crews. The participants had an average age of 21.

The rowers performed two separate tasks: one memory, a three minute word recall test, and one physical, a three minute power test on a rowing machine.

They then performed both tasks at once, with individual scores compared to those from previous tests. As expected, the challenge of rowing and remembering at the same time reduced both physical and mental performance.

However, the research team found that change in recall was significantly less than the change in power output.

During the simultaneous challenge, recall fell by an average of 9.7%, while power fell by an average of 12.6%. Across all participants the drop in physical power was on average 29.8% greater than drop in cognitive function.

The team say the results of their new study, published today in the journal Scientific Reports, add evidence to the 'selfish brain' hypothesis: that the brain has evolved to prioritise its own energy needs over those of peripheral organs, such as .

"A well-fuelled brain may have offered us better survival odds than well-fuelled muscles when facing an environmental challenge," said Dr Danny Longman, the study's lead author from the PAVE team in Cambridge's Department of Archaeology.

"The development of an enlarged and elaborated brain is considered a defining characteristic of human evolution, but one that has come as a result of trade-offs.

"At the evolutionary level, our brains have arguably cost us decreased investment in as well as a shrunken digestive system.

"Developmentally, human babies have more stored fat than other mammals, acting as an energy buffer that feeds our high cerebral requirements.

"On an acute level, we have now demonstrated that when humans simultaneously experience extremes of physical and mental exertion, our internal trade-off preserves cognitive function as the body's priority."

The adult brain derives its energy almost exclusively from the metabolism of glucose. Yet skeletal muscle mass is also energetically expensive tissue, accounting for 20% of the human male 'basal metabolic rate' - the energy used when doing nothing.

Longman says a limited supply of blood glucose and oxygen means that, when active, skeletal muscle becomes a "powerful competitor" to the brain. "This is the potential mechanism for the fast-acting trade-off in brain and muscle function we see in just a three minute window."

"Trade-offs between organs and tissues allow many organisms to endure conditions of deficit through internal prioritising. However, this comes at a cost," said Longman.

He points to examples of this trade-off in humans benefiting the brain. "The selfish nature of the brain has been observed in the unique preservation of mass as bodies waste away in people suffering from long-term malnutrition or starvation, as well as in children born with growth restriction."

Explore further: Could too much sitting be bad for our brains?

More information: Daniel Longman et al, A trade-off between cognitive and physical performance, with relative preservation of brain function, Scientific Reports (2017). DOI: 10.1038/s41598-017-14186-2

Related Stories

Could too much sitting be bad for our brains?

July 27, 2017
In many aspects of life where we need to use our brain power, we also tend to sit down: at school, at work, sitting exams or concentrating on a crossword. In a new paper, we explore how prolonged sitting may affect the brain's ...

The body and the brain: The impact of mental and physical exertion on fatigue development

July 30, 2015
Do you ever notice how stress and mental frustration can affect your physical abilities? When you are worried about something at work, do you find yourself more exhausted at the end of the day? This phenomenon is a result ...

High-fat diet starves the brain

April 29, 2016
A high-fat diet of three days in mice leads to a reduction in the amount of glucose that reaches the brain. This finding was reported by a Research Group led by Jens Brüning, Director at the Max Planck Institute for Metabolism ...

Sleep biology discovery could lead to new insomnia treatments that don't target the brain

August 11, 2017
UCLA scientists report the first evidence that a gene outside the brain controls the ability to rebound from sleep deprivation—a surprising discovery that could eventually lead to greatly improved treatments for insomnia ...

Brain cells mobilize sugar in response to increased activity

January 24, 2017
New research is providing insights into why the brain is so reliant on sugar to function.

Glucose war between brain and brawn—the hidden battle in children that made us human

November 20, 2014
The Proceedings of the National Academy of Sciences recently published a paper that showed a close link between the slow growth of children and the high glucose consumption of their brains. The proposed explanation: by saving ...

Recommended for you

Researchers investigate changes in white matter in mice exposed to low-frequency brain stimulation

June 19, 2018
A team of researchers at the University of Oregon has learned more about the mechanism involved in mouse brain white matter changes as it responds to stimulation. In their paper published in Proceedings of the National Academy ...

Left, right and center: mapping emotion in the brain

June 19, 2018
According to a radical new model of emotion in the brain, a current treatment for the most common mental health problems could be ineffective or even detrimental to about 50 percent of the population.

Cell type and environment influence protein turnover in the brain

June 19, 2018
Scientists have revealed that protein molecules in the brain are broken down and replaced at different rates, depending on where in the brain they are.

Often overlooked glial cell is key to learning and memory

June 18, 2018
Glial cells surround neurons and provide support—not unlike hospital staff and nurses supporting doctors to keep operations running smoothly. These often-overlooked cells, which include oligodendrocytes and astrocytes, ...

Electrically stimulating the brain may restore movement after stroke

June 18, 2018
UC San Francisco scientists have improved mobility in rats that had experienced debilitating strokes by using electrical stimulation to restore a distinctive pattern of brain cell activity associated with efficient movement. ...

Neuroscientists map brain's response to cold touch

June 18, 2018
Carnegie Mellon University neuroscientists have mapped the feeling of cool touch to the brain's insula in a mouse model. The findings, published in the June 15 issue of Journal of Comparative Neurology, provide an experimental ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

EnricM
not rated yet Oct 21, 2017
Crap, thus no coding while doing 400m intervals.
It's not fair :_(

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.