Inside Your Brain on Holiday

Sit back, close your eyes, relax for a minute and allow your mind to wander wherever it wants to go. Don’t try to think of anything… Have you ever wondered what is going on inside your brain when your mind isn’t doing anything in particular, just like a moment ago? It turns out quite a lot. One of the most astonishing qualities of the brain is its voracious appetite for energy. It accounts for only 2% of body weight, yet it burns an amazing 20% of the total calories consumed by the body. So you might think that the brain at rest would be conserving energy until the next task, but this is hardly the case. The energy consumption of the brain at rest decreases by only 5% compared to a brain at full capacity. Scientists have named the energy consumed during rest the brain’s “dark energy,” since the massive energy consumption during this so-called rest period is one of the biggest mysteries in neuroscience today.

Scientists call the state of the brain at rest the default mode network (DMN), which can be described as a discrete collection of brain regions that exhibit greater activity during rest periods than during performance in effortful cognitive tasks. This pattern of activity is associated with daydreaming as well as light sleep. While researchers have not determined the full range of processes that the brain undergoes at rest, recent evidence has revealed that resting brain abnormalities are associated with schizophrenia, depression, autism and Alzheimer’s disease.

In a recent study published in PLoS One, researchers in Japan at Tohoku University found a link between the DMN and general intelligence and creativity.

Researchers scanned the brains of 63 healthy volunteers during rest using functional MRI to measure the cerebral blood flow (CBF) in different regions of the brain. CBF is a way to measure brain activity since regions with greater activation demand more oxygen delivery via blood. To measure general intelligence, researchers administered a standard psychometric test to volunteers. Creativity was assessed using a divergent thinking test, which assesses the ability to think in unique ways and generate novel ideas rapidly.

Brain imaging revealed that individuals who scored higher on measures of intelligence also showed higher blood flow in the gray and white matter of the brain at rest. Similarly, individuals who demonstrated greater creativity exhibited higher blood flow in regions of white matter at rest, but not gray matter.

So what does this mean, exactly?

Well, gray matter is the portion of brain tissue consisting mainly of nerve cell bodies, which may be thought of as the processing center of the nerve cell. White matter consists of nerve fibers covered by myelin, a protein coating responsible for the white appearance, which transmit electrical signals from one nerve cell to another. To use a computer network as an analogy, the gray matter would be the actual computers and the white matter is the network cables connecting the computers together.

The authors of this study speculate that more blood flow to gray and white matter in individuals with higher intelligence may be an indication that they have intrinsically more active brains. It’s possible that brains that are more active at rest are undergoing specific biochemical processes to increase the integrity and efficiency of the system.

Creative individuals also showed more white matter blood flow, but no difference in gray matter. This makes sense because white matter is involved in the overall connectivity of the brain and a key aspect of divergent and novel types of thinking is greater communication among distinct regions of the brain.

These results offer exciting clues to the function of the brain’s mysterious dark energy. The brain is not a machine that has an ON and OFF state. Instead, the brain is a dynamic system engaging in integral processes continuously, especially when we’re unaware of it, as with daydreaming and sleep.

Insights from research on the brain’s DMN suggest an alternative to the old adage “an idle mind is the devil’s workshop.” As the great mathematician Henri Poincaré observed regarding his own creative process, “Often nothing good is accomplished at the first attack. One takes a rest; and then all of a sudden the decisive idea presents itself to the mind.” Indeed, an idle mind may be an extremely useful tool for solving a problem, coming up with an innovation, or simply maintaining a healthy brain.


Buckner RL, Andrews-Hanna JR, & Schacter DL (2008). The brain’s default network: anatomy, function, and relevance to disease. Annals of the New York Academy of Sciences, 1124, 1-38 PMID: 18400922

Raichle ME (2009). A paradigm shift in functional brain imaging. The Journal of neuroscience : the official journal of the Society for Neuroscience, 29 (41), 12729-34 PMID: 19828783

Takeuchi H, Taki Y, Hashizume H, Sassa Y, Nagase T, Nouchi R, & Kawashima R (2011). Cerebral blood flow during rest associates with general intelligence and creativity. PloS one, 6 (9) PMID: 21980485

Image via bendao / Shutterstock.

  • I’m a stroke survivor and I once heard that if you are thinking hard your brain can use up to 50% of your energy. Survivors are incredibly fatigued all the time. I hypothesize that our brains are consuming 90-100% of the available energy because we have to concentrate incredibly much on directing movement rather than having unconscious processes doing the work. And this is before we get to the fact that physically the unaffected side is working twice as hard and the affected side is maybe 50% efficient. In my case my cardiovascular fitness puts me at the level of an athlete yet I am totally fatigued all the time. Your thoughts on the matter?

    • Thanks for your comment Dean. I can’t comment on the exact percentages of energy expenditure, but you make a good point that because some of the unconscious processes that you learned as a child have to be relearned as an adult much more energy is required by the brain. This makes sense since there is good evidence that when a task can be performed by “unconscious” regions then less concentration and attentional resources are required, whereas when we are learning new skills we rely more heavily on attention and working memory processes, which are supported by the prefrontal cortical areas – probably some of the most energy consuming areas of the human brain. Thanks for contributing some first-hand perspective to this matter.

      • onergk69

        In general, the brain utilizes about 20% of the body’s energy, more than any other organ system.


  • gregorylent

    i so wish neuro people would flip their model .. the one that says the brain makes consciousness … reversing that, research such as the above would go soooo much faster … and please, distinguish between attention/awareness/consciousness, there are real reasons why we have different words for these things.

    • AnnA

      You are making derogatory comments on “neuro pople” when his article wasn’t even about consciousness. Therefore, he wouldn’t have to differentiate attention, awareness, or consciousness. He was pointing out the fact that the brain uses only 5% less energy at rest.

    • jytdog

      i wonder why you think they don’t. neuroscientists are scientists; they study material things….in other words, the brain.

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Stephen Dougherty, MS

Stephen Dougherty, MS, is a freelance science and medical writer with experience developing medical education materials and multimedia learning applications. He has worked for several years as a researcher in cell biology and neurobiology and holds a Masters of Science in Behavioral Neuroscience.

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