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.
References
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
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