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New findings on exactly why our “idle” brains burn so much fuel

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"The human brain is a greedy organ," I wrote in my release describing a new Stanford study before elaborating:

Accounting for only 2 percent of the body’s weight, it consumes 20 percent of the body’s energy. Yet the rate at which the brain gobbles glucose (the fuel our brain cells run on) barely budges when we cease performing a physical or mental activity. Even at rest, the brain seems engaged in a blizzard of electrical activity, which neuroscientists have historically viewed as useless “noise.”

The study, which appears today in in Neuron, sheds light on why the brain paradoxically appears to exhaust so much energy in what at first glance seems akin to the idling of a car’s engine. Although you wouldn't know it from just staring at it, the human brain is a complicated orchestra of electrical circuits constantly humming along with one another over the comparatively long distances that separate one part of the organ from another.

Over the past decade, neuroscientists using brain-imaging methods have identified dozens of distributed, collaborative clusters of brain regions working in concert and dedicated to various mental activities from solving math problems to recalling what one ate for breakfast.

Now a team led by Stanford neuroscientist Josef Parvizi, MD, PhD, has tracked the electrical activity within and between these simultaneously pulsing clusters (or, in Neurospeak, "networks") with more precision than has previously been possible, and shown that these closely coordinated firing patterns persist even during sleep. This, in turn, may go a long way to explaining why when it comes to how fast the brain guzzles energy, the most intense thoughts, emotions or actions on our part barely budge the needle.

In their study, Parvizi and his colleagues were able to dig deeper than brain-imaging studies can usually go, because they could directly record electrical activity in selected areas in living human subjects' brains.

The areas in question are distinct parts of a well-studied brain network called the default mode network, which is perhaps the most energetic of the dozens that have so far been discovered. That's because the default mode network is most active when a person is at rest — lying still with eyes closed or just staring off into space  — or is retrieving an autobiographical memory (“What did I eat for breakfast?”).

Parvizi and his associates showed that the same pattern of coordinated electrical activity observed in the default mode network regions when experimental subjects were performing an autobiographical-memory task persisted even when those individuals were sound asleep.

It adds up to this, Parvizi told me: “The vast amount of energy consumption by our brain is due to its spontaneous activity at all times when we are not consciously involved in a specific task.”

It may be that, all through the night, the brain's circuits are talking to each other, taking each other's measure, and staying tuned for optimal function when day breaks. An idling engine puts you just one gas-pedal pump away from a fast take-off.

Previously: In a human brain, knowing a human face and naming it are separate worries, Mind-reading in real life: Study shows it can be done (but they'll have to catch you first), We've got your number: Exact spot inbrainwhere numeral recognition takes place revealed, Metamorphosis: At the push of a button, a familiar face becomes a strange one and Why memory and math don't mix: They require opposing states of the same brain circuitry
Photo by Don O'Brien

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