The Brain’s Dark Energy

If I said dark energy, you would probably think of some magic spell, or, given that this comes from Scientific American, the mysterious physical substance that constitutes 74% of our universe.

In Scientific American‘s March 2010 issue, the featured article “The Brain’s Dark Energy” by Marcus E. Raichle discusses a new type of dark energy—a type not in cosmology, but in neuroscience. Here’s the gist of it:

We previously thought that the human brain is at a low-energy rest state when a person is at rest, and goes into a more active state when a person is active, that is, performing some thought-provoking task. Recent findings from improved brain scans, however, show that the brain’s activity level is already very high at rest, and when active, increases by just 5%. In other words, the resting state consumes 20 times more energy than does the addition caused by active state. This high energy level in the brain’s resting, or default, mode was labeled dark energy, aptly so after the astronomical sense of dark energy, with which it shares many similarities.

All the substances in the universe we can see and interact with—all this together makes up less than 5% of the universe, with dark energy and dark matter at 74% and 23% respectively. In the same way, all the brain activity we are aware of—conscious thought—makes up about 5% of our total brain activity. Just as background energy in the universe is predominent, so is background energy in our brains. Dark energy is thus a fitting term for this phenomenon.

The article introduces a newly discovered brain system called the default mode network (DMN), for which the specifics are still being studied. The role of the DMN is essentially to orchestrate the actions of other systems in the brain; in fact, the author likens the function of the DMN to that of an orchestra conductor—to issue timing signals and to coordinate others in preparation for future events.

Implications of the DMN include much-needed insights into the understanding of consciousness, which is right now still a mysterious subject. We’ll take a look at attention, for instance. What if you had the attention span to get this far down my post, but your focus is now beginning to wander? What if I could see the neural activity of your brain in real time? What if I saw 30 seconds ago that your DMN was shutting off your brain’s conscious area, thus telling me that you will lose focus soon—about right now? And what if I told you that this type of prediction is possible, and has already been done, tested, and verified? (By the way, it has.)

Besides unlocking the nature of consciousness, dark energy could also provide new frameworks for brain diseases, in particular, Alzheimer’s, depression, and schizophrenia. For instance, the areas of the brain affected by Alzheimer’s are virtually the same as the areas that comprise the DMN. Depression has been linked to a decreased amount of connections between the DMN and areas controlling emotion. Schizophrenia, on the other hand, corresponds to increased signalling in the DMN, a finding still under investigation.