In my research on Alzheimer’s and glucose metabolism, I ran across a fascinating article about the brain’s default system-that part of the brain that is affected in Alzheimer’s Disease; that part of the brain that hogs glucose like no other part of the brain.

In The Secret Life of the Brain, Douglas Fox brings together research on the default network beginning with Dr. Sokoloff who, in his attempt to find out why the brain uses so much glucose (20% of the body’s supply), discovered that the brain uses as much energy while “at rest” as it does while performing tasks.

Later, a neuroscientist named Marcus Reichle discovered a kind of “brain within the brain” that works its butt off when it’s supposedly in “idle mode.”

Raichle and Shulman published a paper in 2001 suggesting that they had stumbled onto a previously unrecognised “default mode” - a sort of internal game of solitaire which the brain turns to when unoccupied and sets aside when called on to do something else. This brain activity occurred largely in a cluster of regions arching through the midline of the brain, from front to back, which Raichle and Shulman dubbed the default network (Proceedings of the National Academy of Sciences, vol 98, p 676).

It was found that some parts of this network devoured 30 per cent more calories, gram for gram, than nearly any other area of the brain. Since part of this default system is in constant communication with the hippocampus (which records every day memories), Reichler speculated that its function was to sort, evaluate, and categorize memories in such a way that would allow the brain to use the past as an “inner rehearsal” for considering future actions and choices.

Brilliant. Just when you think daydreaming is a waste of time, it turns out it’s crucial for living.

Raichle now believes that the default network is involved, selectively storing and updating memories based on their importance from a personal perspective - whether they’re good, threatening, emotionally painful, and so on. To prevent a backlog of unstored memories building up, the network returns to its duties whenever it can.

In support of this idea, Raichle points out that the default network constantly chatters with the hippocampus. It also devours huge amounts of glucose, way out of proportion to the amount of oxygen it uses. Raichle believes that rather than burning this extra glucose for energy it uses it as a raw material for making the amino acids and neurotransmitters it needs to build and maintain synapses, the very stuff of memory. “It’s in those connections where most of the cost of running the brain is,” says Raichle.

Reichler later attented a lecture by an Alzheimer’s specialist and was shown a map of beta amyloid plaques (those clumps found in Alzheimer’s autopsies) in the brain. The picture looked exactly like the default network!

Raichle, Greicius and Buckner have since found that the default network’s pattern of activity is disrupted in patients with Alzheimer’s disease. They have also begun to monitor default network activity in people with mild memory problems to see if they can learn to predict who will go on to develop Alzheimer’s. Half of people with memory problems go on to develop the disease, but which half? “Can we use what we’ve learned to provide insight into who’s at risk for Alzheimer’s?” says Buckner.

That got me thinking…

Maybe one reason we lose memories is that our lifestyle doesn’t allow for much rich idle time like when we would sit on the porch sipping sweet tea on a hot afternoon. So the default network can never do its work of sorting and categorizing memories, and consequently we lose them.

And if this is a problem with the present generation, how much moreso for the upcoming generation. We are consumed with having something to pay attention to all the time. Just look at TV screens these days: not only do you have the main screen, but there’s the pop-up ad for the “next show,” a caption for what’s going on on the screen, and a ticker at the bottom of the screen for what’s happening elsewhere.

Maybe part of the solution for AD is the “quiet space” to be incorporated in school, at work, and at home. Hmm, come to think of it, I offered this very solution in a comment to an article in Time Magazine back in 09 (Turn Off, Tune In, Log Out):

I predict that the twitterification of our society is going to lead to an exponential increase in early-onset Alzheimer’s. We’re increasing the rate of input to our brains and decreasing the time for processing information, and our brains are going to revolt. That, in turn, will lead to the next big industry: de-twitterification rooms where you can sit alone and unconnected, with nothing but a giant aquarium and a beanbag. -Marty

SEE ALSO Language and the Brain’s Default Network in Alzheimer’s