Wednesday, July 07, 2010

the brain's dark energy

SciAm | Brain regions active when our minds wander may hold a key to understanding neurological disorders and even consciousness itself.

Imagine you are almost dozing in a lounge chair outside, with a magazine on your lap. Suddenly, a fly lands on your arm. You grab the magazine and swat at the insect. What was going on in your brain after the fly landed? And what was going on just before? Many neuroscientists have long assumed that much of the neural activity inside your head when at rest matches your subdued, somnolent mood. In this view, the activity in the resting brain represents nothing more than random noise, akin to the snowy pattern on the television screen when a station is not broadcasting. Then, when the fly alights on your forearm, the brain focuses on the conscious task of squashing the bug. But recent analysis produced by neuroimaging technologies has revealed something quite remarkable: a great deal of meaningful activity is occurring in the brain when a person is sitting back and doing nothing at all.

It turns out that when your mind is at rest—when you are daydreaming quietly in a chair, say, asleep in a bed or anesthetized for surgery—dispersed brain areas are chattering away to one another. And the energy consumed by this ever active messaging, known as the brain’s default mode, is about 20 times that used by the brain when it responds consciously to a pesky fly or another outside stimulus. Indeed, most things we do consciously, be it sitting down to eat dinner or making a speech, mark a departure from the baseline activity of the brain default mode.

Key to an understanding of the brain's default mode has been the discovery of a heretofore unrecognized brain system that has been dubbed the brain's default mode network(DMN). The exact role of the DMN in organizing neural activity is still under study, but it may orchestrate the way the brain organizes memories and various systems that need preparation for future events: the brain's motor system has to be revved and ready when you feel the tickle of a fly on your arm. The DMN may play a critial role in synchronizing all parts of the brain so that, like racers in a track competition, they are all in the proper "set" mode when the starting gun goes off. If the DMN does prepare the brain for conscious activity, investigations of its behavior may provide clues to the nature of conscious experience. Neuroscientists have reason to suspect, moreover, tat disruptions to the DMN may underlie simple mental errors as well as a range of complex brain disorders, from Alzheimer's disease to depression.

The ups and downs of the DMN may provide insight into some of the brain's deepest mysteries. It has already furnished scientists with fascinating insigts into the nature of attention, a fundamental component of conscious activity. In 2008 a multinatinal team of researchers reported that by watching the DMN, they could tell up to 30 seconds before a subject in a scanner was about to commit an error in a computer test. A mistake would occer if, at that time, the default network took over and activity in areas involved with focused concentration abated.

And in years to come, the brain's dark evergy may provide clues to the nature of consciousness. As most neuroscientists acknowledge, our conscious interactions with the world are just a small part of the brain's activity. What does on below the level of awareness - the brain's dark every, for one - is critical in providing the context for what we experience in the small window of conscious awareness. Fist tap Arnach.