Wednesday, August 06, 2008

The Brain Unmasked

New imaging technologies reveal the intricate architecture of the brain, creating a blueprint of its connectivity.

By Emily Singer

Brain mapping: A variation on MRI called diffusion spectrum imaging allows scientists to map the neural fibers that relay signals in the brain. Each fiber in the image represents hundreds to thousands of fibers in the brain, each traveling along the same path. Credit: George Day, Ruopeng Wang, Jeremy Schmahmann, Van Wedeen, MGH

Multimedia   Click here for a tour of the brain via diffusion brain imaging.   To see an animation of the human brain network, click here.

The typical brain scan shows a muted gray rendering of the brain, easily distinguished by a series of convoluted folds. But according to Van Wedeen, a neuroscientist at Massachusetts General Hospital, in Boston, that image is just a shadow of the real brain. The actual structure--a precisely organized tangle of nerve cells and the long projections that connect them--has remained hidden until relatively recently.

Traditional magnetic resonance imaging, or MRI, can detect the major anatomical features of the brain and is often used to diagnose strokes and brain tumors. But advances in computing power and novel processing algorithms have allowed scientists to analyze the information captured during an MRI in completely new ways.

Diffusion spectrum imaging (DSI) is one of these twists. It uses magnetic resonance signals to track the movement of water molecules in the brain: water diffuses along the length of neural wires, called axons. Scientists can use these diffusion measurements to map the wires, creating a detailed blueprint of the brain's connectivity.

On the medical side, radiologists are beginning to use the technology to map the brain prior to surgery, for example, to avoid important fiber tracts when removing a brain tumor. Wedeen and others are now using diffusion imaging to better understand the structures that underlie our ability to see, to speak, and to remember. Scientists also hope that the techniques will grant new insight into diseases linked to abnormal wiring, such as schizophrenia and autism.

On the next page is an animation of the wiring of a marmoset monkey.