The brain is a thirsty organ

The brain needs constant nourishment from oxygen-rich blood, and when the heart stops-as happens during sudden Cardiac arrest-the result can be devastating. Brain cells die, and memory and other brain functions begin to wither.

Researchers led by cardiologist Neil Grubb of the Royal Infirmary of Edinburgh have now measured the damage. They used Magnetic resonance imaging (MRI) to scan 9 cardiac arrest patients, and found a decrease of 14 percent in overall brain volume. Team member Ronan O'Carroll of the University of St. Andrews reported the results of the study last October at the Society for Neuroscience meeting in Miami Beach, Florida.

In an earlier study of 35 cardiac-arrest patients, the researchers had found that all but 7 had suffered mild to severe memory loss. The impairments showed up in the ability to remember names, appointments, and the location of personal items. As a result, the researchers expected to find most of the damage in the hippocampus, a part of the brain that helps transform recent experiences into enduring memories. But the damage, says O'Carroll, showed up throughout the brain.

To John Walker, a neuropsychologist at the University of California at San Francisco, this shows the importance of thoroughly testing people who have suffered a cardiac arrest. Walker and Mary J. Sauve, a Ph.D. in nursing at UCSF, have discovered that-in addition to memory loss-patients' ability to process information is also impaired. This suggests damage to multiple brain centers. "It's important to understand what has gone wrong in order to devise an appropriate rehabilitation strategy," Walker says.