In Early Alzheimer's, Brain Compensates

Feb. 7, 2003 -- For a window of time, early in the onset of Alzheimer's disease, the brain draws on all its resources to compensate for deficits that are developing. It's a new finding about this debilitating disease that could lead to new treatments.

The study, conducted by a group of Canadian researchers, appears in the Feb. 1 issue of the Journal of Neuroscience.

As Alzheimer's develops, people in the early stages have problems with what researchers call their "episodic" and "semantic" memory.

Semantic refers to the accumulation of general world knowledge gained over a lifetime -- like names of countries, famous people, major historical events. Episodic refers to events that one experiences through his or her life -- like having visited the dentist yesterday or graduating from college back in 1950.

In the early stages of this disease, there is increased activity in the front part of the brain -- called the prefrontal region -- when the person is performing memory tests.

In their small study, this group of researchers focused on 11 people who had symptoms of early-stage Alzheimer's disease and 12 older adults who didn't show memory problems.

All were shown a series of images on a computer screen, then were asked a series of questions: Was the object a living or a nonliving thing? Was it a new item or an old item?

Overall, the Alzheimer's patients missed more questions. However, there was a wide range of scores in the Alzheimer's group, reports lead researcher Cheryl Grady, senior scientist at the Rotman Research Institute in Toronto.

Some performed poorly and others performed within the normal range, she says. For those who did better on the memory tasks, researchers found that these patients were able to recruit the prefrontal region to compensate for the loss of memory function.

This is the first time that scientists have established a direct link between good performance on tests and this compensatory brain activity, Grady writes.

Unfortunately, this compensatory effect diminishes as the disease progresses, Grady write. However, her findings could lead to more effective treatments that extend this compensatory effect -- and delay the degenerative effects of Alzheimer's for longer periods.