Daydreaming linked to Alzheimer's disease

Aug 30 2005

According to new research, Alzheimer's disease may be due to abnormalities in the regions of the brain that operate the "default state", a term used to describe the cognitive state people defer to when musing, daydreaming, or thinking to themselves.

The researchers used five different medical imaging techniques to study the brain activity of 764 people, including those with Alzheimer's disease, those on the brink of dementia, and healthy individuals.

The team from Howard Hughes Medical Institute, Washington University in St. Louis, say that the default activity patterns of the brain may, over many years, augment a metabolic- or activity-dependent cascade that is a part of Alzheimer's pathology.

Lead author of the study, Randy L. Buckner, says the regions of the brain used in the default state when we are young, are very similar to the regions where plaques form in older people with Alzheimer's disease.

Buckner says the new findings are important because they could help scientists and clinicians identify and understand the beginnings of what is probably a chain of events that ultimately leads to Alzheimer's.

Alzheimer's is the most common form of dementia among older people, and is characterized by the erosion of language, thought and memory.

The brains of people with Alzheimer's disease, have abnormal clumps of plaque and tangled bundles of fibers and characterize the physical manifestation of the disease, which may affect as many as 4.5 million Americans.

The causes of the disease are unknown.

New imaging techniques and the use of bioinformatics and statistical methods enabled Buckner and his team to construct a picture of Alzheimer's.

In the process, the team unexpectedly saw that the regions of the brain that light up when we slip into comfortable patterns of thought are the same as those that, later in life, harbour the disabling clumps of plaque characteristic of Alzheimer's, a disease that as a rule manifests itself after age 60.

Buckner says that suggests that dementia may be a consequence of the everyday function of the brain, and the chain of events that leads to Alzheimer's begins at young adulthood.

Scientists have known for a while that when the mind is not concentrated on a task it switches to a default mode, a state of mind where we may muse, daydream or retrieve pleasant memories.

However it appears that when a young person is asked to concentrate on a specific task, they are easily able to shut off the default mode and the corresponding regions of the brain that run this mode.

With powerful new technologies scientists are now able to map the activity of the brain in its different states, including the default state, and they have already seen that when a person who has clinical Alzheimer's disease is asked to concentrate on a specific task, the default mode actually becomes more active, rather than showing less activity, as it would in a young, healthy adult.

According to Buckner, the default is characterized by metabolic activity in specific regions of the brain, notably the posterior and cortical regions.

He says the key insight is that brain activity and metabolism are not uniform across the brain, and when they looked at people on the edge of dementia, they saw a loss of brain tissue in the regions predicted.

Apparently it is clear that the memory systems of the human brain are vulnerable, and the memory systems are the ones often used in default states.

Buckner says this may help them to plan and solve the problems.

William Klunk, associate professor of psychiatry at the University of Pittsburgh and a co-author of the Journal of Neuroscience paper, says the findings may have future clinical implications as Alzheimer's is typically diagnosed when it is too late to intervene.

Klunk, has developed techniques for imaging the amyloid plaques in Alzheimer's patients and says the findings suggest that there is now the potential to begin to trace the patterns of the disease and develop methods to detect it before the clinical symptoms set in.

Buckner does say however that the idea of a causative relationship between everyday metabolic functions of the brain and Alzheimer's remains a hypothesis, and more work is needed to show if amyloid ( plaque ) deposition is really dependent on metabolism.

Buckner says they are very interested in exploring these new observations to understand who is at risk and who is protected from Alzheimer's.

The study is published in the current issue of the Journal of Neuroscience.