The brain areas involved in daydreaming, musing and other stream-of-consciousness thoughts appear to be the same regions targeted by Alzheimer's disease, researchers are reporting today in an unusual study that offers new insights into the roots of the deadly illness.
The strong correlation between the two suggests there might be a link between the sort of thinking that people regularly do when not involved in purposeful mental activity and the degenerative disease that is characterized by forgetfulness and dementia, said scientists who conducted the federally funded study.
Randy Buckner, a neuroscientist at Washington University in St. Louis, said the implications of the finding are far from clear. It is too early to suggest that daydreaming is dangerous, he said, or that avoiding such musings could affect the risk of Alzheimer's disease. Rather, he and others said, the study adds to the evidence that everyday mental and physical activities play an important role in the course of neurological disease.
"It suggests an avenue between brain activity patterns and Alzheimer's disease that we just hadn't been thinking about," said Buckner, who led the study. "It is going to take some time to understand the relative potential of this link."
Other neuroscientists agreed the work was intriguing -- and joked about its implications.
"There goes half my day," Ronald Petersen, director of the Mayo Clinic's Alzheimer's Disease Research Center, said about his own propensity for creative musing.
"It is really going out on a limb," he added of the new study. "But for the sake of generating discussion, it is interesting. It is useful to get people thinking along these lines."
Further research is underway to probe the link, said Buckner, who is affiliated with the Howard Hughes Medical Institute in Chevy Chase. While some unknown third factor may be responsible for triggering daydreaming as well as Alzheimer's, the neuroscientist said a causative link between the two would explain a mystery that has long bothered scientists: why Alzheimer's generally affects memory first.
"When we muse to ourselves and plan our day and think about the recent past, we tend to use memory systems," Buckner said. "Through some as-yet-unknown pathway or metabolism cascade, use of these systems may be what underlies Alzheimer's disease."
Although daydreaming is usually seen as intellectual downtime, Buckner said that might not be true. Such musings are far from passive, he added, and might help people be creative.
But the undirected thought patterns that most people slip into readily may result in the kind of "wear and tear" that ends in Alzheimer's disease, Buckner said.
This theory, however, clashes with the evidence that intellectual activity plays a protective role against Alzheimer's disease. Far from the "wear and tear" model, other research has suggested that the brain runs on a "use it or lose it" system.
Buckner and other neuroscientists acknowledged the contradiction -- and put it down to the preliminary state of the research.
"To be honest, all of these should be taken with a grain of salt," Petersen said of the various theories of risk factors and protective factors. Because Alzheimer's typically strikes the elderly, high-quality, long-term studies that track people for decades are difficult to conduct.
Although Buckner's study focused on one aspect of Alzheimer's -- the buildup of amyloid plaques in the brains of patients -- Petersen said it is still not clear what role the plaque plays in the disease or how it is linked to another signature of the disease, tangles of nerve fibers. The tangles, Petersen said, may be more linked to changes in cognitive activity than the plaques.
The new study, which is being published today in the Journal of Neuroscience, made use of several advances in brain imaging. Different techniques allowed scientists to map the complex brain patterns of young adults while they were daydreaming and to compare those findings with more recent research pinpointing the location of amyloid plaques in the brains of Alzheimer's patients.
In all, Buckner's team used data from 746 participants. Buckner said he was surprised to find a "remarkable" correlation between the regions involved in daydreaming and the location of the plaques.
"I don't want to imply if one didn't do those things one would not get Alzheimer's disease," he said. "It may be that Alzheimer's disease arises from normal brain function. . . . It could be that while we are well positioned to lead long lives, we were not built to live as long as we do."
Lon Schneider, a psychiatrist at the University of Southern California, said the idea that Alzheimer's could be linked to repetitive thought patterns has parallels with diseases such as depression, in which repetitive worries and obsessions are linked to brain changes.
But, like the other scientists, he cautioned about drawing inferences about preventive techniques.
"I look forward to the public health campaign to stop people from engaging in these dangerous, risky behaviors," he quipped. "Maybe we can equip ourselves with anti-daydreaming monitors that shock us when we slip into reverie."