15 February 2006
Brain scans predict cognitive decline in normal people
Brain scans may detect neurological changes in people who exhibit no outward signs of cognitive decline but who later develop dementia or mental impairment, according to the results of a new study led by Berkeley researchers.
The study, published Feb. 8 in the journal Annals of Neurology, provides encouraging evidence that positron-emission tomography (PET) and magnetic-resonance imaging (MRI) could eventually be used to detect pre-clinical signs of Alzheimer's disease.
"Our paper is one of the few to show that it is possible to detect changes in the brains of normal older people who experience subsequent cognitive decline," said William Jagust, professor of neuroscience and public health and lead author of the paper. "We don't have enough data, yet, to say that the brain scans can predict Alzheimer's disease. However, the locations of the affected brain regions have been associated in other studies with Alzheimer's, so it's possible that we are picking up early signs of the disease."
The brain-imaging study is a substudy of the Sacramento Area Latino Study on Aging (SALSA), the first and only representative study of dementia and cognitive functioning in a Latino population. SALSA, funded by the National Institute on Aging, includes 1,789 people, primarily Mexican American, who were recruited by mail, telephone, and door-to-door solicitation.
For the imaging substudy, 60 cognitively normal participants received baseline PET and MRI brain scans and underwent a full battery of neuropsychological tests at enrollment. They were followed for an average of 3.8 years, taking cognition and memory tests approximately once a year. Individuals with significant declines in their scores were evaluated further for signs of cognitive decline.
The PET scans detected areas of lower glucose metabolism in the parietal and temporal lobes of the brain, the same regions shown in many other studies to have lower glucose metabolism in Alzheimer's patients and in some people with mild cognitive impairment.
In the imaging substudy, the MRI scans focused on the entorhinal cortex and hippocampus regions in the temporal lobe of the brain, areas that are involved in memory. Other post-mortem studies of the brains of Alzheimer's patients indicate that these regions are the first to become affected as the disease develops.
The researchers found that the smaller these brain regions were in the MRI scans, the more an individual's score declined on a delayed-recall memory test. These results are also in line with findings from other studies that link the size of the entorhinal cortex and hippocampus in people with mild cognitive impairment with the eventual development of Alzheimer's disease.
"In a project of this size, it's not realistic to expect the brain scans to predict Alzheimer's," said Haan. "But there is enough information to say that PET and MRI scans can predict subsequent cognitive decline in a population of cognitively normal people."
The researchers note that prior research on Alzheimer's focused primarily on people who had already developed mild symptoms of cognitive loss or on post-mortem analyses of the brains of Alzheimer's patients.
"By the time people who are already sick are identified, it's often too late to slow down the progression of Alzheimer's," said Mary Haan, professor of epidemiology at the University of Michigan and SALSA principal investigator. "By identifying early changes that could predict the development of dementia, it may also be possible to link those changes to primary risk factors that could be altered."
Options are now limited for identifying those who may go on to develop Alzheimer's disease. Few genetic factors have been identified, and the ones that have are only applicable to a minority of people who go on to develop the disease.
- Sarah Yang
A more competitive political landscape?
Redistricting reform could increase the competitiveness of some California congressional and legislative districts, according to a new study released last week by the Institute of Governmental Studies.
After drawing dozens of potential redistricting plans, researchers concluded that attempting to create more-competitive seats while also balancing other criteria would probably produce 12 to 14 competitive congressional districts and 12 to 17 competitive assembly seats. Currently, the state has no congressional districts and only five assembly districts that fall within the study's definition of a competitive range. Increased competitiveness has been one of the outcomes sought by those aiming to take the process of redrawing legislative districts out of the hands of the legislature.
The study cautions, however, that while such districts would be closely divided along partisan lines, they would not necessarily produce frequent partisan turnover. Factors such as incumbency, monetary advantages, national political trends, and candidate quality make it unlikely that closely divided districts would ensure a sharp increase in the frequency with which seats change hands, researchers found.
The ability of any redistricting plan to create a high rate of partisan turnover is "greatly limited," the researchers wrote.
Researchers produced a series of redistricting plans using various criteria, including increased competitiveness, respect for city and county boundaries, compactness, contiguity, the requirements of the voting-rights act, and equality of population. They did not use incumbent addresses, information that is typically included in current redistricting plans, nor did they consider communities of interest.
Researchers then analyzed the number of new districts likely to contain a registration advantage of less than 3 percentage points for Republicans or 10 percentage points for Democrats. That range is considered a closely divided district, since Republicans generally have a higher rate of turnout than Democrats.
The analysis was based on official state redistricting data from the California Statewide Database housed at IGS. The study was conducted by Bruce Cain, director of IGS and professor of political science; Karin MacDonald, director of the Statewide Database; and Iris Hui, a graduate student in political science. Maps and data are available at igs.berkeley.edu/redistricting_research/.
- Janet Gilmore