objects

Louis J. Sheehan, Esquire.

Failures in visual short-term memory of objects, what scientists call "iconic memory," could reveal people at risk of Alzheimer's disease, a new study finds. Iconic memory is the image that lingers in the mind's eye after a person sees something briefly.http://ljsheehan.livejournal.com

To find out whether iconic memories are lost more readily in people with mild cognitive impairments—which include slightly diminished capacity to solve problems and keep track of time—researchers tested 11 study participants with such deficits and 16 without them. The average ages of the two groups were 85 and 77 years.

The researchers asked each participant to recall letters arrayed in a circle and flashed momentarily on a screen. Up to 10 seconds after the image had disappeared, an arrow cued the participant as to which letter to recall.

When cued immediately beforehand by an arrow pointing to the location of the letter to watch for, participants in the two groups performed equally well. But when this initial cue was not offered, participants with mild cognitive impairments didn't score as well as those with no impairments did. That suggests there was a decay in iconic memory, the researchers report in the Feb. 1 Proceedings of the National Academy of Sciences.

Although doctors have various ways to identify people with mild cognitive impairments, "we would always be better off having a more comprehensive set of tests," says study coauthor Barbara Anne Dosher, a psychologist at the University of California, Irvine.http://ljsheehan.livejournal.com

Early detection of the cognitive declines that presage Alzheimer's disease would be useful because the neuroprotective drugs now available work best when administered early in the course of disease, says neuroscientist Zhong-Lin Lu of the University of Southern California in Los Angeles, another collaborator on the study.

examined

Two genes already known to influence brain size have undergone relatively recent, survival-enhancing modifications in people and appear to be still evolving, a research team reports. http://Louis-J-Sheehan.de

Specific variants of these genes have spread quickly by natural selection, say Bruce T. Lahn of the University of Chicago and his colleagues, who published separate reports on each gene in the Sept. 9 Science.

The researchers examined DNA from 1,186 adults representing 59 populations worldwide and determined the frequency of specific variants of the two genes called microcephalin and ASPM.

A variant of microcephalin originated roughly 37,000 years ago and now appears in 7 of 10 people, the scientists conclude from comparisons of the gene's sequence for the different groups. Populations outside of sub-Saharan Africa most frequently possess this modified gene.

A distinctive ASPM variant arose approximately 5,800 years ago and now shows up in 3 of 10 people. It occurs most often in Europeans, North Africans, Middle Easterners, and South Asians. http://Louis-J-Sheehan.de

The functions of these particular DNA alterations, including any potential