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DURHAM, N.C. -- Younger and older adults depend primarily on
different areas of their brain to process visual information,
Duke University Medical Center researchers have found. Their
brain imaging studies of visual attention revealed that young
people tend to use "bottom-up" areas of the brain that are
involved in processing the visual features of a scene.

By contrast, older people make greater use of brain areas
involved in "top-down," or goal-directed processing. The former
area is in the lower back, or occipital area of the brain,
while the latter area is in the front and upper back, or
parietal, brain areas that control higher functions such as
speech, thought, planning for the future and interpretation of
spatial orientation.

The researchers said their findings provide new insight into
how the brain adjusts its thinking processes as people age.
Such studies also yield clues to the underlying causes of
cognitive decline with aging, they said.

The results of the Duke experiments were published online
March 1, 2006, in the journal Neurobiology of Aging. The study
was supported by the National Institute on Aging.

For their studies, the researchers used functional MRI
(fMRI) to image the activation of gray matter during testing.
And, a relatively new imaging technique called diffusion tensor
imaging (DTI) allowed them to gauge the structural integrity of
the fibrous white matter. The gray matter of the brain is
responsible for information processing, while the white matter
enables information transmission among different areas of the
brain.

Functional MRI uses harmless magnetic fields and radio waves
to map blood flow in brain regions, which reflects brain
activity. DTI is an MRI-based technique that measures the
movement of water molecules throughout tissues. DTI can
determine the structural integrity of a brain region, and if
the structure is not intact, its ability to propagate neural
signals can be compromised.

By using the two different methods of imaging the brains of
volunteer subjects during vision tasks, the researchers found
that the structural integrity of the "white matter" within the
brain appears to play a role in which areas of the brain are
activated. Their imaging studies found that the age-related
decline in the white matter was more pronounced in frontal
regions of the brain.

"It appears that age-related cognitive changes are the
result of combined influences on the gray matter and the white
matter," said lead author David Madden, Ph.D., Duke behavioral
psychologist and researcher in aging.

"We need further studies to better understand how all these
different factors relate to each other, and which changes in
cognition result from normal aging or something else," he
continued. "Additional research combining fMRI, DTI and
behavioral performance will be valuable in determining the
neural mechanisms of age-related cognitive decline."

The goal of the team's experiments – which were among the
first to use both fMRI and DTI to study aging– was to better
understand any age-related changes in visual attention. By
using two different imaging methods, the researchers could
correlate attentional functioning of the gray matter as
measured by fMRI with structural integrity of the white matter
as measured by DTI.

The researchers recruited two groups of healthy volunteers –
those between 19 and 28 and those between 60 and 82. As the
volunteers took the same battery of visual tests that measured
top-down attention, the researchers scanned the subjects'
brains with fMRI and DTI to determine which areas of the brain
were activated. The tests involved correctly locating target
letters within a "slide show" of different images appearing on
a computer display.

"Based on past studies, we expected greater activation in
the frontal and parietal regions in the older adults,
especially when top-down attention was required," Madden said.
"We also hypothesized that an age-related related decline in
the white matter integrity in the frontal part of the brain
would correlate with changes in gray matter activation."

While the imaging studies did show the expected increase in
frontal and parietal area activation on the older subjects, the
team found only a limited support for the role of structural
integrity of the white matter as a mediator of age differences
in activation.

"We feel that results of our tests represent an important
first step understanding the complex relationships between
aging, brain structure and cognitive performance," Madden said.
"The brain can be very plastic in how it re-directs pathways
and functions in response to circumstances."

Madden and his team are currently planning future studies
using more sophisticated techniques to make more detailed
measurements of the way gray and white matter responds to
different cognitive tasks.

Other members of the Duke team included Julia Spaniol,
Barbara Bucur, James Provenzale, Roberto Cabeza, Leonard White
and Scott Huettel. Wythe Whiting, Washington and Lee
University, Lexington, Va., was also a member of the team.