Date:
January 23, 2003
Contact: Dan Page ( dpage@support.ucla.edu
)
Phone: 310-794-2265
Using newly developed imaging techniques, UCLA neuroscientists
for the first time have "unfolded" the brain's
sea-horse-shaped hippocampus to reveal how dynamic activity
within the brain structure's complex architecture orchestrates
memory formation. Details appear in the Jan. 24 edition
of the peer-reviewed journal Science.
The researchers used extremely high-resolution functional
magnetic resonance imaging (fMRI) and software developed
at UCLA's Ahmanson-Lovelace Brain Mapping Center to
study blood flow within the hippocampus as 10 human
volunteers learned to associate names with faces.
The study identified areas within the hippocampus —
the cornu ammonis and the dentate gyrus — as highly
active only during encoding of the face-name pairs.
This activity decreased as associations were learned.
The subiculum, another area of the hippocampus, was
active primarily during the retrieval of the face-name
associations. Activity in the subiculum also decreased
as retrieval became more practiced.
Previous studies have demonstrated the importance of
the hippocampus in forming memories. However, no studies
until now have directly examined how activity patterns
within specific substructures change during learning.
"Our findings demonstrate that memory formation
is a dynamic process, with subdivisions within the hippocampus
making distinct but changing contributions as learning
takes place," said lead author Michael M. Zeineh,
a Brain Mapping Center researcher and student in the
David Geffen School of Medicine's Medical Scientist
Training Program. "Brain activity increases as
information is introduced, then diminishes as the new
information becomes better learned.
"As knowledge about the brain's complex circuitry
grows, neuroscientists will be better able to understand
and address a host of debilitating neurological disorders,
from Alzheimer's disease to epilepsy to damage caused
by head injuries," Zeineh said.
The brain's hippocampus is located on the floor of
each lateral ventricle. The debilitating effects of
damage to the hippocampus were highlighted in the 2001
feature film "Memento," which told the story
of a man who struggles to track his wife's killer despite
a head injury that destroys his ability to form short-term
memories.
The UCLA study used fMRI to scan the brains of volunteers
as they viewed information using goggles with a TV display.
Researchers first introduced pairs of names and faces
in sequence and instructed volunteers to learn which
face corresponded to which name. In order to distract
the subject to prevent rote rehearsal, researchers then
asked the volunteers to focus on a crosshair on the
screen and report any change. Finally, the researchers
showed the volunteers the earlier faces at random, asking
them to recall the name associated with each. The process
was repeated five times over eight minutes.
Researchers used the scans to evaluate blood-oxygen
level dependent signals. When the brain becomes active,
blood flow increases. The magnetic properties of hemoglobin,
a protein in red blood cells that carries oxygen to
body tissues, vary depending on the level of oxygenation.
These differences can be detected by fMRI.
Other UCLA researchers on the team were Stephen A.
Engel of the Department of Psychology; Paul M. Thompson
of the Laboratory of Neuroimaging and Department of
Neurology; and Susan Y. Bookheimer of the Ahmanson-Lovelace
Brain Mapping Center and Department of Psychiatry and
Biobehavioral Sciences, Division of Brain Mapping.
Funding for the study was provided the National Institute
of Mental Health, the National Institutes of Health,
the UCLA Interdepartmental Neuroscience Program, the
UCLA Medical Scientist Training Program, the Brain Mapping
Medical Research Organization, the Brain Mapping Support
Foundation, the Pierson-Lovelace Foundation, the Tamkin
Foundation, the Jennifer Jones-Simon Foundation, the
Capital Group Companies Charitable Foundation, the Robson
Family, the Northstar Fund and the National Center for
Research Resources.
The Ahmanson-Lovelace Brain Mapping Center at UCLA
seeks to improve understanding of the brain in health
and disease, through the comprehensive and quantitative
study of its structure and function.
The Medical Scientist Training Program at UCLA, in
conjunction with the California Institute of Technology
(Caltech), educates and trains exceptionally qualified
individuals for careers in biomedical science. The MSTP
requires an average of seven years of study leading
to both the M.D. and Ph.D. degrees.
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