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A new look
at how Memory and Spatial Cognition are
related
Newswise — In a study that
sheds new light on how memory and spatial
cognition are related to each other in the
brain, researchers at the University of
California, San Diego School of Medicine and
the Veteran Affairs (VA) San Diego
Healthcare System studied memory-impaired
patients as they navigated their
environment.
Path integration, or the
ability of the brain to compute the distance
and direction of a traveled path, is an
important aspect of spatial cognition – an
ability long-thought to be dependent on the
medial temporal lobe structures of the
brain.
However, the researchers
discovered that the hippocampus and
entorhinal cortex – two major medial
temporal lobe structures – are not essential
for path integration. Their findings will be
published in the early on line edition of
Proceedings of the National Academy of
Sciences (PNAS) the week of August 4.
The study, led by Larry R.
Squire, Ph.D., professor of psychiatry,
neurosciences and psychology at UCSD School
of Medicine and research career scientist at
the VA San Diego Healthcare System, was
designed to measure whether these structures
of the brain are essential for spatial
cognition.
“For decades, the medial
temporal lobe structures have been linked to
both memory and spatial cognition,” said
Squire. One important aspect of spatial
cognition is keeping track of a reference
location during movement by using internal
cues, Squire explained, yet such tracking
also relies on memory.
“So we set out to test how
these two abilities related to one another
and to the temporal lobe area of the brain.”
The researchers looked at
five memory-impaired patients with lesions
of the medial temporal lobe along with seven
matched controls, testing each for their
path integration ability.
Participants, who were
blindfolded and wore noise-canceling
earphones, were led by researchers on 16
paths and asked to keep their starting point
in mind.
After walking the path,
participants were asked to point to their
start location.
Due to their lesions, the
five patients all had long-term memory
impairment, so the paths were short enough
that the task could be performed within the
span of their working, or short-term,
memory.
Building on the idea that
working memory is independent of the medial
temporal lobe, the researchers theorized
that these patients should succeed at the
task if performed within the span of their
short-term memory, unless this section of
the brain was also necessary for spatial
cognition.
The memory-impaired patients
pointed to and estimated their distance from
the start location as accurately as the
controls.
“We concluded that the
hippocampus and entorhinal cortex are not
essential for path integration, since we
showed that the tests could be successfully
accomplished despite damage to these brain
regions,” said Squire.
Co-authors Yael Shrager, UCSD
Department of Neurosciences, and C. Brock
Kirwan, UCSD Department of Psychiatry, also
contributed to this study, which was
supported by the Medical Research Service of
the Department of Veterans Affairs, the
National Institute of Mental Health, the
Metropolitan Life Foundation and a National
Science Foundation pre-doctoral fellowship.
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