National Institute of Mental Health (NIMH) scientists have pinpointed the
part of the human brain that holds information momentarily about where
things are located. This specialized circuitry for spatial working memory
keeps track of, for example, the ever-changing locations of other cars while
The discovery ends a search that had puzzled neuroscientists for most of the
past decade. "Some researchers were looking for this circuit in the same
area where it is in the monkey brain, but it appears to have been displaced
rearward and upward through evolution as areas serving more distinctly human
functions emerged," said NIMH's James Haxby, Ph.D. He, along with Susan
Courtney, Ph.D., and colleagues, report on their functional magnetic
resonance imaging (fMRI) study in the February 27 Science.
While other researchers focused on the human anatomical counterpart to the
area in the monkey, a region in the middle of the frontal cortex, the NIMH
team took their clue from a functional landmark. They hypothesized that, as
in the monkey, they would find the human spatial working memory circuits
just in front of an area specialized for controlling eye movements (frontal
eye field). They knew from brain imaging studies that this circuitry had
evolved into a higher and more rearward location in the human frontal cortex.
To confirm their hunch, they scanned a total of 11 subjects while they
performed various working memory and control tasks. The fMRI scanner tracks
telltale signals emitted by oxygenated blood in a magnetic field to reveal
what parts of the brain are active at any given moment.
While in the scanner, subjects were asked to remember either the locations
or the identities of three faces flashed briefly in different spots on a
computer screen. After a nine-second pause, during which the information
was held in working memory, a face appeared somewhere on the screen for a
few seconds. For the spatial working memory task, subjects pressed buttons
to indicate whether this latter location was the same as one of the three
they had seen previously. In trials testing non-spatial working memory, they
similarly signaled whether the identity of the "test" face was the same as
one of the three they had previously seen.
As hypothesized, the researchers saw high activity during an eye movement
task in the middle upper part of the frontal cortex, confirming location of
the frontal eye field. Also as predicted, just in front of this area they
discovered a heretofore unknown, functionally distinct, region that showed
sustained activity during the pause in the spatial working memory task,
confirming that it harbors the circuits for that function. A region in the
lower left frontal cortex showed sustained activation during the pause in
the face working memory task, thus clearly differentiating itself from the
spatial working memory area.
"As the human frontal cortex evolved, the circuitry for spatial working
memory appears to have been displaced to accommodate the emergence of newer
areas that mediate cognitive abilities, such as abstract reasoning, complex
problem solving and planning for the future," said Haxby.
These uniquely human abilities, as well as working memory, are impaired in
some severe mental disorders, such as schizophrenia.
"Working memory is an essential building block of our cognitive abilities,
from mental arithmetic to logical reasoning," said Leslie Ungerleider,
Ph.D., chief of the NIMH Laboratory of Brain and Cognition, which conducted
the study. "Working memory -- what we're aware of from one moment to the
next -- bridges time and is the content of our consciousness."
Also participating in the study were: Laurent Petit, Ph.D., and Jose Ma.
Maisog, M.D., of the NIMH.
NIMH is a component of the National Institutes of Health, an agency of the
U.S. Department of Health and Human Services.
View comparison of monkey and human brain