FOR IMMEDIATE RELEASE: 27 JANUARY 1999
Contact: Gary Dorsey
[log in to unmask]
410-516-7160
Johns Hopkins University
New Clues To Evolution Of Human Brain
In her quest to examine the contents of consciousness, a scientist
at The Johns Hopkins University has produced new evidence of the
evolutionary path from the monkey brain to the human.
Susan Courtney, an assistant professor of psychology, recently
reported that she had pinpointed the place where the human brain
stockpiles information about spatial relationships for short-term use.
It was not where anyone expected.
Until recently, many scientists argued that storage depots for
short-term memory (called "working memory") in humans were probably
located in the same place as in monkeys; memory of spatial relationships
was thought to be stored in the top half of the frontal cortex and
memory of objects was stored in the bottom half.
But using a relatively new brain-mapping technology called
functional magnetic resonance imaging (fMRI*), Courtney discovered that
the human brain has a dedicated place for spatial working memory located
further back in the brain anatomy.
"Until now, it's been rather controversial," Courtney said,
"because people have based their theories about human brain physiology
on what they have seen in non-human primates. And yet when scientists
went looking for a particular place for spatial working memory in
humans, they couldn't find it. But now, with the help of new
technologies such as fMRI, we can see where the human brain handles some
of its short-term storage."
"The difference has interesting implications for human brain
evolution," Courtney said.
"The comparison indicates that there has been a great expansion of
the frontal cortex in the evolution from monkeys to humans, pushing this
older area, reserved for spatial memory, out of the way," she said. "Of
course, one of the big questions is what replaced it. From the imaging
work and from studies of people with damage to that part of the brain,
it looks as if these 'new' areas are involved in functions that are, if
not uniquely human, then greatly more developed in humans -- for
example, abstract reasoning, planning for the future, and manipulation
of information."
In the past, researchers who wanted detailed studies of human brain
activity struggled because they lacked effective investigative tools. In
experiments with people, two of the best technologies brought only
limited success in mapping the processes of consciousness. An EEG
(electroencephalogram), for example, could not pinpoint where brain
signals were coming from, and PET (positron emissions tomography)
required radioactive tracers, which limited the exposure times of
subjects. PET was also restricted because it could only provide an image
of brain activity integrated over a minute or two.
Consequently, researchers have relied on monkeys who have undergone
invasive surgery and the
implantation of electrodes into the brain for monitoring biological
activity. For that reason, the primate brain has served as the model for
understanding some of the finer aspects of human brain performance.
Functional MRI, however, can be used repeatedly on human subjects
without causing harm or relying on invasive procedures. Plus, the
resolution is so good that scientists like Courtney can observe changes
in the brain every few seconds, allowing them to chart neural activity
nearly in real time.
For Courtney, who is discretely examining what she calls "the
contents of consciousness," functional imaging has advanced her work
considerably. Besides revealing clues about human brain evolution, her
latest work with functional imaging also revealed that the process of
retrieving short-term memories of faces shares the same physical
mechanism in the brain as that for retrieving long-term memories of
faces -- forcing yet another wedge into the mysteries of consciousness.
"It's great uncharted territory," she said. "But we're beginning to
make a lot of progress."
Her work was funded by the National Institute of Mental Health and
reported in the Philosophical Transactions of the Royal Society of
London.
(* Functional magnetic resonance imaging (fMRI) is based on the
fact that neural activity causes an increase in blood flow, which in
turn increases blood oxygenation. The technology maps the brain by
charting the relative increase in oxygenated hemoglobin while
researchers conduct various experiments on their subjects that may, for
example, task memory or test senses.)
###
--
Judith Richards, London, Ontario, Canada
<[log in to unmask]>
^^^
\ /
\ | / Today’s Research
\\ | // ...Tomorrow’s Cure
\ | /
\|/
```````
