[tt] PhysOrg: First look: Princeton researchers peek into deepest recesses ofhuman brain

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First look: Princeton researchers peek into deepest recesses of
human brain
http://www.physorg.com/printnews.php?newsid=123346944

A team of scientists from Princeton University has devised a new
experimental technique that produces some of the best functional
images ever taken of the human brainstem, the most primitive area of
the brain.
The scientists believe they may be opening the door to inquiries
into a region that acts as the staging area for the brain chemicals
whose overabundance or absence in other parts of the brain are at
the root of many neuropsychiatric disorders, like addiction,
schizophrenia and Parkinson's disease.
Reporting in the Feb. 28 edition of Science, the scientists describe
using functional magnetic resonance imaging to study brainstem
activity in dehydrated humans. The scanning technique allows
researchers to watch the brain in action.
The subjects were participating in classical conditioning
experiments in which they were presented with a visual clue, then,
at varying intervals, given a drink. The researchers were able to
track changes in blood flow in areas of the brainstem associated
with enhanced activity of the brain chemical dopamine -- as the
person experienced either pleasure or disappointment at receiving or
not receiving the reward.
"For a long time, scientists have tried looking at this area of the
brain and have been unsuccessful -- it's just too small," said
Kimberlee D'Ardenne, the lead author on the paper. Until now,
scientists wanting to use brain scans to study brain chemicals like
dopamine were relegated to watching its effects in other more
accessible parts of the brain, like the prefrontal cortex and
ventral striatum. However, this was downstream of its source, and
therefore possibly much less accurate, D'Ardenne said.
"We wanted to try because the brainstem is so important to
activities in the rest of the brain," said D'Ardenne, a postdoctoral
student in the Department of Chemistry. "We believe it could be a
key to understanding all kinds of important behavior."
For the research, D'Ardenne collaborated with Jonathan Cohen,
co-director of the Princeton Neuroscience Institute, and Samuel
McClure and Leigh Nystrom, other institute scientists. They
conducted the studies on the University's own brain scanner located
on campus in Green Hall.
Cohen noted that these findings provide a critical link between
studies in non-human animals that have looked directly at the
activity of dopamine cells in the brainstem and studies in humans of
behaviors thought to be related to dopamine. "It could also open up
entirely new avenues of study," he said.
The team was able to develop high-resolution images that tracked the
activity of tiny clusters of dopamine neurons. They weeded out
distortions caused by many pulsing blood vessels in the brainstem.
They also employed computerized rules of thumb known as algorithms
and imaging techniques to reduce the effects of head movement and
combine images from different subjects.
The MRI device produces three-dimensional images that show what
portions of the brain engage during actions and thought processes.
This allows the investigators to correlate physical processes with
mental activities with unprecedented precision.
The brain stem, a tiny, root-shaped structure, is the lower part of
the brain and sits atop the spinal cord. The area controls brain
functions necessary for survival, such as breathing, digestion,
heart rate, blood pressure and arousal. The brain structure also
serves as the home base for the brain chemicals, also known as
neuromodulators, such as dopamine, serotonin and norepinephrine. The
chemicals spring forth into other brain regions from there, zipping
along routes called axons.
The team's experiments confirmed results already seen in animal
studies. Blood flow increased in dopamine centers of the brainstem
when test subjects were happily surprised with a reward. However,
there was no activity when participants received less than what they
expected, a finding that is different from the results of previous
studies looking farther downstream.
"We are just at the beginning of understanding these crucial
pathways," D'Ardenne said. "But it gives us a hint about what is
possible to know."
The tiny clumps of cells containing neuromodulator chemicals in the
brainstem, called nuclei, have long been known to play a critical
role in the regulation of brain function, and disturbances of these
systems have been implicated in most psychiatric disorders, from
addiction to schizophrenia, D'Ardenne said.
The Princeton group wants to understand how the brain's physical
structures give rise to the functions of the mind, a field known as
cognitive neuroscience.
For years, neuroscientists focused on the brain while psychologists
dealt with the mind. The new field combines both and is being
powered by scientific advances in brain imaging and gene
manipulation that allows researchers to record and measure the
activity of brain cells as humans or animals perform mental tasks.

Source: Princeton University