Blood May Help Us Think
- From: carles <riqcarles@xxxxxxxxx>
- Date: Sat, 27 Oct 2007 01:09:36 -0000
ScienceDaily (Oct., 2007)
MIT scientists propose that blood may help us think, in addition to
its well-known role as the conveyor of fuel and oxygen to brain
cells.
We hypothesize that blood actively modulates how neurons process
information," explains Christopher Moore, a principle investigator in
the McGovern Institute for Brain Research at MIT, in an invited review
in the Journal of Neurophysiology. "Many lines of evidence suggest
that blood does something more interesting than just delivering
supplies. If it does modulate how neurons relay signals, that changes
how we think the brain works."
According to Moore's Hemo-Neural Hypothesis, blood is not just a
physiological support system but actually helps control brain
activity. Specifically, localized changes in blood flow affect the
activity of nearby neurons, changing how they transmit signals to each
other and hence regulating information flow throughout the brain.
Ongoing studies in Moore's laboratory support this view, showing that
blood flow does modulate individual neurons.
Moore's theory has implications for understanding brain diseases such
as Alzheimer's, schizophrenia, multiple sclerosis and epilepsy. "Many
neurological and psychiatric diseases have associated changes in the
vasculature," says Moore, who is also an assistant professor in MIT's
Department of Brain and Cognitive Sciences.
"Most people assume the symptoms of these diseases are a secondary
consequence of damage to the neurons. But we propose that they may
also be a causative factor in the disease process, and that insight
suggests entirely new treatments." For example, in epilepsy people
often have abnormal blood vessels in the brain region where the
seizures occur, and the hypothesis suggests this abnormal flow may
induce epileptic onset. If so, drugs that affect blood flow may
provide an alternative to current therapies.
The hypothesis also has important implications for functional magnetic
resonance imaging, or fMRI, a widely used brain scanning method that
indicates local changes in blood flow. "Scientists looking at fMRI
currently regard blood flow and volume changes as a secondary process
that only provides read-out of neural activity," explains Rosa Cao, a
graduate student in Moore's lab and co-author of the paper. "If blood
flow shapes neural activity and behavior, then fMRI is actually
imaging a key contributor to information processing."
Again, studies in Moore's lab support this interpretation. For
example, his fMRI studies of the sensory homunculus - the brain's
detailed map of body parts like fingers, toes, arms, and legs- show
that when more blood flows to the area representing the fingertip,
people more readily perceive a light tap on the finger. This suggests
that blood affects the function of this brain region and that
information about blood flow can predict future brain activity. This
finding does not undermine prior studies, but adds another, richer
layer to their interpretation and makes fMRI an even more useful tool
than it already is.
How could blood flow affect brain activity? Blood contains diffusible
factors that could leak out of vessels to affect neural activity, and
changes to blood volume could affect the concentration of these
factors. Also, neurons and support cells called glia may react to the
mechanical forces of blood vessels expanding and contracting. In
addition, blood influences the temperature of brain tissue, which
affects neural activity.
To Moore's knowledge, the Hemo-Neural Hypothesis offers an entirely
new way of looking at the brain. "No one ever includes blood flow in
models of information processing in the brain," he asserts. One
historical exception is the philosopher Aristotle, who thought the
circulatory system was responsible for thoughts and emotions. Perhaps
the ancient Greeks were on to something.
This work was funded by Thomas F. Peterson, the Mitsui Foundation and
the McGovern Institute for Brain Research at MIT.
Adapted from materials provided by Massachusetts Institute of
Technology.
GIDEM
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