[tt] Blood may help us think | Science Blog

[Brian Atkins]

http://www.scienceblog.com/cms/blood-may-help-us-think-14531.html

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.

-- 
Brian Atkins
Singularity Institute for Artificial Intelligence
http://www.singinst.org/