New Hypothesis for Blood's Role in Cognition
> 1/25/2008 2:38:21 PM

Many cognitive problems have been linked to abnormal blood-flow to the brain. Vascular dementia, for example, has been tied to a variety of blood-flow problems. The common assumption has been that blood-flow is only important to the brain for the nutrients that it brings. Neurons require massive amounts of oxygen in particular to function optimally. While it is indisputable that neurons do rely on these nutrients, an interesting new hypothesis about an additional role for blood, put forth by Christopher Moore from MIT, has been gaining traction.  
Moore's Hemo-Neural Hypothesis, originally published in the Journal of Neurophysiology, posits that blood actually serves a computational purpose in addition to providing raw supplies. This is not as out-there as it might look at first. Edith Hamel, an unaffiliated professor who sees great promise in the hypothesis, explained to Scientific American why blood should not be overlooked:

A lot of people have been ignoring—thinking that blood vessels are tubes. But, they are live cells…like neurons.

One reason that Moore felt the drive to create his hypothesis is a discrepancy noticed since the fMRI first came into use. The fMRI assumes that neural activity can be indirectly measured by monitoring the blood flow carrying nutrients to neurons. While there is certainly a correlation, blood flow seems to increase far more than is necessary; an activation increase of 4% corresponds to a blood-flow increase of approximately 40%. While some have tried to explain this away by saying that higher flows are inefficient and thus require more volume for the same gain, many others remain puzzled by this seeming waste.

Moore points out that there are many ways that blood might interact with neurons to perform cognitive functions. Changes in temperature and pressure can modulate neural activity, as can many substances in blood such as nitric oxide. While Moore's laboratory work is a long way from offering conclusive evidence, Scientific American reports that his early work has thus far supported the idea that blood directly and rapidly changes the activation of neurons.

If the Hemo-Neural Hypothesis proves correct, then we will have to change the way that we think about many neural disorders, as well as the way that we interpret fMRI results. The idea that humans only use 10% of their brains is a myth. Our bodies are amazingly well-constructed, and they rarely waste energy or space. It may very well turn out that we have been ignoring an important mechanism for cognition.

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