17 October 2007
Blood Could Be Integral Part Of Brain's Processing Power
by Kate Melville
Scientists from the Massachusetts Institute of Technology believe that blood may actually 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," explained MIT's Christopher Moore. Writing in the Journal of Neurophysiology, he noted that many lines of evidence suggest that blood does something much more interesting than just delivering supplies. "If it does modulate how neurons relay signals, that changes how we think the brain works," he said.
According to Moore, blood is not just a physiological support system but actually helps control brain activity by changing blood flow and affecting the activity of nearby neurons. This changes how the neurons transmit signals to each other and hence regulates information flow throughout the brain.
The hypothesis has deep 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. "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."
Moore's theory also has important implications for functional magnetic resonance imaging (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," explained co-researcher Rosa Cao. "If blood flow shapes neural activity and behavior, then fMRI is actually imaging a key contributor to information processing."
Importantly, studies in Moore's lab support this interpretation. 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.
What mechanism allows blood flow to affect brain activity? Moore speculates that 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.
Moore says his 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. 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," he noted.
Source: Massachusetts Institute of Technology