The blood that flows into our heads is obviously important for it provides nutrients and oxygen to that most energetically demanding of organs – the brain. But for neuroscientists, blood flow in the brain has a special significance; many have used it to measure brain activity using a technique called functional magnetic resonance imaging, or fMRI.
This scanning technology has become a common feature of modern neuroscience studies, where it’s used to follow firing neurons and to identify parts of the brain that are active during common mental tasks. Its use rests on the assumption that the flow of blood (“haemodynamics” to those in the know) is a decent enough stand-in for the firing of neurons – the latter creates a shortage of nutrients and oxygen that is corrected by the former.
But Yevgeniy Sirotin and Aniruddha Das from Columbia University have found that this assumption might not be entirely valid. They used a new technique to independently measure and compare nerve activity and blood flow in the brains of live monkeys. Sure enough, they found a blood flow pattern that reliably matched the activity of the animals’ neurons.
But they also spotted something that no one has seen before – a second haemodynamic signal, of equal strength to the first, that didn’t correspond to any local brain activity. This second signal was not a sign of parts of the brain that are active, but those that may need to be active in the near future. It seems that if the brain expects a task in the future, it can anticipate which of its regions will be needed and flush them with blood in preparation.