Washington, Dec 4: Scientists have for the first time successfully tracked human thought by imaging rapidly fluctuating brain activity using fast fMRI. Functional magnetic resonance imaging (fMRI) measures changes in blood oxygenation, which were previously thought to be too slow to detect the subtle neuronal activity associated with higher order brain functions.
The new discovery that fast fMRI can detect rapid brain oscillations is a significant step towards realising a central goal of neuroscience research: mapping the brain networks responsible for human cognitive functions such as perception, attention, and awareness.
“This work demonstrates the potential of fMRI for mapping healthy neural networks as well as those that may contribute to neurological diseases such as dementia and other mental health disorders, which are significant national and global health problems,” said Guoying Liu from the US National Institute of Biomedical Imaging and Bioengineering (NIBIB).
The fMRI works by detecting local increases in oxygen as blood is delivered to a working part of the brain. The technique has been instrumental for identifying which areas in the brain control functions such as vision, hearing, or touch. However, standard fMRI can only detect the blood flow coming to replenish an area of the brain several seconds after it has performed a function.
It was generally accepted that this was the limit of what could be detected by fMRI – identification of a region in the brain that had responded to a large stimulus, such as a continuous 30 second “blast” of bright light. Combining several new techniques, researchers applied fast fMRI in an effort to track neuronal networks that control human thought processes, and found that they could now measure rapidly oscillating brain activity.
The researchers used fast fMRI in human volunteers observing a rapidly fluctuating checkerboard pattern. The fast fMRI was able to detect the subtle and very rapid oscillations in cerebral blood flow in the brain’s visual cortex as the volunteers observed the changing pattern.
“The oscillating checkerboard pattern is a more “naturalistic” stimulus, in that its timing is similar to the very subtle neural oscillations made during normal thought processes,” said Jonathan R Polimeni of Massachusetts General Hospital in the US. “The fast fMRI detects the induced neural oscillations that allow the brain to understand what the eye is observing – the changing checkerboard pattern,” said Polimeni.
“These subtle oscillations were completely undetectable with standard fMRI. This exciting result opens the possibility of using fast fMRI to image neural networks as they guide the process of human thought,” he said. The study was published in the journal PNAS.