The invention of functional magnetic resonance imaging (fMRI) nearly 30 years ago revolutionized neuroscience by letting researchers visualize brain activity associated with behavior. The technology is spatially precise, but its main limitation is speed; fMRI measures blood oxygen level changes, which take about six seconds—a snail's pace as compared with brain signals themselves. Other methods, such as electroencephalography (EEG), are fast but imprecise and cannot detect deeper brain signals.
Now physicists Samuel Patz of Harvard Medical School and Ralph Sinkus of King's College London and their colleagues have adapted existing tissue-imaging technology to overcome fMRI's speed limitation and tested it in mouse brains. Known as functional MR elastography (fMRE), it involves sending vibrations through tissue and using magnetic resonance to measure their speed. They move faster through stiffer material, producing “elastograms,” or maps of tissue rigidity, that may correspond to brain activity. This is the first time fMRE has been used to measure such activity, the researchers say.
In a study published in April in Science Advances, Patz, Sinkus and their colleagues applied mild shocks to mice's hind limbs to induce signals in the brain, turning the stimulation on and off at various rates. Comparing fMRE scans taken during on and off periods allowed them to produce images showing which areas changed in stiffness as a result of the stimulation. The researchers think certain brain cells soften when an associated neuron fires, meaning stiffness changes would correspond to neural activity. By varying the stimulation switching rate, they demonstrated that fMRE can detect brain signals at least every 100 milliseconds.
The team is currently testing the method in humans. “We've got very nice data now showing that it works,” Patz says. If everything pans out, the technique could represent an important advance in brain imaging. “We'd be in a much better position to conduct ‘effective connectivity’ analyses, where you try to figure out how information flows in brain circuits,” says neuroscientist Jonathan Roiser of University College London, who was not involved in the work.
Patz's colleague Alexandra Golby, a neurosurgeon, hopes to use fMRE to identify critical areas to avoid during brain surgeries. In about 30 percent of patients with tumors, the mass blocks the changes in blood oxygenation that fMRI measures, Patz says—“so [Golby] wanted a method that works differently.” The technique might ultimately help researchers understand and diagnose brain disorders involving circuit dysfunctions, such as schizophrenia. “It could reveal a lot of information that might be valuable for disease diagnosis [and] progression,” Patz says.
