Local scientists are honing a new technique to study brain activity in infants.

Constanza Villalba

Infancy is a time of tremendous change in the brain. Connections between neurons form and break, nerve cells branch and extend to form networks, and parts of the brain become specialized for vision, language, and other complex tasks. Many of these processes have “critical periods”—narrow windows of time during which they take place. What’s more, these processes sometimes go awry, leading to learning disabilities, language impairments, and other deficits.

For these reasons and many others, neuroscientists hunger for tools with which to study the brain and its activity as it develops during infancy. Electroencephalography (EEG) and related techniques that measure the brain’s electrical signals have been the mainstay for this work, because they are safe to use on babies and because they register changes very quickly. While these techniques measure neuronal activity, they cannot reliably pinpoint where in the brain that activity originates.

Another technique, functional magnetic resonance imaging (fMRI), is better at locating activity within the brain. However, fMRI is challenging and possibly even dangerous to use on babies, because it requires that the babies hold still and exposes them to strong magnetic fields.

Now, with the help of Heather Bortfeld of Texas A&M University and David Boas of Massachusetts General Hospital, developmental neuroscientists are perfecting another imaging tool to study brain activity in infants. The technique, called near-infrared spectroscopy (NIRS), offers the prospect of a tool that can locate activity in the brain the way fMRI can—without having to restrain the baby or put it inside an MRI machine.

“We can study real, live interactions, looking at the behavior of [freely-moving] subjects,” says Boas. “That’s something you can’t do with fMRI.”

The NIRS imaging apparatus uses a varying number of light-emitting diodes and light-sensing detectors, which are usually affixed to a cap or a headband. The diodes emit near-infrared light, which passes through skin and bone and penetrates into the brain. The detectors measure the intensity of the light that reflects back.

Researchers measure brain activity by looking for signs of increased blood oxygen levels; an active part of the brain has higher concentrations of oxygenated hemoglobin in blood. Because oxygenated hemoglobin in blood absorbs near-infrared light differently than deoxygenated hemoglobin, the light signal changes when reflected back from an active region of the brain.

NIRS has been used clinically for several years to monitor cerebral blood flow in premature babies. Only recently have researchers begun using the technology to monitor brain activity during specific cognitive or sensory tasks in full-term, healthy babies. One notable paper on the topic, authored by Bortfeld and Boas, is in press with the journal Neuroimage.

For this study, parents sat holding their infants in front of a computer screen. As the babies watched, the screen went from being blank to displaying slow-moving, three-dimensional objects, to showing the objects while playing a recording of animated speech.

According to the NIRS readings, when the babies saw the moving shapes, the part of the brain thought to be responsible for vision became activated. When they saw the moving shapes and heard the speech, the part of the brain thought to be responsible for language comprehension also lit up.

While these findings are not surprising given what is already known about the brain areas in question, the study is important because it’s another proof-of-concept, demonstrating that NIRS can be used to measure brain activity associated with cognitive tasks, says Richard Aslin, director of the Rochester Center for Brain Imaging at the University of Rochester.

He adds that Boas and his colleagues were able to avoid getting spurious signals when the infants moved, something other neuroscientists have had trouble doing with NIRS.

So far, NIRS cannot give as fleshed-out an anatomical picture as fMRI. But that may change as scientists develop ways to increase the number of diodes and detectors in NIRS devices. What’s more, the technique works in infants and adults alike, so scientists may be able to use it to compare people at different developmental stages.