Researchers from the University of Illinois Urbana-Champaign, working with domestic and international collaborators, have combined three imaging techniques to detect the timing and location of brain responses to a stimulus. The researchers said the study is the first to combine the three technologies for simultaneous imaging of brain activity.
The trimodal approach combines EROS (event-related optical signal), a technique that tracks the activity of neurons near the surface of the brain using near-infrared light; functional MRI (fMRI); and electroencephalography (EEG).
A new approach to brain imaging combines functional MRI, electroencephalography, and a technique known as EROS, which shines near-infrared light on the scalp to capture brain activity. Courtesy of University of Illinois.
“We know that fMRI is very good at telling us where in the brain things are happening, but the signal is quite slow,” postdoctoral researcher Matthew Moore said. “And when we measure electrical activity through EEG, it is very good at telling us when things happen in the brain — but it’s less precise about where.”
EROS provides a measure of spatial information similar to fMRI, but, like EEG, it can more accurately assess the timing of brain responses. This helps researchers fill in the blanks left by the other two technologies, Moore said. The result is a clearer picture of how different parts of the brain are activated and communicate with one another when an individual engages in a cognitive task and is distracted — in this case by emotionally challenging information.
fMRI captures a signal from the flow of oxygenated blood in the brain when a person sees or responds to a stimulus. This signal is useful in determining which brain structures are being activated, Moore said.
“Changes in blood oxygenation levels occur over a period of seconds, but the brain actually responds within hundreds of milliseconds,” Moore said. The lag between brain activity and oxygenation signals means that fMRI is unable to detect changes occurring faster than seconds.
“On the other hand, EEG is very good at telling us when things happen,” Moore said. “But we’re collecting from sensors placed on the scalp, and we’re getting a summation of activity, so really, we’re blurring across centimeters of the scalp.”
EROS was developed by two co-authors of the current work, University of Illinois psychology professors Monica Fabiani and Gabriele Gratton. The method shines near-infrared light into the brain and measures changes in how the light scatters, a reflection of neural activity. EROS provides precise information about when and where the brain responds, though it can only penetrate a few centimeters below the scalp, so it is unable to detect events happening deeper within the brain, as fMRI can, the researchers said.
Due to limited space available on the scalp for various electrodes and sensors, and the need for the EEG and EROS equipment to fit within an fMRI coil and not contain any magnetic metals, the researchers had to find a way to include EROS patches that could share space with EEG electrodes on the scalp. They tested different combinations of the three techniques to determine how to connect them and how to interpret the information coming through the different channels.
To study how the brain behaves when a person tries to focus on a task but is distracted by emotional information, the researchers gave study participants a goal of quickly picking out circles from a series of squares and other images that had either emotionally neutral or negative context.
The imaging results showed that various brain regions responded rapidly to the stimuli. The signals cycled back and forth between locations over the prefrontal and parietal cortices — brain regions that work together to maintain attention and process distractions. This switching occurred on a timescale of hundreds of milliseconds, the researchers found.
Switching attention from a distraction to get back on task is highly relevant to normal cognitive function, said study leader Florin Dolcos, a professor of psychology at Illinois who studies emotional gelation and cognition.
“Sometimes people with depression or anxiety are not able to switch away from emotional distractions and focus,” he said. “Better imaging studies will make it easier to test individuals who have been trained in specific emotion-regulating strategies to see if those strategies are working to improve their cognition. And now we can image this with precision in real time, at the mind’s speed.”
University of Illinois funders that supported the work include the Campus Research Board, the psychology department, and the Beckman Institute.
The research was published in Human Brain Mapping (www.doi.org/10.1002/hbm.25541).