The brain’s language network is more extensive than previously thought

For decades, neuroscientists have known that specific regions in the brain's left hemisphere are responsible for processing language. However, a new study by MIT researchers shows that language processing also occurs in many other parts of the brain.

Using functional magnetic resonance imaging (fMRI) data from more than 700 people, the researchers identified 17 additional regions of the brain that appear to play a role in language. These regions are scattered across the brain, including parts of the cerebellum, hippocampus, and cerebral cortex, and they make up about 5 percent of the total volume of the adult brain - about the size of a large strawberry.

"Even though there are all these distant components, it's pretty restricted in terms of volume. You don't need that much of the brain to do language," says Evelina Fedorenko, an MIT associate professor of brain and cognitive sciences, a member of MIT's McGovern Institute for Brain Research,and the senior author of the study.

Exactly how these regions contribute to language processing is still to be discovered, although the researchers have made some progress toward determining the functions of the cerebellar regions that they identified.

MIT postdoc Agata Wolna is the lead author of the paper, which appears in the Journal of Neuroscience. Other authors include Aaron Wright, a K. Lisa Yang Post-Baccalaureate Research Scholar at MIT; Colton Casto, a graduate student at Harvard University; Samuel Hutchinson, a graduate student at MIT; and Benjamin Lipkin PhD '26.

Tracking language

The brain's language processing centers include Broca's area, first discovered in the 1800s, plus additional regions in the left frontal and temporal lobes of the brain. Scientists have found that some of the corresponding areas of the right hemisphere also contribute to processing language, especially the social-emotional components of language.

There have also been hints that other parts of the brain might be involved in language processing. Early in her career, Fedorenko's language studies often showed active brain regions outside of the canonical language centers, but she says she was discouraged from including them in her papers.

"When we initially started looking at language, in the first couple of papers, I tried to be comprehensive and include anything that seemed consistent across participants, and there was a huge amount of resistance," she says. "People would say things like, 'Well, we know those are not language areas, so please focus on the language areas.'"

In the new study, she and Wolna wanted to revisit those brain scans and see if they could systematically identify language regions outside of the standard language-processing areas.

To do that, they analyzed data from 772 people who had been scanned in Fedorenko's lab since 2013. Each of these participants underwent a task known as a language localizer, which is used to determine the location of language processing areas for each subject.

During the test, participants read or listen to sentences as well as sequences of nonwords. For each person, the researchers measure the difference in strength of response when reading real sentences or nonsense sequences. The brain areas that work harder during the sentence condition are considered to be doing something relevant to language, especially if they respond while both reading and listening to sentences.

"It's a very simple paradigm that lets you identify this core language system in individual brains," Wolna says.

When searching for language areas, the researchers usually use a relatively strict statistical threshold. In this study, they relaxed the threshold and also used some targeted searches in subcortical areas, in hopes of finding all areas that may contribute to language processing."We always see this frontal temporal network, but there's quite a lot of evidence that there are other regions that are also critical for language processing," Wolna says. "By using a laxer threshold and zooming in on areas with weak MRI signal, we tried to maximize the chances of finding small and weakly responsive regions outside of this left frontal temporal system."

A widespread network

For about 490 of the participants, the researchers also had data on how their brain responded during a spatial working memory task - remembering the locations of flashing squares on a grid. This task engages a brain network called the multiple demand system, which does not overlap with the core language areas.

This task allowed the researchers to ask whether any of the newly identified language-sensitive regions specifically respond to language and not more general cognitive processes.

Of the 17 new language sites that were revealed by this study, five are located in the cerebellum, which is mainly involved in coordinating the body's movement. In a study published earlier this year, researchers led by Casto found that three of those cerebellar regions also became engaged during some nonlinguistic cognitive tasks, which was also seen in the new study.

"Those areas that respond to both language and some other tasks could be really interesting and important because they may be doing something like integrating information from different cortical systems," Fedorenko says.

They also found language-selective regions in the medial frontal cortex, the bottom surface of the left temporal lobe, the hippocampus, and the amygdala. The researchers now plan to further study how these brain regions might contribute to language processing.

"We can now test some ideas from past work, and also more rigorously characterize these regions across different kinds of language manipulations, and different kinds of nonlinguistic tasks, to try to understand what it is that they're doing," Fedorenko says.

The research was funded by the Simons Center for the Social Brain at MIT, the McGovern Institute, MIT's Department of Brain and Cognitive Sciences, and the MIT Siegel Family Quest for Intelligence.