Key takeaways
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Spatiotemporally distributed frontotemporal networks for sentence reading.
Meaning
The human language network is represented through the frontal and temporal cortices. It is unclear whether subregions of this network contribute differently to sentence comprehension. We monitored the neural activity of patients implanted with intracranial electrodes while they read regular sentences and sentences deficient in meaning or structure. We discovered two functionally distinct networks spanning the frontotemporal cortex. The activity of the first network increased progressively in sentences, but not in word lists, indexing the accumulation of meaning in sentences. The second network showed reduced activity for words in sentences relative to word lists, suggesting that sentence context facilitates the processing of individual words. Our study exposes previously unknown organizational principles of the linguistic network,
Summary
Reading a sentence involves integrating the meanings of individual words to infer more complex, higher-order meanings. This highly rapid and complex human behavior is known to involve the inferior frontal gyrus (IFG) and the middle temporal gyrus (MTG) in the language-dominant hemisphere, but it is still unclear whether there are distinct contributions of these regions to sentence reading. . To test these neural spatiotemporal dynamics, we used direct intracranial recordings to measure neural activity when reading sentences, meaning-deficient Jabberwocky sentences, and lists of words or pseudowords .
We isolated two functionally and spatiotemporally distinct frontotemporal networks, each sensitive to different aspects of word and sentence composition. The first distributed network involves the inferior frontal gyrus (IFG) and the middle temporal gyrus (MTG), and IFG activity precedes MTG. Activity in this network increases during the duration of a sentence and is reduced or absent during Jabberwocky and word lists, implicating its role in deriving sentence-level meaning. The second network involves the superior temporal gyrus and IFG, with temporal responses leading those of the frontal lobe, and shows greater activation for each word in a list than in sentences, suggesting that sentence context allows for greater efficiency in the lexical and/or phonological. processing of individual words. These results imply distributed dynamic computation across the frontotemporal language network rather than a clear dichotomy between the contributions of frontal and temporal structures.
Comments
Reading is essential, but it is also a complex skill. Now, a new study sheds more light on how the brain makes sense of the written word. Researchers found that two key brain "networks" work together to help people read sentences, so that people not only grasp the meanings of individual words, but also process the big picture of what is being said.
Because reading is such an essential daily activity, it’s easy to take it for granted, said study leader Oscar Woolnough, a researcher at the McGovern School of Medicine at UTHealth Houston. "That is, until you lose that ability," he said. Woolnough pointed to the example of aphasia , which affects people’s ability to use language, including speech and the ability to write or read. It comes from damage to the brain, often from a stroke or head injury.
If researchers can better understand how the healthy brain allows people to read, Woolnough said, that could improve understanding of aphasia and other types of reading problems. For the most recent study, researchers recruited epilepsy patients who had electrodes implanted in their brains to try to identify the source of their seizures.
That allowed Woolnough’s team to record participants’ brain activity as they read, precisely mapping the timing of events in a way that is not possible with non-invasive brain imaging. The researchers had the 36 participants silently read several sentences and word lists, some composed of real words and others composed of meaningless "Jabberwocky" words (based on the poem "Jabberwocky" by Lewis Carroll ).
It turned out that when people read real sentences , two distinct networks in the brain’s frontotemporal cortex sprang into action. In the first, activity increased progressively as readers absorbed the sentences, an increase not seen when people read a list of words. That, Woolnough explained, suggests that the network is adding up the combined meaning of individual words in a sentence and building a larger picture of what is being said.
The second network the researchers identified worked differently: It was more active when people read lists of words , rather than sentences. But that’s not because he was lazy during the prayer reading. As Woolnough explained, the second network appears to become more efficient when people read sentences, because the context of the sentence makes it easier to process the individual words. "Your brain can start to predict what’s coming next," she said.
The findings, recently published in the Proceedings of the National Academy of Sciences , may not have immediate implications for addressing reading disorders. But experts said the study highlights the complexity of a task that is vital to everyday life. Reading ability cannot be identified in any center of the brain, said Monica McQuaid, director of the adult literacy program at the Fisher Landau Center for the Treatment of Learning Disabilities at Montefiore Medical Center in Bronx, New York. Instead, it involves an orchestration of the activity of various areas of the brain.
Dyslexia , for example , is sometimes misunderstood as a disorder in which people see words "backwards ," McQuaid said. But the problem is not visual , she explained. It is one of language processing . So addressing dyslexia requires a "multisensory" approach , McQuaid explained. Instead of, for example, simply showing a child the word "cat ," a therapist may also use a picture of a cat, the recorded sound of a cat, or integrate the movement of a cat, to "construct meaning . "
When it comes to aphasia , people often think it’s a speech problem, said Sarah Wallace, a professor of communication sciences and disorders at the University of Pittsburgh. In reality, she said, aphasia affects all language processing: speaking, writing and reading . Like McQuaid, Wallace noted the variety of brain areas involved in reading and the need for "multifaceted" approaches to managing deficits.
There are therapies to help people with aphasia improve their reading skills, usually with reading aloud. At the same time, Wallace said, it’s also important to make the task easier: Technology is one way to help, with text-to-speech devices that present written text and computerized speech at the same time, for example.
However, technology has also made everyone more reliant on reading, Wallace said. Emails and text messages have replaced the old phone calls. “Reading is such an important part of our everyday lives,” Wallace said. "It’s part of how we make new relationships and maintain them." Therefore, it is "critically important," he said, to better understand such a fundamental human skill.
