How Your Brain Builds Sentences, Word By Word?

New research reveals the brain's hidden complexity in crafting sentences from simple words

Have you ever stopped to think about how we speak? Not just choosing the right word, but arranging those words into clear, meaningful sentences—often in a fraction of a second. This seemingly simple act is actually one of the most complex tasks your brain performs every day. For years, scientists have tried to understand how language is created inside our brains. Now, a groundbreaking study from New York University (NYU) is offering an exciting and detailed answer.

Led by Adeen Flinker, Associate Professor of Biomedical Engineering at NYU Tandon and Neurology at NYU Grossman School of Medicine, and Postdoctoral Researcher Adam Morgan, the research team used advanced brain-scanning tools to uncover how our brains transform single words into full sentences. And the results are mind-blowing.

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The Challenge: From Words to Sentences

Most previous research on how we produce language has focused on individual words—like asking someone to name an object in a picture. While this gives some insight into word recall, it doesn’t reflect how we really use language in everyday life. In real conversations, we don’t just speak words; we build sentences. This process is far more complicated and was not well understood—until now.

That’s what makes this new NYU study so important. Instead of looking only at isolated words, the researchers studied how the brain behaves when people speak full sentences. And what they found challenges some long-standing beliefs about how language works in the brain.

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The Method: Listening to the Brain in Real-Time

To explore sentence formation, the researchers worked with ten neurosurgical patients who were already undergoing brain surgery for epilepsy. These patients had electrodes placed directly on the surface of their brains—a process called electrocorticography (ECoG)—which allowed scientists to record brain activity in incredible detail and precision.

The patients were asked to complete two different language tasks:

1. Say single words (like “Frankenstein” or “hit”).

2. Describe simple cartoon scenes using full sentences (like “Frankenstein hit Dracula”).

By using machine learning, the team was able to track and decode how each individual word was processed in the brain. They then compared what changed—or didn’t change—when those same words were used in complete sentences.

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The Big Discovery: Brain Patterns Are Not All the Same

At first, the results showed something expected: the brain created unique and consistent activity patterns for each word when spoken on its own. This confirmed that the brain has a stable way of processing individual words, regardless of context.

But things became much more interesting when the words were used in full sentences. The patterns in some brain regions remained stable, but other regions—especially the prefrontal cortex—changed dramatically based on the sentence structure.

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Key Brain Areas Involved in Sentence Building

1. Sensorimotor Regions
   These areas followed the spoken words in the exact order they were said. So if someone said, “Frankenstein hit Dracula,” the brain lit up in sequence—first for “Frankenstein,” then “hit,” then “Dracula.” This region seems to act like a rhythm tracker, keeping pace with the flow of speech.

2. Prefrontal Cortex (Inferior and Middle Frontal Gyri)
   This is where things get complicated—and fascinating. These parts of the brain did not just follow word order. Instead, they analyzed the role each word played in the sentence. Was the word a subject or an object? Did it come first, or was it being acted upon?

   For example, in the sentence “Frankenstein hit Dracula,” the brain knew “Frankenstein” was the one doing the hitting, and “Dracula” was the one being hit. But even more impressively, in a sentence like “Frankenstein was hit by Dracula,” where the order is flipped, the brain still figured out who did what—even though it took more effort.

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Memory in Action: Holding Words Longer for Complex Sentences

The researchers noticed something incredible when participants used passive voice (like “Frankenstein was hit by Dracula”). In these cases, the prefrontal cortex kept both nouns active in the brain throughout the sentence. That means the brain was holding on to both “Frankenstein” and “Dracula” at the same time, even as the sentence unfolded.

This process, called sustained parallel encoding, shows that the brain doesn’t just read from a script. It actually stores and manipulates information in real time, adjusting based on the sentence’s complexity. In simple terms, the harder the sentence structure, the more brainpower needed.

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Why Word Order Matters: A Linguistic Insight

Here’s where it gets even more interesting: the study helps explain why most of the world’s languages follow a Subject-Verb-Object (SVO) pattern—like “I eat apples” instead of “Apples eat I.” According to the researchers, this preference may not be random. Instead, it could be a result of neural efficiency.

When people use non-standard sentence structures—like passive voice—the brain has to work harder, use more memory, and keep more elements active. Over time, evolution may have favored simpler sentence structures that require less mental effort. That’s why active sentences are more common and easier for the brain to process.

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Challenging Old Beliefs: Sentence Production Is Not Just Linear

Previously, many scientists believed that speaking was a fairly linear process: first pick the word, then say it, and repeat. But this new research shows that sentence production is more dynamic and flexible. Different parts of the brain handle different aspects of language—some keep track of word meaning, while others figure out how those words fit into grammar rules.

It’s not just about picking the right word—it’s about picking the right word for the right role in the sentence. The prefrontal cortex acts almost like a sentence planner, deciding how the sentence will come together before it even begins.

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Why This Research Matters

Understanding how the brain builds sentences is more than just an academic exercise. It could have major real-world benefits:

• Better treatments for speech disorders
  People with conditions like aphasia (difficulty speaking after a stroke) might benefit from therapies targeting specific brain regions involved in syntax and sentence planning.

• Smarter language technology
  Insights from this study could help improve AI language models and voice assistants by mimicking how the human brain structures speech.

• Deeper understanding of bilingualism and language learning
  Knowing how the brain manages grammar could make it easier to design tools and strategies for learning new languages more efficiently.

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Conclusion: A New Chapter in Language Science

This study represents a major step forward in our understanding of human language. By peering into the brain during sentence production, scientists have uncovered a flexible, layered, and efficient system that goes far beyond simply choosing words. Instead, our brains engage in a complex dance—balancing word meanings, roles, and grammar rules—all in real time.

The next time you speak a sentence, pause for a moment. Behind every word, there’s a sophisticated mental orchestra playing just for you. And thanks to this incredible research, we’re finally starting to hear the music.

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Key Takeaways:

• The brain uses different regions to handle word meanings and sentence structure.

• Sensorimotor areas follow the order of spoken words.

• The prefrontal cortex analyzes syntax, roles, and maintains information for complex sentences.

• Passive sentences require more brain effort than active ones.

• The study suggests that language structure preferences may have evolved for cognitive efficiency.

• Understanding these mechanisms can improve speech therapy, AI, and language education.

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Fun Fact:
The human brain can build and say over 100,000 different sentences a day—without even thinking about it. That’s the power of syntax on the brain!

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Reference: Adam M. Morgan et al, Decoding words during sentence production with ECoG reveals syntactic role encoding and structure-dependent temporal dynamics, Communications Psychology (2025). DOI: 10.1038/s44271-025-00270-1