A single word can overturn your understanding of a sentence, and your brain chemistry may shape how hard you work to make sense of it again.
Even a single word can change the meaning of an entire sentence, forcing the brain to rethink what it just read. But how efficiently the brain handles these grammatical surprises may depend partly on its chemistry.
A study published in PNAS found that increasing dopamine and noradrenaline (catecholamines) strengthened a brain response associated with untangling ambiguous grammar. Researchers led by the Max Planck Institute for Psycholinguistics (MPI-PL) in Nijmegen observed the largest effects in healthy adults with lower baseline working memory capacity.
“Catecholamines are known to regulate attention, working memory, and cognitive control, but their role in language remains poorly understood,” says Peter Hagoort, senior investigator and director emeritus of MPI-PL’s Neurobiology of Language Department and the Donders Institute for Brain, Cognition and Behavior.
“Our earlier work suggested that catecholamines can affect semantic aspects of sentence comprehension. Whether these neuromodulatory systems also influence syntactic processing—how the brain combines words into grammatical structures—was largely unknown.”
When Grammar Forces a Rethink
Understanding a sentence involves more than knowing what its words mean. Readers also have to work out how those words fit together, sometimes revising an interpretation as new information arrives. The researchers used temporarily ambiguous “garden-path” sentences to examine that process.
Consider “The fan attacked the drummer, and the guitarist packed the instruments up.” When the words appear one at a time, readers may initially group “the drummer and the guitarist” together as the people being attacked. The word “packed” reveals that the guitarist is instead performing a separate action, requiring readers to rebuild their interpretation.
To test whether brain chemistry influences this revision, the team recruited 30 healthy adults. Each completed two sessions, once after taking methylphenidate, a stimulant commonly prescribed for ADHD that increases catecholamine levels, and once after taking a placebo.
Participants read ambiguous and unambiguous sentences and answered comprehension questions after each one. Meanwhile, researchers recorded their brain activity using EEG (electroencephalography), allowing them to examine the response at the precise word that exposed the grammatical ambiguity.
Brain Chemistry and Mental Effort
After methylphenidate, participants showed a stronger P600 response at the critical word, such as “packed.” This well-known EEG signal is associated with demanding grammatical processing and reflects increased cognitive effort. Its enhancement suggests that higher catecholamine levels changed how the brain recruited resources to resolve the sentence.
The increase was greatest among participants whose working memory capacity was lower before treatment.
“The findings suggest that catecholaminergic systems contribute to the dynamic allocation of cognitive resources during syntactic processing,” says Hagoort. “Their influence on language therefore appears to extend beyond semantic processing to syntactic unification, and the magnitude of this effect may depend on individual baseline working memory performance.”
“The results support the development of neuropharmacolinguistics as a field linking neuromodulatory systems to language processing.”
Reference: “Neuropharmacology of language: ERP evidence for catecholaminergic modulation of syntactic processing” by Yingying Tan, Ashley G. Lewis, Iris C. Schmits, Robert-Jan Verkes, Roshan Cools and Peter Hagoort, 22 October 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2606806123
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