How the Brain Distinguishes Fact From Possibility

Summary: The human brain contains a perspective-adjusted neural representation for factual information and more elusive cortical signaling representing the computations of possibilities.

Source: SfN

Processing certain factual information elicits stronger brain activity than uncertain information, according to research recently published in eNeuro.

Modal language like “might” and “may” allows humans to speculate about possibilities, in both the real world and fictional ones. When reading a story, the brain adds new information to a model of the developing situation. But not all information is certain — think “Sarah owns a cat” vs. “Sarah might own a cat.” So, how does the brain differentiate the two?

Tulling et al. used magnetoencephalography to compare how the brain processes factual and modal language in short narratives. Factual sentences contained the verb “do,” and modal sentences contained the verbs “may,” “might,” or “must.”

Factual sentences elicited stronger brain activity than modal sentences within 200 milliseconds of the target verb appearing. This suggests the brain was adding the factual but not uncertain information to its model of the described situation. But the location of the increased activity differed, potentially due to perspective.

This shows brain scans from the study
A full-brain analysis revealed a significant effect for modal force, eliciting stronger activity for the factual condition over the modal conditions. Credit: Tulling et al., eNeuro 2020

Updating the representation of a story character’s beliefs increased activity in right temporoparietal areas, while updating one’s own increased activity in frontal medial areas.

These findings suggest the human brain contains a robust, perspective-adjusted neural representation of factual information and more elusive cortical signals reflecting the computation of possibilities.

About this neuroscience research news

Source: SfN
Contact: Calli McMurray – SfN
Image: The image is credited to Tulling et al., eNeuro 2020

Original Research: Closed access.
Neural Correlates of Modal Displacement and Discourse-Updating Under (Un)Certainty” by Maxime Tulling, Ryan Law, Ailís Cournane and Liina Pylkkänen. eNeuro


Neural Correlates of Modal Displacement and Discourse-Updating Under (Un)Certainty

A hallmark of human thought is the ability to think about not just the actual world, but also about alternative ways the world could be. One way to study this contrast is through language. Language has grammatical devices for expressing possibilities and necessities, such as the words might or must. With these devices, called “modal expressions,” we can study the actual versus possible contrast in a highly controlled way. While factual utterances such as “There is a monster under my bed” update the here-and-now of a discourse model, a modal version of this sentence, “There might be a monster under my bed,” displaces from the here-and-now and merely postulates a possibility. We used magnetoencephalography (MEG) to test whether the processes of discourse updating and modal displacement dissociate in the brain. Factual and modal utterances were embedded in short narratives, and across two experiments, factual expressions increased the measured activity over modal expressions. However, the localization of the increase appeared to depend on perspective: signal localizing in right temporo-parietal areas increased when updating the representation of someone else’s beliefs, while frontal medial areas seem sensitive to updating one’s own beliefs. The presence of modal displacement did not elevate MEG signal strength in any of our analyses. In sum, this study identifies potential neural signatures of the process by which facts get added to our mental representation of the world.

Significance Statement 

When we say things like “There might be a monster under my bed” we distance ourselves from the observable here-and-now and imagine how the world could be. Normally, we are easily able to distinguish reality from mere possibility, but we know very little about the neural mechanisms that allow us to do so. Our research shows that the brain responds differently to utterances about the here-and-now compared with utterances conveying possibilities. This means that our brains separate factual information from hypothetical information, raising interesting new questions about the representation of possibilities in discourse comprehension. By identifying the neural correlates of updating discourse representations, we pave the way for future research on the processing and representation of non-factual discourse.

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