How pronouns are processed in the memory region of the human brain

A new study shows how individual brain cells in the hippocampus respond to pronouns. “It can help us understand how we remember what we read,” the authors say. Their research is published in the journal Science.

Read the following sentence: “Donald Trump and Kamala Harris walked into the bar, she sat down at a table.” We all know immediately that it was Kamala who sat at the table, not Donald. Pronouns like “she” help us understand language, but pronouns can have multiple meanings. Depending on the context, we understand who the pronoun refers to. But how come we’re so good at it, and how do our brains connect pronouns to their nouns?

To answer this question, an international team of neuroscientists, neurosurgeons and neurologists joined forces. Doris Dijksterhuis and Matthew Self from Pieter Roelfsema’s group studied with their colleagues the brain activity of epileptic patients.

As part of their treatment, these patients had electrodes implanted deep into their hippocampus, a brain area involved in learning and memory. The research team took advantage of this and carried out additional tests with them.

“We can measure the activity of individual brain cells in the hippocampus while the patient performs a task,” explains Matthew Self.

“In the hippocampus, there are cells that respond to a specific person, called “concept cells.” A well-known example is the “Jennifer Aniston cell,” which becomes active when you see a photo of Jennifer Aniston, hear her name, or read the words “Jennifer Aniston.” We wondered if these cells also became active when you read only a pronoun, like “he” or “she.” Are these cells capable of linking the pronoun to the right person? »

Shrek Cell

Doris Dijksterhuis explains: “To test this, we first showed patients many photos until we found a cell that responded to a particular image. For example, we found a cell that responded to an image of “Shrek” but not to other images. We call this cell a “Shrek concept cell.” When patients later read a sentence such as: “Shrek and Fiona were having dinner, he poured wine”, the “Shrek” cell indeed responded to the word “Shrek”, but also to the pronoun “He”.

“It’s interesting because such a pronoun can mean something completely different in another sentence. For example, in the sentence ‘Donald Trump and Kamala Harris were having dinner. He poured wine”, the same pronoun “He” refers to Donald Trump, and therefore the Shrek cell, will not react. Individual cells in the hippocampus dynamically and flexibly track who the pronoun refers to.

Self adds: “We asked participants to answer a question at the end of the sentences about who performed the action. We could predict whether patients would give the correct response based on the activity of individual concept cells.

“To make things a little more difficult, we also added a few trick questions, with two people of the same sex: ‘Jennifer Aniston and Kamala Harris walked into a bar. She sat at the table.’ The patient had to decide for himself who performed the action. We observed that patients tended to choose the person who evoked the most activity in the hippocampus at the beginning of the sentence. This could be based on random fluctuations. of activity during a trial by trial or an internal preference for one of the two characters of the sentence.

The big picture

Dijksterhuis says: “The hippocampus is important for learning and memory, but it is still unclear how the hippocampus is involved in the interaction between memory and language. How do we remember what we have read? When you think about something you’ve read, you have different concepts that together create the story.

“Pronouns help us understand who did what in the story, and cells in the hippocampus encode these actions in our memory. Ultimately, we want to know how an entire memory is formed and represented in the brain.”

“It is very valuable that this group of patients has given their permission to participate in our research. We can only very rarely measure the activity of individual brain cells in people who read and it is impossible to study these processes in animals, when we have the opportunity, we try to make the most of it.”

Provided by the Netherlands Institute for Neuroscience – KNAW