Pronouns like “he” and “she” enhance our understanding of language, but their meanings vary based on context. An international team of neuroscientists, neurosurgeons, and neurologists conducted research to explore how our brains connect pronouns to their referents.
Doris Dijksterhuis and Matthew Self, working with Pieter Roelfsema’s group, examined brain activity in epilepsy patients who had depth electrodes implanted in their hippocampus, a region crucial for learning and memory.
It is possible to measure the activity of individual brain cells in the hippocampus while the patient performs a task. In the hippocampus, specialized “concept cells” activate in response to specific individuals, such as the famous “Jennifer Aniston cell,” which responds to her name or image.
Scientists aimed to determine whether these cells activate when encountering pronouns like “he” or “she.” They explored whether these cells can connect the pronoun to the correct person, investigating the underlying mechanisms of how pronouns are linked to their referents.
Doris Dijksterhuis: “To test this, we first showed the patients many photos until we found a cell that responded to one particular image. For example, we found a cell that responded to an image of ‘Shrek’ but not other images. We call this cell a ‘Shrek concept cell.’”
“When patients later read a sentence like: “Shrek and Fiona were having dinner. He poured out some wine.” the ‘Shrek’ cell responded to the word “Shrek” and the pronoun ‘He.’ This is interesting because such a pronoun can mean something entirely different in another sentence.”
“For example, in the sentence ‘Donald Trump and Kamala Harris were having dinner. He poured out some wine,’ the same pronoun, ‘He,’ refers to Donald Trump, and therefore the Shrek cell will not react. Individual hippocampal cells track who the pronoun refers to in a dynamic, flexible way.”
Matthew Self from Pieter Roelfsema said, “We had the participants answer a question at the end of the sentences about who acted. Based on the activity of the individual concept cells, we could predict whether the patients would give the correct answer.”
“To make it a bit more challenging, we also added some trick questions, with two people of the same gender: “Jennifer Aniston and Kamala Harris walked into a bar. She sat at the table.”
“The patient had to decide themselves who acted. We observed that patients tended to choose the person that evoked the most activity in the hippocampus at the start of the sentence. This could be based on chance fluctuations in activity on a trial-by-trial basis or an internal preference for one of the two characters in the sentence.”
Dijksterhuis: “The hippocampus is important for learning and memory, but it remains unclear how it is involved in the interaction between memory and language. How do we remember what we’ve read? When you think of something you’ve read, you have different concepts that together create the story.”
“Pronouns help us to understand who did what in the story, and cells in the hippocampus encode these actions into our memory. Ultimately, we want to know how an entire memory is formed and represented in the brain.”
“It is of great value that this group of patients has given their permission to participate in our research. We can only very rarely measure the activity of single brain cells in reading people, and it is impossible to study these processes in animals. When we get the chance, we try to get as much out of it as possible.”
Journal Reference:
- D. E. Dijksterhuis, M.W. Self, J. K. Possel et al. Pronouns reactivate conceptual representations in human hippocampal neurons. Science. DOI: 10.1126/science.adr2813