A recent study reveals how individual brain cells in the hippocampus react to pronouns, which could shed light on how we remember what we read.
Consider the sentence: “Donald Trump and Kamala Harris walked into the bar, she sat down at a table.” Instantly, we know that it was Kamala who took a seat, not Donald. Pronouns such as “she” assist us in comprehending language, but they can have varying interpretations. Our understanding of which noun a pronoun refers to depends on the context. So, how do we become adept at this, and what mechanisms in our brain connect pronouns to their corresponding nouns?
To explore this, a global team of neuroscientists, neurosurgeons, and neurologists collaborated. Doris Dijksterhuis and Matthew Self, part of Pieter Roelfsema’s team, examined brain activity in epilepsy patients. These individuals had depth electrodes implanted in their hippocampus, a region crucial for learning and memory, to aid in their treatment. The research team took this opportunity to conduct further assessments.
“We can observe the action of individual brain cells in the hippocampus while the patient engages in a task,” explains Matthew Self. Within the hippocampus, there are cells that respond to specific individuals, known as “concept cells.” A famous example is the “Jennifer Aniston cell,” which activates upon seeing her photo, hearing her name, or reading her name. We were curious to see if these cells would also activate when a pronoun like ‘he’ or ‘she’ is read. Can these cells associate the pronoun with the correct individual?
Shrek cell
Doris Dijksterhuis states: “To test this, we initially showed the patients numerous photos until we identified a cell that reacted to a specific image. For instance, we found a cell that responded to an image of ‘Shrek’ but not to others. We named this the ‘Shrek concept cell.’ Later, when patients read a sentence like: “Shrek and Fiona were dining together. He poured some wine,” the ‘Shrek’ cell responded to the word “Shrek,” as well as the pronoun ‘He.’ This is fascinating since such a pronoun could imply a different subject in another sentence. For example, in the sentence ‘Donald Trump and Kamala Harris were having dinner. He poured some wine,’ the pronoun ‘He’ refers to Donald Trump, thus the Shrek cell would not activate. Each hippocampal cell identifies the pronoun’s referent in a dynamic and adaptable manner.”
Self adds: “We had the participants respond to queries at the conclusion of the sentences regarding who performed the action. We could anticipate whether the patients would provide the correct response based on the activity of the individual concept cells. To heighten the challenge, we added trick questions involving two individuals of the same gender: “Jennifer Aniston and Kamala Harris walked into a bar. She sat at the table.” The patient had to determine who took the action. We noted that patients generally opted for the person that activated the most activity in the hippocampus at the sentence’s onset. This could stem from random variations in activity from trial to trial or an inherent preference for one of the two characters in the sentence.”
The bigger picture
Dijksterhuis remarks: “While the hippocampus is vital for learning and memory, the nature of its involvement in the relationship between memory and language remains unclear. How do we retain what we’ve read? When recalling something, various concepts come together to form the narrative. Pronouns assist us in understanding the actions within the story, and the cells in the hippocampus encode these actions in our memories. Ultimately, we aim to comprehend how a complete memory is constructed and represented in the brain.”
“It’s incredibly valuable that this group of patients has consented to participate in our research. The opportunity to measure the activity of single brain cells in reading individuals is rare, and studying these processes in animals is impossible. When we get the chance, we strive to extract as much information as possible.”
Source: Science
