Memory, brain, speech. How do we understand pronouns?
When it comes to communication and memory, science in general explains the nature of the abstract images that we exchange with each other. When the image of a “pen” or “laptop” pops into your head, it is thanks to individual connections of neurons, neural connections. But how does our brain react when it comes to pronouns? How do we understand their meaning?
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Pronouns and their meanings
Read the following sentence: “Harry Potter and Tanya Grotter entered the bar, and she sat down at the table.” We all immediately understand that Tanya sat down at the table, not Harry. Pronouns such as “he” and “she” help us understand a situation, but pronouns can change meaning depending on the context. At the same time, we understand perfectly well who we are talking about. But how is it that we are so good at it, and how does our brain associate pronouns with their nouns? Can we assume that other forms of consciousness use the same patterns?
To answer this question, an international team of neuroscientists, neurosurgeons and neurologists joined forces. Doris Dijksterhuis and Matthew Self from Peter Roelfsem's group and their colleagues observed the brain activity of patients with epilepsy. As part of the treatment, these patients had depth electrodes implanted in the hippocampus, an area of the brain responsible for learning and memory. The research team took advantage of this and ran additional tests on the electrodes.
We can measure the activity of individual brain cells in the hippocampus while the patient performs a task. The hippocampus contains cells that respond to a specific person, called “conceptual cells.” A famous example is the “Jennifer Aniston cell,” which is activated when you see a photo of Jennifer Aniston, hear her name, or read the words “Jennifer Aniston.” We wondered whether these cells also fire when you read only a pronoun, such as “he” or “she.” Are these cells able to associate the pronoun with the right person?
Matthew Self, co-author of the study.
Shrek's cage
To test the theory, the scientists first showed patients a series of photographs until they found a cell that responded to one specific image. For example, scientists found a cell that responded to the image of Shrek, but not to other images. The cell was called the “Shrek cell concept”. When patients later read a sentence like: “Shrek and Fiona were having lunch. He poured out some wine,” then the “Shrek” cell actually responded to the word “Shrek” and also to the pronoun “He.”
This is interesting because such a pronoun could mean something completely different in another sentence. For example, in the sentence “Harry Potter and Tanya Grotter had lunch. He poured out some wine” the same pronoun “he” refers to Harry Potter and therefore Shrek's cell will not react. Individual cells in the hippocampus keep track of which object a pronoun refers to. And they do it dynamically and flexibly. Especially when dopamine and norepinephrine in excess.
Progress of the study
The scientists asked participants to specify who exactly performed the action in a specific example. By observing the brain, scientists could predict in advance whether patients would give the correct answer. By the way, the same artificial intelligence is capable of not only predicting a person’s thoughts, but also making its own assumptions about the unfolding situation. And all thanks to the activity of individual conceptual cells.
To make it a little more challenging, the scientists also added some trick questions with two people of the same sex: “Jennifer Aniston and Kamala Harris walked into a bar. She sat down at the table.” The patient had to decide for himself who performed the action.
The scientists observed that patients tended to choose the person who generated the most activity in the hippocampus at the beginning of a sentence. This could be based on random fluctuations in activity varying from trial to trial, or on an internal preference for one of the two characters in the sentence.
The role of the hippocampus and the presence of meanings
The hippocampus is important for learning and memory, but exactly how it is involved in the interaction between memory and language remains unclear. How do we remember what we read? When you think about something you read, different concepts form in your mind and together they create a story.
Pronouns help us understand who did what in a story, and cells in the hippocampus encode those actions in our memory. Ultimately, we form, store and, if necessary, display an entire memory in the brain.
It is very valuable that this group of patients gave their permission to participate in our study. We can only very rarely measure the activity of individual brain cells in people who read text, and it is impossible to study these processes in animals. When we have such an opportunity, we try to extract as much potential from it as possible.
Words from the Study Authors
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