Imagine that a device was invented which could record all of my memories, dreams and ideas, and then transmit the entire contents to your brain. Sounds like a game-changing invention, right? In fact, we already possess such a technology — it’s called effective storytelling. Human lives revolve around this ability to share information and experiences, and as a scientist, I’m fascinated by how our brains produce and comprehend interpersonal communication. Since 2008, my lab in Princeton has been focused on the question: How exactly do the neuron patterns in one person’s brain that are associated with their particular stories, memories and ideas get transmitted to another person’s?
Through our work, we believe we’ve uncovered two of the hidden neural mechanisms that occur during an exchange: 1) a person’s brain becomes physically coupled to the sound wave that the other person is transmitting via language to their brain; 2) our brains have developed a common neural protocol that allows us to communicate. Let me take you through the research that brought us here.
In one experiment, we brought people to the fMRI scanner and scanned their brains while they were either telling or listening to recordings of real-life stories. When we looked at the auditory cortex — the part of the brain that processes the sounds coming from the ear — of a listener, we saw that her neural responses went up and down as the storyteller shared his tale.
Which made us wonder: how similar would the responses be across multiple listeners? We scanned the brains of five listeners while they were at rest and waiting for the storyteller to begin, and saw that although their auditory cortices were all active, their responses were very different and not in sync with one another (see the inset bubble at right).
However, immediately as the story started, we saw something amazing happen. Suddenly, we saw the responses in all of the subjects begin to lock together and go up and down in a similar way.
Scientists call this effect “neural entrainment.” But what factor was driving this neural entrainment: the sounds that the speaker was producing; the words the speaker was saying; or meaning that the speaker was trying to convey?
So, we experimented. First, we took the story and played it backwards. This preserved many of the original auditory features but completely removed the meaning. We found that the backwards sounds induced entrainment, or alignment, in the auditory cortices in all of the listeners’ brains but did not spread any deeper into their brains.
Next, we scrambled the words in the story, so while each word was comprehensible, all together it sounded like a list of unconnected words. We saw the words begin to induce alignment in the early language areas of our subjects’ brains, but not beyond that.
Then, we took the words and built sentences from them. But while the sentences individually made sense, they did not work together to tell a story. As an example, here’s one fragment the listeners heard: “And they recommend against crossing that line. He says: ‘Dear Jim, Good story. Nice details. Didn’t she only know about him through me?’”
When we played this version, we saw activity in the areas which process incoming language become aligned across all listeners in parts of their brains. But only after we played the full, engaging, coherent story for listeners did the responses spread deeper into their brains into their higher-order areas — including the frontal cortex and the parietal cortex — and made all of these areas respond very similarly (below).
As a result of these experiments, we concluded the responses became similar across listeners due to the meaning conveyed by the speaker, not because of the sounds or individual words. If that was true, we predicted that if we told two different listeners the exact same story using two very different sets of words, their brain responses would still be similar. To find out, we did the following experiment. We took our story, which had been told in English, and translated it into Russian.
When we played the English story to English listeners and the Russian story to Russian listeners, we compared their neural responses. We did not see similar responses in their auditory cortices, which was expected because the sounds in each language are very different. However, we observed the responses in the higher-order areas to be similar across the two groups of listeners. We deduced this was because they had a similar understanding of the story, and we confirmed that they did by testing them after the story ended.
Okay, so now we had an idea of the process happening in a listener’s brain. But what was going on in the speaker’s brain? We asked the storyteller to go into the fMRI scanner and compared his brain responses to the brain responses of the listeners listening to the story. Remember, producing speech and comprehending speech are two very different processes. But to our surprise, we saw all the complex patterns within the listeners’ brains actually came from the speaker’s brain (below).
What’s more, we found the better and more effective the communication, the stronger the similarity between the listener’s brain and the speaker’s brain. In other words, when speaker and listener really understood each other, their brain responses were very similar.
Which led my researchers and I to ask: How do we transmit a memory from one person’s brain to another? So we did the following experiment. We had people watch — making sure it was for the first time in their lives — a particular episode from the BBC TV series Sherlock while we scanned their brains. Later, we asked them to return to the scanner and relate this episode as a story to a person who had never seen it.
In the episode, Sherlock entered a cab that turned out to be driven by the murderer he had been looking for. As our lab subjects watched this scene, we observed a specific pattern in their brains. But we were really surprised to see that even when this scene was described in words from a viewer to a non-viewer, both people showed a very similar pattern in their brains. So we’re able to achieve neural entrainment even when we are sharing only our memories — not even the real experience — with another person.
Yet even hearing — or being told — the same story is not always enough. Sometimes, people can understand the exact same story in different ways. To test this in the lab, we conducted another experiment. We used the J.D. Salinger story “Pretty Mouth and Green My Eyes,” in which a husband loses track of his wife in the middle of a party. The man ends up calling his best friend, asking, “Did you see my wife?” We told half of the subjects in our study that the wife was having an affair with the best friend; with the other half, we said the wife was loyal and the husband was very jealous.
Interestingly, this one sentence we told subjects before the story started was enough to make the brain responses of all the people who believed the wife was having an affair to be very similar in high-order areas and to be different from the group who thought her husband was unjustifiably jealous.
This finding has implications beyond our lab experiment. If one sentence was enough to make a person’s brain similar to people who had the same belief and different from people who held different beliefs, imagine how this effect might be amplified in real life. As our experiments show, good communication depends on speakers and listeners possessing common ground. Today, too many of us live in echo chambers where we’re exposed to the same perspective day after day. We should all be concerned as a society if we lose a common ground and lose the ability to communicate effectively with people who are different than us.
As a scientist, I’m not sure how to fix this. One way to start might be to go back to having dialogues with each other, where we take turns speaking and listening. Together we hash out ideas and try to come to a mutual understanding. Such conversations, as our experiments show, result in coupling in our brains, and the people we’re coupled to define who we are — think how you much you change on a daily basis from your interactions and your coupling with the people you encounter. I think the most important thing is just to keep being coupled to other people, to keep communicating with them and to keep spreading ideas. Because the sum of all of us together, coupled, is far greater than the sum of our parts.
Illustrations courtesy of Uri Hasson