Interbrain Synchrony When neural activities align between people during social interactions

Interbrain synchrony occurs when aspects of neural activity become aligned between people during social interaction. It has been observed during conversation, joint attention, cooperation and other shared activities. The research offers intriguing evidence that interacting brains are not operating entirely independently, although what this synchrony means and what causes it are still being explored.

Interbrain synchrony, sometimes called brain-to-brain coupling or interpersonal neural synchrony (INS), refers to measurable relationships between the neural activity of two or more people during social interaction.

This does not mean that two brains literally become synchronised in every respect, nor does it imply direct communication between brains. Rather, particular patterns of neural activity can become temporally aligned or correlated as people attend to, communicate with and respond to one another.

The phenomenon is especially interesting because neuroscience has traditionally studied one brain at a time. Increasingly, researchers are studying two or more brains simultaneously while people actually interact.

How interbrain synchrony is studied

One approach is known as hyperscanning. It allows researchers to record brain activity from two or more people at the same time while they engage in conversation, cooperation, joint attention or other forms of social interaction.

Techniques include electroencephalography (EEG), functional magnetic resonance imaging (fMRI), and functional near-infrared spectroscopy (fNIRS). These measure different aspects of brain activity and allow researchers to examine whether changes in one person’s neural activity are systematically related to changes in another’s.

Synchrony has been observed in a range of contexts, including conversation, joint attention, cooperative tasks, music-making and shared emotional experiences.

But synchrony needs to be interpreted carefully. Two people may show similar neural responses simply because they are seeing or hearing the same thing. They may also become more aligned because they are paying attention to each other, coordinating their actions or developing a shared understanding.

Synchrony may therefore be part of successful interaction, a consequence of it, or both. Establishing cause and effect is difficult.

Speaker-listener neural coupling

One particularly relevant study is the 2010 research by Greg J. Stephens, Lauren J. Silbert and Uri Hasson, Speaker-listener neural coupling underlies successful communication.

Rather than studying speaking and listening separately, the researchers examined the brain activity of a speaker telling a story and listeners hearing that story.

They found measurable coupling between aspects of the speaker’s and listeners’ brain activity. Importantly, stronger speaker-listener coupling was associated with better comprehension.

This does not mean that thoughts were somehow being transmitted directly from one brain to another. The coupling arose through ordinary human communication: speaking, listening, interpreting and anticipating meaning.

But it provides striking evidence that successful communication can involve measurable relationships between the neural processes of speaker and listener.

Speaker-listener Neural Coupling Underlies Successful Communication

Greg J. Stephens, Lauren J. Silbert, and Uri Hasson (2010)

Communication involves both speaking and listening. Traditional research has studied these processes separately within individual brains. This study examines brain activity in speakers and listeners during natural conversation, revealing coupled neural responses that correlate with effective communication. Continue reading

Two brains in conversation

Conversation provides a particularly interesting setting in which to think about interbrain synchrony.

When two people converse, each person’s behaviour continually changes what happens next for the other. A question redirects attention. A facial expression changes how a remark is interpreted. A pause may encourage someone to continue speaking. A puzzled look may cause an explanation to be reformulated.

Even conversational turn-taking requires remarkable coordination. We continually anticipate when another person is approaching the end of their turn and prepare our own response.

Conversation is therefore a continuous feedback process involving attention, perception, prediction, interpretation and response.

The two brains remain physically separate, but the cognitive processes taking place within them are not entirely independent. Each participant is continually responding to the other, and each response changes what becomes possible next.

Interbrain synchrony provides one measurable indication of this coordination.

Does more synchrony mean better conversation?

It is tempting to assume that greater synchrony must mean better communication, greater empathy or stronger social connection. The research does not justify such a simple conclusion.

Studies have found associations between interbrain synchrony and phenomena such as cooperation, shared attention, social connection, learning and successful communication. But an association does not necessarily tell us what is causing what.

Synchrony may arise because people understand each other better. Better understanding may arise partly because their cognitive processes are becoming coordinated. Or both may result from some other feature of the interaction.

Context also matters. Synchrony is not necessarily desirable in itself. Effective thinking together may sometimes depend upon disagreement, difference and cognitive tension rather than alignment.

The interesting finding is therefore not simply that “more synchrony is better”. It is that social interaction can produce measurable relationships between the activity of different brains.

Interbrain synchrony and interthinking

This has an intriguing connection with interthinking, the idea that we can use language to think collectively.

Interbrain synchrony is not the same thing as interthinking.

People may exhibit neural synchrony without engaging in the kind of joint exploration and development of ideas that interthinking describes. And finding synchrony between two brains does not demonstrate that a thought somehow exists independently between them.

The neuroscience therefore does not prove interthinking.

What it does provide is another reason to question the simple picture of conversation as two independent minds exchanging already completed thoughts.

During interaction, attention, perception, prediction, language and behaviour can become dynamically coupled. What one person says changes what another attends to and thinks about. Their response then changes what becomes possible for the first person to think next.

When a conversation involves questioning, exploring, challenging and building upon each other’s thoughts, this becomes particularly interesting. New understandings can emerge through a process in which neither participant’s thinking is entirely independent of the other.

Interbrain synchrony is therefore consistent with a broader view of cognition as socially interactive rather than simply the activity of isolated brains exchanging information.

Does synchrony imply a shared mind?

Interbrain synchrony raises a fascinating question. If aspects of the activity of two brains can become coordinated, does this suggest that consciousness itself can somehow extend between people?

Some researchers and theorists have explored ideas of extended consciousness. Such ideas remain highly speculative.

Neural synchrony does not demonstrate shared consciousness. Coordinated neural activity and shared conscious experience are very different claims, and our scientific understanding of consciousness itself remains incomplete.

It is also important to distinguish extended consciousness from the Extended Mind Hypothesis associated with philosophers Andy Clark and David Chalmers.

The Extended Mind Hypothesis is principally a claim about cognition. It proposes that under some circumstances cognitive processes can extend beyond the brain and make use of things in the external world. This is not the same as claiming that consciousness itself extends between people.

Another related concept is Collective Consciousness, which concerns the shared beliefs, ideas and attitudes of groups and societies. This has a long history in sociology but should not be confused with the neuroscientific phenomenon of interbrain synchrony.

These distinctions matter. Interesting scientific findings can easily acquire interpretations that go far beyond what the evidence supports.

Research challenges

Research into interbrain synchrony is still developing, and interpreting the findings is difficult.

Brain signals are complex, and apparent synchrony can have many causes. Participants may be responding to the same stimulus, coordinating their behaviour, sharing attention or genuinely responding to one another. Researchers need to distinguish between these possibilities.

Individual differences also matter. Neural activity varies substantially between people, tasks and contexts, making broad generalisations difficult.

There are ethical questions too. As technologies for recording and interpreting neural data develop, questions of privacy, consent and the appropriate use of such information will become increasingly important.

Interbrain synchrony does not mean that two brains become one, nor does it prove that people literally share thoughts. It reveals something subtler and perhaps more interesting: during social interaction, the activity of separate brains can become measurably related. Conversation is not simply an exchange between isolated minds. It is a dynamic process in which each person’s attention, behaviour and thinking continually shape what happens next in the other.

Resources

• Article: Interbrain Synchrony: Can consciousness extend across multiple brains?
• Paper: How emotional disclosure enhances interpersonal closeness from a speaker-listener perspective: An fNIRS hyperscanning study