Where Does a Brain End When We Begin to Act as “We”?

When Words Begin to Trap Us

BrainLatam Special Series — SBNeC 2026

Let us begin without EEG.

Imagine a horse and a rider in motion.

The rider adjusts their body.

The horse perceives it.

Responds.

That response changes the rider again.

And the cycle continues:

horse perceives
→ responds
→ rider perceives
→ responds.

The horse remains a horse.

The rider remains a rider.

But the movement we see does not completely belong to either one.

It emerges from the relationship between them.

At BrainLatam, we have already used this horse-rider system to ask what happens when two Body-Territories stop merely coexisting and begin to reciprocally modify each other’s movements.

Now we can bring the question back to us:

When you and I need to coordinate our actions, does something emerge that can only exist because there is a “we”?

Coordination does not mean disappearing into the other

This distinction matters.

High performance between horse and rider does not require one to disappear into the other.

Nor does it require one to completely control the other.

There is difference.

There is initiative.

There is response.

There is adjustment.

Something similar happens in music.

Two musicians do not need to play the same note.

In a conversation, we do not need to think alike.

In a team, we do not need to make exactly the same movement.

Perhaps the most interesting coordination happens precisely when:

we remain different and still manage to produce together something that did not exist for either of us in isolation.

This idea prepares the ground for an Aymara word:

Jiwasa.

But before getting there, we need to enter the laboratory.

What if we could experimentally modify the “between us”?

In 2025, Ivo Leiva-Cisterna, Paulo Barraza, Eugenio Rodríguez, and Guillaume Dumas carried out a particularly important experiment in Chile.

A large part of hyperscanning research simultaneously records the brain activity of two people and looks for synchronization during interaction.

But there is a problem.

Synchronization does not necessarily mean cooperation.

The two brains may simply be responding to the same stimulus.

Leiva-Cisterna and colleagues tried to go beyond correlation.

They formed 30 dyads and used simultaneous rhythmic visual stimulation at 16 Hz and 40 Hz, while the participants performed a task that depended on coordination between them.

The stimulation increased inter-brain synchronization at the target frequencies and, especially in the 16 Hz condition, favored more sustained behavioral coordination.

This changes the question.

We are no longer simply saying:

“two people cooperated and their brains synchronized.”

The experiment managed to intervene in the coupling and observe a change in cooperative behavior.

The authors present the result as causal evidence for a functional contribution of inter-brain synchrony to dyadic coordination.

They did not create a collective brain.

They did not merge two consciousnesses.

But they showed something fascinating:

modifying a property of the relationship between two systems can modify what they are able to do together.

Perhaps the relevant unit is not always only “me”

Neuroscience needs to isolate variables.

We place one person in front of a task.

We measure their EEG.

Their behavior.

Their response.

This isolation has produced enormous knowledge.

But it has a limit.

If what we want to explain only happens when another person is present, studying a single brain may leave an important part out.

Researchers in Mexico have been addressing exactly this problem.

Pablo Nogueira-Islas, Paola Olguín-Rodríguez, and colleagues proposed an EEG hyperscanning paradigm to compare cooperation and competition, including control conditions designed to better distinguish synchrony arising from interaction from synchrony produced simply by shared external stimuli.

This reminds us of an important rule:

Synchronizing does not, by itself, mean forming a “we”.

Jiwasa changes the question

Now we can return to the Andes.

In the Aymara language there is Jiwasa, used for an inclusive “we” involving both the speaker and the person being addressed.

Peruvian researchers such as Saúl Bermejo-Paredes and Yanet Maquera-Maquera discuss this relational structure of the Aymara language in research published in 2025.

We do not want to turn Jiwasa into a translation of:

cooperation

or:

brain synchronization.

Much less do we want to say that an ancestral word was describing hyperscanning.

We want to allow the word to open a window.

We usually ask:

What happens to me when I cooperate with you?

Jiwasa lets us try another question:

What happens to us when the outcome depends on our relationship?

It seems like a small change.

But it may change the variable we are interested in.

From “I can” to “we can”

Let us return to the horse and rider.

The rider does not produce the movement of the whole system alone.

Neither does the horse.

Now think of two people carrying a table.

One lifts first.

The other senses it.

Adjusts.

The first responds again.

Within seconds, a sequence of anticipations and corrections appears.

We could ask:

Who is controlling whom?

Perhaps that is the wrong question.

We could ask instead:

How are we managing to coordinate?

That difference matters.

Because Jiwasa does not need to mean that the “I” disappears.

It may mean that a new scale of observation has appeared:

I
↔ you
→ we.

Synchrony, coordination, and Jiwasa are not the same thing

We need to separate three ideas.

SYNCHRONY

Some variables begin to change together.

COORDINATION

My behavior begins to depend on yours, and yours on mine.

JIWASA

BrainLatam asks whether we can investigate situations in which what we are doing begins to be represented and constructed as something that actually includes both of us.

This distinction protects us.

A crowd may march in synchrony under coercion.

Millions of people may watch the same video.

Two brains may respond similarly to the same stimulus.

That does not automatically mean:

reciprocity;

cooperation;

shared agency.

Even a Jenga game can reveal the difference

In 2026, researchers in Chile recorded pairs of Latin American friends with mobile EEG while they performed a Jenga task together.

They found increased synchronization in some frequencies during cooperation, but controls with “artificial dyads” showed that part of the effect could be related to the shared task itself rather than to the specific relationship between those partners.

Other components showed greater specificity to the pair.

This result is very important for our proposal.

It prevents us from romanticizing synchronization.

Doing the same thing does not necessarily mean doing something together.

And during a conversation?

In 2026, Marcos Domínguez-Arriola and colleagues simultaneously recorded EEG during free conversations between people who did not know each other.

Higher perceived interaction quality was associated with certain patterns of inter-brain coordination, while more positive mutual impressions were also related to convergence in features of speech.

Perhaps all of us have felt something like this.

There are conversations in which we simply exchange sentences.

And there are others in which, after a few minutes, something begins to happen between us.

An idea appears.

Neither person brought it ready-made.

It emerged while we were talking.

The “we” does not need to end with humans

Here Ailton Krenak can widen our window.

In Ancestral Future (Futuro ancestral, 2022), Krenak questions the radical separation between humanity, rivers, territory, and what we usually call nature.

In his reflection, the future cannot be separated from the relationships that sustain life.

This allows BrainLatam to expand the spiral:

I
→ you
→ Jiwasa
→ community
→ territory
→ Biome.

Not as a neuroscientific conclusion.

As a question.

If horse and rider help us perceive coordination across species, perhaps we should also ask:

How far should the “we” extend when our decisions depend on water, forests, animals, climate, and territory?

Science, Politics, and Religion when the “we” appears

Now we can bring back our three operations.

Religion → Expecting / Transcending

Alone, I may ask:

What future do I want for myself?

In Jiwasa:

What future can we imagine for us?

Politics → Judging / Choosing

Alone:

Which alternative benefits me more?

In Jiwasa:

Which decision improves our condition without erasing any of the Body-Territories involved?

Science → Doing

Alone:

What can I do?

In Jiwasa:

What can we do only because we coordinate our differences?

The word “we” has changed all three questions.

From two brains to a Constitution?

Now we can move up another scale.

Two Body-Territories need to coordinate a task.

If they remain together, expectations may appear.

Then patterns.

Then rules:

when you do this, I do that.

In larger groups, we need to coordinate:

who does what;

when;

how;

who decides;

how conflicts are corrected.

And at larger scales still, institutions appear.

We cannot say:

brain synchronization → Constitution.

That leap would be false.

But we can investigate each transition:

Body-Territories
→ coordination
→ cooperation
→ shared expectations
→ rules
→ institutions.

At each step we ask:

what emerged here that did not exist at the previous scale?

A Constitution may seem very far from two brains cooperating.

But there is a question shared by both extremes:

What rules allow different Body-Territories to continue coordinating their lives without one having to disappear inside the other?

Where does a brain end?

Perhaps the title has misled us.

Anatomically, the brain ends inside the organism.

But perhaps that is not the most interesting question.

We can reformulate it:

Where does an explanation based on only one brain stop being enough?

When an action only exists because you respond to me while I respond to you, perhaps looking at only one of us is no longer sufficient.

The “we” does not need to become a mystical entity.

It does not need to have a brain.

It may be something simpler:

a relationship that opens possibilities of action that none of its participants possessed alone.

The horse remains a horse.

The rider remains a rider.

You remain you.

I remain me.

And perhaps Jiwasa begins exactly there:

when our differences continue to exist, but something appears that we can only do because we are together.

BrainLatam Question

If there are possibilities that only appear when we coordinate our differences, can we build a Science, a Politics, and a way of imagining the future that know how to ask not only “what can I do?”, but also “what can we do together without any of us having to disappear?”

Latin American References and Conceptual Windows

Leiva-Cisterna, I.; Barraza, P.; Rodríguez, E.; Dumas, G. (2025). Sensory multi-brain stimulation enhances dyadic cooperative behavior. Social Cognitive and Affective Neuroscience, 20(1), nsaf104. Work carried out primarily in Chilean research centers using multi-brain sensory stimulation, EEG, and a cooperative task to causally investigate inter-brain synchronization and coordination.

Nogueira-Islas, P. A.; Olguín-Rodríguez, P. V.; Tlahuext-Aca, H.; Müller, M. F. (2025). Uniform hyperscanning paradigm to study cooperation and competition. MethodsX, 14, 103139. Researchers linked to UNAM and Mexican institutions propose controls to distinguish genuine interaction from synchronization caused by common stimuli.

Bermejo-Paredes, S.; Maquera-Maquera, Y. A. (2025). Lenguaje, comprensión del ser y transformación del sistema sexo-género en indígenas aimara del sur peruano. Peruvian research discussing relational structures of the Aymara language and Jiwasa as an inclusive form of “we”.

Valenzuela, L.; Pérez-Arenas, X.; Medel, V.; Soto, V. et al. (2026). Aperiodic activity shapes inter-brain synchrony during cooperative puzzle solving. NeuroImage, 338, 122116. Mobile EEG in pairs of Latin American friends during cooperation, distinguishing task-related effects from those specific to the relationship between partners.

Domínguez-Arriola, M. E.; Lam, P. C. H.; Pérez, A.; Pell, M. D. (2026). Interpersonal neural coordination tracks interaction quality during naturalistic conversation. NeuroImage, 338, 122090. EEG hyperscanning during natural conversations and the relationship between neural coordination, interaction quality, and speech convergence.

Krenak, A. (2022). Futuro ancestral. Companhia das Letras. An Indigenous Brazilian intellectual window for expanding the “we” toward territory, rivers, and the conditions that sustain the continuity of life.

BrainLatam (2026). Onde termina uma mente durante uma conversa? Develops the horse-rider system as a way to think about reciprocal perception, coordination, difference, Jiwasa, and shared agency.