Body - Two Brains Are Not Enough - Brain, Heart, and Relationship

When we study two people interacting, we almost always begin by drawing two units:

Brain A ⇄ Brain B.

This image helped establish hyperscanning: recording two brains simultaneously and investigating how their dynamics converge, diverge, or reorganize during interaction.

But in 2026, Hong, Moore, and Quiñones-Camacho proposed that perhaps we need to observe more than one system at the same time.

Their question is both practical and scientific: how can we study caregiver–child co-regulation while temporally synchronizing brain activity, cardiac physiology, and behavior?

Instead of treating neural and physiological synchrony as separate phenomena, the authors developed a multimodal protocol integrating fNIRS, ECG, behavioral video, and experimental stimuli along a common temporal axis. This makes it possible to relate specific moments of interaction more precisely to neural and autonomic changes observed in both participants.

It is an important methodological advance.

But perhaps it also opens a larger question:

if what we are studying is a relationship, where is the relationship in our data?

What are Hong, Moore, and Quiñones-Camacho actually proposing?

The article is not simply the presentation of another piece of equipment.

It is a practical guide for making a technically difficult experimental design feasible: recording two participants simultaneously — including young children — across several modalities without losing temporal correspondence between the signals.

The authors use NIRSport2/NIRx for fNIRS, MindWare BioLab for ECG, Mangold VideoSyncPro for behavioral video, and PsychoPy for tasks and event markers. PsychoPy sends triggers to the different acquisition systems, allowing task onset, stimuli, responses, behavioral events, ECG, and fNIRS to be aligned. Video can then be related to physiological events within the same temporal window.

This detail is fundamental.

It is not enough to know that two people showed some degree of physiological correlation during twenty minutes of interaction.

It is much more informative to know what was happening when that correlation emerged.

The ongoing longitudinal study supporting the protocol follows children 3 to 7 years old, across two laboratory visits approximately one year apart. After individual tasks and a break, caregiver and child complete six short dyadic tasks, totaling roughly 35 minutes. These tasks were selected to generate different forms of interaction: jointly navigating uncertainty, solving problems, and engaging in less structured play. To maintain children's engagement, the activities are framed as stages in a “treasure hunt.”

The authors also report feasibility data from 85 participants: 89% completed at least five of the six dyadic tasks. This matters because simultaneously placing fNIRS and ECG on young children while preserving enough natural interaction to study co-regulation is methodologically demanding.

The paper therefore offers something more interesting than simply “brain + heart.”

It creates the possibility of asking:

when something happened in the relationship, what was happening simultaneously in the brain, heart, and behavior of each participant?

Neural and cardiac signals do not need to say the same thing

This integration also challenges an important simplification.

Neural synchrony and physiological synchrony are not necessarily redundant indicators of the same process.

The article discusses previous work suggesting that neural synchrony may be more closely associated with communicative signals in some contexts, while cardiac synchrony can track aspects of affect and co-regulation. Studies involving cooperation and competition have likewise found that neural and cardiac coupling can behave differently.

This matters because:

coordination does not necessarily mean becoming the same.

The child may increase activation while the caregiver remains relatively stable.

One participant may anticipate.

The other may respond.

One modality may converge while another diverges.

The authors also emphasize that fNIRS and ECG operate at different temporal scales. Hemodynamic responses require longer windows and lags, while cardiac indices can reflect faster autonomic fluctuations.

Perhaps multiscale dynamics are not merely a methodological inconvenience to be corrected.

Perhaps they are part of the phenomenon itself.

But what state was the relationship in?

Here we can open a BrainLatam window.

Suppose we observe an increase in the child's heart rate.

What does it mean?

By itself, very little.

Did it occur during initial approach?

During uncertainty?

When the caregiver offered help?

During conflict?

During joint problem-solving?

After a behavioral shift in the adult?

The signal becomes more interpretable when we place it inside the trajectory of the interaction.

We can therefore write:

A(t) ⇄ R(t) ⇄ B(t)

where R(t) represents the configuration of the relationship at that moment.

We are no longer studying only two organisms.

We are studying:

two organisms + what is occurring between them + what has already occurred between them.

This is where synchronized video becomes especially valuable.

Not because video “reveals meaning,” but because it helps locate a physiological slice within the relational event.

If the object of study is the relationship, the relationship cannot remain invisible while we measure only its participants.

Baseline is never relationship zero

This becomes even more important in caregiver–child research.

When a dyad enters the laboratory, their relationship already exists.

A period before a task may experimentally be called a baseline, but it does not mean:

R = 0.

The child has already experienced thousands of encounters with that caregiver.

Voice, gesture, rhythm, ways of approaching, comforting, waiting, frustrating, and responding are already part of a relational history.

The experimental present arrives carrying memory.

Recent Brazilian work on land-body-territory among young Quilombola women offers a useful conceptual window: body, memory, affect, biography, and territory appear as intertwined dimensions of experience rather than independent compartments.

That literature does not explain caregiver–child neurophysiology.

But it helps us resist the idea of a body without history.

In BrainLatam terms:

no relational signal reaches a Body-Territory without a past.

Two computers — or two dynamics?

There is also another hidden assumption in the way interaction is often represented:

input → processing → output.

As if A sent a message to B, B processed it, then returned another message.

But the hypothesis of analog cognition recently discussed by BrainLatam permits another framing.

Perhaps relevant aspects of cognition depend on continuous dynamics: frequencies, phases, excitability, propagation, rhythms, gradients, and multiple temporal scales.

In that case, the encounter does not need to wait for a complete “message” to acquire explicit meaning before it starts changing the organism.

A change in prosody.

A facial expression.

A pause.

A movement closer or farther away.

Such differences may modify posture, autonomic activity, attention, and excitability before they can be consciously named.

Thus:

difference may begin transforming the Body-Territory before meaning is fully formed.

The relationship stops looking like a communication channel.

It begins to look like a dynamic:

A₁ ⇄ R₁ ⇄ B₁ → A₂ ⇄ R₂ ⇄ B₂ → A₃ ⇄ R₃ ⇄ B₃.

Brain, heart, lungs — every slice remains a slice

Hong and colleagues integrate fNIRS and ECG, but explicitly note that other experimental designs may incorporate additional modalities, such as accelerometry or eye-tracking, depending on the scientific question. Their physiological acquisition environment can also incorporate respiration.

And we could continue.

Lungs.

Blood pressure.

Movement.

Muscle tone.

Interoception.

Hormones.

Subjective report.

Environment.

History.

The more measures we add, the richer the slice becomes.

But it remains a slice.

What BrainLatam has called the Damasian Mind is useful here precisely because it weakens the idea of an isolated brain merely receiving bodily telemetry. Internal states, homeostatic feelings, interoception, and mappings of the organism participate continuously in felt experience.

We can produce many slices of that mind.

But the Body-Territory is not the sum of our graphs.

The Triple-Aspect Monism proposed by Alfredo Pereira Jr. adds another epistemological caution: matter/energy, information, and sentience can be conceived as inseparable aspects of one reality rather than independent worlds separated merely because our methods measure them separately.

This gives us a simple rule:

Science needs to make cuts. The problem begins when we forget that a cut is still a cut.

ECG is not the relationship.

fNIRS is not the relationship.

Video is not the relationship.

Nor is the sum of all three the entire Body-Territory.

A relationship crosses time

Perhaps the most difficult slice to measure is precisely this one: the accumulated history of the relationship.

Each new encounter finds a relationship already modified by previous encounters.

We might write:

R₁ + encounter₂ → R₂
R₂ + encounter₃ → R₃
R₃ + encounter₄ → R₄.

South American archaeology offers a useful conceptual window here. Babot and Hocsman discuss “artifactual memory”: marks of manufacture, use, modification, and context can be integrated to reconstruct an object's life history.

The analogy must remain cautious — people are not artifacts.

But it helps us think about how a present configuration may carry traces of previous transformations.

And a relationship may continue participating in a Body-Territory even when reciprocity can no longer produce new encounters.

My father, Leixo Cionek, has passed away.

We can no longer produce a new encounter together in which both of us respond and modify one another in real time.

But the encounters we had participated in the construction of the relationship — and also in the construction of the person who now encounters the world without him.

The memory of that relationship is not only what I can consciously recall.

It is also what those encounters have already changed in the Body-Territory that remembers today.

Noé Martínez, an Indigenous Mexican artist, explores in The Body Remembers the relationships among body, ancestry, family history, and memory as a transformed presence in the living body. It is not a neuroscientific explanation. It is another Latin American window onto a related question:

how can what has already passed continue participating in what we are able to encounter now?

So what does it mean to study a relationship?

Hong, Moore, and Quiñones-Camacho take an important methodological step because their protocol allows us to synchronize more precisely when brain, heart, and behavior change during interaction.

Perhaps our next conceptual step is to ensure that the when of the relationship remains as visible as the measured signal.

Before.

Approach.

Formation.

Regulation.

Conflict.

Reorganization.

Ending.

Afterward.

And the history that already existed before the first experimental trigger.

Because:

the meaning of a slice also depends on where that slice appeared in the trajectory of the relationship.

Two brains are not enough.

Two hearts are not enough either.

Measuring more systems brings us closer to the phenomenon, but it does not turn the window into the whole.

Perhaps studying a relationship requires something both simpler and more difficult:

to remember throughout the analysis that our object is not merely two Body-Territories. It is the dynamic history they produce by encountering one another.

Each encounter ends.

But what it transforms may continue encountering time.

References

Hong, Y., Moore, N. J., & Quiñones-Camacho, L. E. (2026). Synchronizing brains and hearts: A practical guide for caregiver–child fNIRS-ECG multimodal hyperscanning. Behavior Research Methods, 58, 199. https://doi.org/10.3758/s13428-026-03060-7
The central paper for this essay. It presents an integrated architecture combining fNIRS, ECG, video, and synchronized tasks for studying caregiver–child co-regulation, including feasibility data with children aged 3–7 and a longitudinal design.

Pereira Jr., A. (2023). Introdução à Metafísica do Monismo de Triplo Aspecto. ANPOF.
Brazilian philosopher and researcher. Proposes matter/energy, information, and sentience as inseparable aspects, offering a framework for avoiding the confusion between a specific measurement and the totality of the phenomenon.

Babot, M. del P., & Hocsman, S. (2023). Decodificando la memoria artefactual desde el sur de Sudamérica. Fortalezas del análisis integral de artefactos líticos. Revista del Museo de Antropología, 16(1).
Argentine archaeologists. Their concept of artifactual memory is used here only as an analogy for cumulative trajectories that leave traces and require multiple lines of observation.

“O nosso corpo ecoou: terra-corpo-território de jovens negras quilombolas” (2024).
Brazilian research articulating body, memory, affect, biography, and territory, helping us think about the Body-Territory as historically situated.

Noé Martínez (2024). The Body Remembers. Rose Art Museum.
Indigenous Mexican artist whose work explores body, ancestry, family history, and memory as dimensions continuously reworked in the present.

BrainLatam (2026). Dynamics — What If Cognition Depends on Analog Computation?
Extends the discussion of analog dynamics toward a multiscale Body-Territory while explicitly distinguishing the BrainLatam hypothesis from the conclusions of the original neuroscience paper.

BrainLatam (2026). Triple-Aspect Monism (Alfredo Pereira Jr.) Expanded: Body, Experience, and Language as a Single Reality.
Connects Triple-Aspect Monism with the Body-Territory hypothesis, emphasizing that physical, informational, and experiential aspects should not be treated as independent realities.

BrainLatam (2026). From the Neuron to the Biome — At What Scale Does Well-Being Begin?
Develops the idea that science may choose different scales from which to observe a phenomenon, provided that the chosen scale is not mistaken for the phenomenon as a whole.