fNIRS hyperscanning in mother–daughter dyads Fragile X
fNIRS hyperscanning in mother–daughter dyads Fragile X
BrainLatam 2026 commentary on the Research Square preprint rs-7541575/v1
The researcher’s core question is simple, and that’s exactly why it’s powerful: when a girl with Fragile X Syndrome (FXS) interacts live with her mother, does the dyad’s brain-to-brain synchrony (inter-brain synchrony, IBS) look typical—or does it reorganize in a distinctive way—and is that pattern related to how the girl communicates during real conversation? In BrainLatam terms: does “our we” (our Jiwasa) show up in the same places, with the same functional shape, across different social biomes?
To answer that question, the experimental design does something many lab paradigms avoid: it keeps the interaction human. Instead of button presses and isolated stimuli, the study puts mother and daughter into two everyday situations—one with clear rules and shared goal, another with open-ended social timing—and measures both brains at once.
They recruit 63 mother–daughter dyads: 33 with FXS, 18 “control” dyads matched on age and verbal IQ, and 12 typically developing (TD) dyads matched on age. The focus on girls is not cosmetic. It aims to reduce the confounding severity often seen in males with FXS and to examine social-communication organization in a group where diagnosis may be less “obvious” yet still physiologically meaningful.
Now—let’s feel the experiment in our own body for a minute (Mente Damasiana, not as theory but as experience).
You enter a quiet room. Two chairs face each other. You and your mother wear fNIRS caps—snug, slightly strange, like your scalp is being “held.” The researcher says: “Just interact naturally.” Before anything happens, you do 2 minutes of eyes-closed rest—no talking. That alone shifts the state: your jaw loosens, your breath lengthens, your attention drops into the chest and belly. This is a BrainLatam reminder: perception is not an input channel; it is a bodily state. The baseline is not just “control data”—it’s a physiological reset that makes later comparison fairer.
Then comes the first social biome: a cooperative tangram task. You and your mother have 6 minutes to solve patterns that go from easy to hard. Your body changes again: fingers become precise, shoulders subtly rise, breathing gets shallower, the forehead warms—classic Zona 1 tension: instrumental focus to accomplish a goal. You might notice micro-negotiations: who leads, who checks, who holds the frame, who tries a risky move. This is not a flaw; it’s how living systems coordinate.
Here we can bring our observation from complex systems (the flock example): in a murmuration, the flock stays coherent, yet each bird’s behavior differs depending on position—edge, center, front, back—while the collective remains synchronized. That’s exactly the kind of “we” we’re studying here: synchrony with differentiation, not uniformity. In our Jiwasa, roles can split without breaking coherence.
The design includes a clever transition: after tangram, there’s a 2-minute nature video. Not a random “break,” but a deliberate attempt to soften carryover—pull the dyad out of the high-control state so the next task is not contaminated by lingering tension.
Then comes the second biome: guided conversation. The prompt is planning a vacation, supported by questions that help the mother keep the dialogue moving. Feel the shift: now coordination lives in turn-taking, timing, gaze, micro-pauses, and prosody. It’s less “solve the object” and more “co-regulate the space between us.” In APUS/Body-Territory terms, the territory is no longer the table; it is the relational field.
So how does the design measure the researcher’s question—IBS as “our we”?
They use two fNIRS systems (NIRSport2)—one per participant—covering prefrontal, temporal, and parietal regions relevant to executive control, language, and social perception. Data are collected at 7.81 Hz with two wavelengths (760/850 nm), and critically, they include short-separation channels to regress superficial scalp blood-flow effects—important when people are speaking and moving naturally. They apply a conservative pipeline: removing bad channels, checking signal quality, correcting motion (including methods like TDDR and wavelet-based filtering), converting to HbO/HbR, and using short-separation regression to reduce non-neural contamination.
IBS is computed using wavelet transform coherence (WTC)—a method well-suited for natural interaction because it can capture shared rhythmic structure over time—then assessed against a permutation-based null model to identify frequency ranges where dyads synchronize more than chance. That is the design’s direct answer to the first half of the researcher’s question: where and when does brain-to-brain synchrony reliably appear, and how does it differ across groups and tasks?
To answer the second half—whether IBS relates to communication—the design records the conversation and extracts objective speech measures. The audio is transcribed using Whisper and then manually corrected, and language metrics are computed with CLAN/TalkBank tools: MLU (mean length of utterance), TNW (total number of words), WPS (words per sentence), and CPS (clauses per sentence). This matters epistemologically: it keeps us from turning physiology into moral narrative. We have data (IBS) and behavioral structure (language metrics), and we test association without pretending it’s destiny.
What emerges is task-dependent reorganization—again, flock logic.
During the tangram cooperation, dyads in FXS show stronger IBS in right frontopolar cortex, but weaker IBS in left Broca-related regions and right DLPFC compared to controls/TD. In BrainLatam language: the dyad may be sustaining “our we” through a control-monitoring Eu Tensional (Zona 1 reinforced), while showing reduced synchrony in networks that often support fine-grained language-planning alignment during joint action.
During conversation, the FXS dyads show reduced IBS in regions such as left superior frontal, left superior temporal, and left frontal eye fields, and increased IBS in right supramarginal gyrus (SMG). This can be read as a shift in how “our we” is built: less synchrony in parts of the system linked to shared attention/intentional alignment and more synchrony in a phonological/turn-structure anchor. Importantly, girls with FXS show lower MLU and TNW (and lower WPS vs TD), indicating reduced linguistic complexity/fluency in this conversational setting. And the study reports that stronger IBS in right SMG correlates with better language metrics, while also relating to higher social trait severity within FXS—suggesting a functional compensation that is not automatically “health” or “pathology,” but a reorganized strategy.
The design’s strength is precisely this: same dyad, two biomes, objective brain-to-brain metric plus objective language structure, with an attempt to control carryover states. In BrainLatam terms, it helps the reader differentiate bodily state (tension vs fruição), data (IBS values), and narrative (what we think it means), without collapsing complexity into labels.
A next-step question—still aligned with the paper’s ecological spirit—is to pair hyperscanning with direct body-state measures (HRV, respiration, eye-tracking). That would help separate “IBS as social coordination” from “IBS as shared arousal rhythm.” In Zone language: it would clarify when the dyad is locked in Zona 1 control, when it opens toward Zona 2 reorganization, and how “our we” (our Jiwasa) moves across those states—like a flock that stays coherent while roles shift with position in the living territory.
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