Can brain–body coupling be measured in a person?
Created with the Levakov et al. (2023) ingest. It is the wiki’s third measurement debate, and it targets the escape route the other two were leaving open.
Why it is a distinct debate and not a corollary
is-the-heartbeat-counting-task-valid asks whether one task works. is-interoception-domain-general asks whether the construct travels across organs. Both have the same implicit remedy running under them: if self-report is the problem, measure the body directly. Heartbeat-evoked potentials, gastric–brain synchrony, respiratory–neural coupling — physiological quantities requiring no judgment, no counting, no confidence rating.
This debate asks whether that remedy works, and the first direct test of it says no. Not because the physiology is unmeasurable — it is, well — but because the coupling between body and brain, which is where the interoceptive content is supposed to live, does not retest.
The finding, and how clean it is
| quantity, same participants, two runs | reliability |
|---|---|
| EGG peak frequency (months apart, different room and equipment) | r = .74 |
| resting-state functional connectivity | strongly within-subject identifiable (t(1033) = 10.89) |
| gastric–brain PLV-delta, within the gastric network | r(21) = −.14, p = .54 |
| gastric–brain PLV-delta, within grey matter | r(21) = −.08, p = .71 |
| node-wise PLV, Schaefer-100 | mean r = .003, ns |
The control conditions are what make this hard to dismiss. A null reliability finding is normally attributable to a noisy instrument; here both instruments demonstrably work in the same participants and the same sessions. The failure is specific to the derived quantity.
The honest brake: n = 23, because reliability required two usable runs and 36 of 59 subjects were excluded. A correlation estimated at n = 23 has wide confidence bounds, and “r = −.14” does not exclude a true r of .2–.3. What it does exclude is a coupling measure strong enough to be a biomarker.
What is agreed
- The gastric network exists. Nobody in this debate disputes it. It survives strict confound regression, generalizes to a new sample and an independent dataset, and has causal support from vagotomy and vagal stimulation.
- Its published extent was mostly artefact. 19.89% of grey matter before confound control, 1.16% after. This is accepted, including by the group whose maps shrank.
- Group-level and person-level claims come apart. Both camps grant that establishing a phenomenon says nothing about whether it can be scored in an individual.
The crux: is r ≈ 0 a fact about the instrument or about the quantity?
| Instrumentation (Kroemer, Müller, and by implication Levakov’s own prescription) | The quantity itself (the sceptical reading) | |
|---|---|---|
| Why reliability fails | Too few gastric cycles (~45 per 15-min run), electrode placement uncalibrated, no respiratory control, PLV-delta compounds noise in two terms | Brain–body coupling may be genuinely state-dependent — varying with hunger, arousal, posture, attention — so there is no stable trait value to recover |
| What would fix it | Longer recordings, high-density EGG, imaging-guided placement, better synchrony estimators | Nothing. You would stop looking for a trait and start modelling coupling as a state |
| Prediction | Reliability rises with recording length; a power analysis exists to be done | Reliability stays near zero however long you record, and coupling tracks manipulable states well |
The second column is not represented by any published author in this debate, which is itself worth noting — the field’s default assumption is that a stable coupling trait is there to be found. But Cao et al.’s hunger-state modulation is direct evidence that coupling moves with state, and a quantity that moves with state is a poor candidate for a trait even when measured perfectly.
These are cheaply distinguishable, and that is the useful thing about this debate: record long, record twice, and plot reliability against recording duration. Nobody has.
What generalizes beyond the stomach
The pattern the wiki now holds three times:
| level | reliable | not reliable |
|---|---|---|
| cardiac perception | — | counting accuracy as perception (is-the-heartbeat-counting-task-valid) |
| cross-channel | confidence (banellis-2026-cross-modal-decorrelation) | cross-channel performance |
| brain–body coupling | the body signal, the brain signal | their coupling |
Three labs, three instruments, three levels. Each individual result is defensible as a local failure; together they describe a field whose components are measurable and whose interoceptive constructs are not. Whether this is one problem or three that rhyme is the reason this page is open rather than a note on another page.
The immediate consequence for reading this wiki: any claim of the form “group X shows altered brain–body coupling” is a group-level claim that cannot currently be decomposed into individual scores — and any claim of the form “coupling predicts outcome Y” is bounded by a reliability nobody has measured for their own instrument.
Why open
Because the reliability datum is one study at n = 23 in one channel; because the causal evidence for the phenomenon is genuinely strong and pulls the other way; because the discriminating experiment (reliability as a function of recording length) is straightforward and unrun; and because the state-versus-trait reading — the one that would make this a permanent rather than a technical limitation — has no advocate and no test.