Levakov, Ganor & Avidan (2023) — Reliability and validity of brain-gastric phase synchronization
The wiki’s first gastric evidence of its own, and it arrives as a methods audit rather than a discovery. Three ingests have now cited the stomach at second hand — Banellis et al. put stomach at the top of the brain-constrained CCA loadings (0.58) for body-wandering; Bonaz et al. built a clinical chapter on brain–gut interaction; the domain-generality debate names gastric as “the notable absence, since it is where coherence was originally claimed.” This paper is the first source here that actually measures a stomach.
What it finds is a two-part verdict that is worth keeping separate, because the paper’s abstract runs them together and its citations will not.
Part one: the network is real, and it was four-fifths noise
Rebollo et al. (2018) reported a resting-state network phase-locked to the stomach’s ~0.05 Hz myoelectrical rhythm — a genuinely novel kind of finding, an intrinsic brain network defined not by its own dynamics but by an organ’s. It has been elaborated since: unimodal rather than transmodal cortex (Rebollo & Tallon-Baudry 2022), modulated by vagus nerve stimulation (Müller et al. 2022).
None of that work regressed head motion. This one does, along with global signal, non-grey-matter signal and cardiac RETROICOR components, and the result is the paper’s single most quotable number:
| significant voxels | % of grey matter | |
|---|---|---|
| minimally preprocessed | 25,504 | 19.89% |
| strict confound regression | 1,491 | 1.16% |
Nearly a fifth of grey matter appeared coupled to the stomach before cleaning. What survives — occipital, precuneus, bilateral insula, pre/postcentral — is spatially concordant with the published network above a spin-permutation null, so the phenomenon is not an artefact. But its published extent largely was, and the claim “the stomach is coupled to a wide swathe of cortex” has to be withdrawn to something much narrower.
The mechanism is the interesting part. These confounds are not incidentally present; they are synchronized with the EGG signal itself — CSF, global signal, and three of six motion parameters. The paper’s proposed route is respiration, which moves the head and modulates gastric signal alike, and whose frequency band can bleed toward the gastric one. It has no respiratory recording to check this with, which is the paper’s sharpest self-inflicted limitation and a standing lesson for respiratory-interoception: breathing is a confound in every other interoceptive channel’s measurement, not merely a channel of its own.
Part two: the coupling has no test–retest reliability, and this is the finding that matters
Two runs, same subjects, same session. The correlation between run 1 and run 2 gastric–brain synchrony:
- within the significant gastric network: r(21) = −.14, p = .54
- within the grey-matter mask: r(21) = −.08, p = .71
- node-wise across Schaefer-100 parcels: mean r = .003, not different from zero
Zero, twice, three ways. And the control analyses close off the easy dismissal: the EGG peak frequency of the same people correlated r = .74 across recordings taken months apart in different rooms on different equipment, and resting functional connectivity was strongly subject-identifiable. The stomach is a reliable measurement. The brain is a reliable measurement. The relationship between them, as currently operationalized, is not a property of the person.
The consequence is stated in the paper via Goodwin & Leech (2006) and it is the general principle, not a gastric one: reliability bounds validity. A measure that does not correlate with itself cannot correlate with hunger, with symptom severity, with eating pathology, or with anything else. Every individual-differences use of gastric–brain coupling — including the first author’s own 2021 paper predicting weight loss from brain–gastric interaction (Levakov et al., NeuroImage 224:117403) — is under this ceiling.
That self-implication is why the paper is worth trusting. The authors published a result that undercuts their own prior finding, and say so obliquely by citing it in the discussion as the kind of work that “will allow future work to explore the functional significance.”
Why this matters beyond the stomach
The wiki now holds three independent instances of one pattern, and they should be read together:
| channel | what is reliable | what is not |
|---|---|---|
| cardiac | — | heartbeat counting as a perceptual measure (is-the-heartbeat-counting-task-valid; <10% can do it, van-der-does-2000-heartbeat-perception-reanalysis) |
| cardiac ↔ respiratory | confidence (r ≈ .51–.64) | cross-channel performance (banellis-2026-cross-modal-decorrelation) |
| gastric ↔ brain | the EGG signal (r = .74), the fMRI signal | their coupling (r ≈ 0) |
Three different labs, three different instruments, three different levels of analysis, and the same shape each time: the components are measurable and the interoceptive quantity built from them is not. This is now sufficiently repeated that it should be treated as a property of the field’s measurement programme rather than a series of local failures — see is-brain-body-coupling-a-reliable-individual-difference, created with this ingest.
It also sharpens what banellis-2026-body-wandering can be taken to have shown. That study reported “convergent patterns in respiration and electrogastrography” alongside its body-wandering dimension. Nothing in Levakov et al. touches EGG measurement itself — which is reliable — so the signal-level claim stands. What would not stand is a follow-up correlating body-wandering with gastric–brain coupling, and that is the obvious next study for that group.
What it does not say
It does not say the gastric network is spurious. The authors are explicit that it generalizes, that rodent vagotomy work (Cao et al. 2022) and human taVNS (Müller et al. 2022) supply causal support neither of which can be explained by motion, and that group-level gastric–brain coupling is a robust phenomenon. The distinction the paper insists on and this wiki should preserve:
- Group-level existence: established.
- Individual-level measurement: not yet a thing that can be measured.
The second is what a biomarker requires. Petzschner et al. already conceded that the computational-biomarker programme “has almost no empirical test behind it”; this is what one of those tests looks like when it is run.
Provenance notes
Open access (CC-BY), Israel Science Foundation funded, data and analysis code public (github.com/GidLev/brain_gastric_synchronization_2023). The authors thank Rebollo and Tallon-Baudry for sharing code and maps — i.e. the group whose finding this paper trims did the trimming with them, which is a better sign about this literature than most. Nicolas Legrand and micah-allen’s Systole package supplies the cardiac peak detection, connecting this paper’s toolchain to the Aarhus group whose work occupies the wiki’s other recent ingests. No researcher page created for Levakov, Ganor or Avidan: single appearance in raw/, per the wiki’s convention.