Schumann Ignition Events in Spontaneous EEG: A Conserved Theta–Alpha-Boundary Signature and a Developmental Coupling Gradient

Reported coincidences between Schumann resonances and human EEG date back to König (1974) but have rested almost entirely on averaged spectra, which conflate periodic with aperiodic components, average across state, and cannot resolve whether such coincidences correspond to discrete events in individual recordings. We present an event-level characterization of transient multi-stream coordination events in spontaneous EEG — "Schumann Ignition Events" (SIEs) — across 17 cohort × condition combinations comprising 3,288 subjects and 18,170 events spanning ages 5–88 (six datasets in four countries; the Healthy Brain Network releases supply 77% of subjects), using a four-stream composite detector (envelope × Kuramoto-R × PLV × MSC, envelope band 7.0–8.2 Hz centered at f₀ = 7.6 Hz, S ≥ 1.5).

The paper makes two contributions, and treats the Schumann coincidence as a testable observation rather than a third contribution.

1. A detector and a two-layer frame. The composite detector isolates transient coordination episodes rather than features of an averaged spectrum, generalizing single-threshold burst detection to a multi-stream conjunction. Throughout, we separate architectural claims (population-level features of posterior EEG that randomly placed windows reproduce as well as detected events) from event-conditional claims (visible only when time-locked to events). Conflating the two layers is, we argue, the principal source of over-claim in this literature: it lets a population-mean ratio masquerade as a per-subject lock, and a standing alpha bump masquerade as an event-conditional peak.

2. A conserved theta–alpha-boundary event with a developmental coupling gradient. SIEs show a stereotyped six-phase peri-event architecture (preparatory desynchronization, triple-stream nadir, rebound peak, ~1:4 rise:decay) replicated qualitatively in all 17 cohorts; off-frequency detectors at f₀ = 8.6 and 12.0 Hz reproduce it band-independently, so the architecture is a general property of posterior coordination rather than an SR1-specific phenomenon. The transitions are coherence-first in that a scalp order parameter (Kuramoto R / PLV across channels) leads envelope amplitude by ~1.9 s — a scalp order-parameter lead, not a claim of inter-areal phase coordination, since a companion source-level analysis finds rank-0 cross-territory phase structure (amplitude co-modulation under a shared driver, not propagating phase-locking). Three features are SR1-band-specific. (i) An event-conditional spectral elevation at the theta–alpha boundary near 7.8 Hz, absent from random-window nulls; its cohort-mean centroid (7.687 ± 0.050 Hz) varies by only ~0.35 Hz across the sampled lifespan while individual alpha frequency varies by ~1.8 Hz, and per-subject peaks scatter within the band — so the conserved quantity is a population attractor, not an individual lock. (ii) A boundary-flanking within-event recruitment that targets the SR1 octave alone — the band containing the cavity second mode loses peaks, while SR3, despite sitting near a φ-lattice noble position, elicits none — defeating both a generic "φ-lattice resonance" account and a Schumann-harmonic-class account. (iii) The headline developmental result: cross-subject SR × β amplitude coupling is 3–5× stronger in pediatric than in adult cohorts (shape-weighted ρ = +0.534 to +0.819, p < 10⁻²¹ in all eleven HBN releases independently), preserved under IRASA aperiodic separation (Δρ ≈ +0.19 to +0.29 retained) and continuing as a within-pediatric age gradient. HBN is a transdiagnostic, mental-health-enriched community sample, so absolute coupling magnitudes warrant typical-development replication; the pediatric–adult contrast does not depend on the absolute level. Set against this architecture is a comprehensive null — across cognitive, psychopathological, and diagnostic phenotypes at thousands-of-subjects scale, per-subject event measures track none of them — so the events behave as conserved infrastructure of oscillatory organization rather than as a phenotypic biomarker.

The Schumann coincidence, as a question. The narrowband elevation near 7.8 Hz and a population-stable ~20 Hz beta feature fall in the same neighborhood as the first and third Earth–ionosphere cavity modes. We report this as an empirical observation, show that the φ-adjacent harmonic-ratio structure these events sit within is a relationship among population-mean frequencies rather than a per-subject lock, and treat the coincidence-versus-coupling question as open. Parsimony favors an internal account — there is no established transduction pathway for ELF fields at Schumann-excitation strength, and internal generators at these frequencies are well characterized — and a Faraday-shielded recording with active ELF cancellation is reserved as the dispositive test.

Together these findings constitute a replicable, geometrically specific, developmentally modulated brain phenomenon whose empirical anchoring at the Earth–ionosphere cavity fundamental motivates a focused experimental program rather than a definitive mechanistic claim.