"Over 80% of the brain's neurons are located in the cerebellum."

• The human cerebellum contains 69 billion neurons out of 86 billion total brain neurons (B1, B2 — Herculano-Houzel 2009, PMC2776484; both quotes verified live on the source page).
• Computed percentage: 80.23% — strictly greater than the 80% threshold (by 0.23 pp).
• Two independent peer-reviewed sources (B3, B4) state the cerebellum holds "about 80%" of brain neurons, cross-checked against the computed value (within 2 pp tolerance).
• All 4 citations verified live with full-quote match. No citation fallback required.

Natural language: Over 80% of the brain's neurons are located in the cerebellum.

Formal interpretation:

Operator rationale: "Over 80%" is interpreted as strictly greater than 80.0%. If the cerebellum held exactly 80.0%, the claim would be FALSE. This is the more conservative reading; using ≥ would make the claim easier to prove. "Brain" means the entire brain (cerebrum + cerebellum + brainstem) excluding the spinal cord — the standard neuroanatomical usage in all cited sources.

Source: proof.py JSON summary

Linked Sources

The primary neuron counts come from Herculano-Houzel (2009), a peer-reviewed review in Frontiers in Human Neuroscience (PMC2776484) that synthesizes the landmark isotropic fractionation study by Azevedo et al. (2009):

• Total brain neurons (B1): 86 billion — parsed from the quote "the adult male human brain, at an average of 1.5 kg, has 86 billion neurons and 85 billion non-neuronal cells"
• Cerebellum neurons (B2): 69 billion — parsed from "the human cerebellum, at 154 g and 69 billion neurons, matches or even slightly exceeds the expected"

Both data values ("86 billion neurons", "69 billion neurons") were confirmed to appear verbatim on the live page.

The computed percentage (A1):

69,000,000,000 / 86,000,000,000 × 100 = 80.2326%

This exceeds the 80% threshold, so the claim holds: SC1 (80.23% > 80%) = True.

Two independent sources corroborate this figure:

• B3 (von Bartheld et al. 2016, PMC5063692) — a major review of 150 years of cell-counting methodology — states: "the cerebellum (which contains about 80% of all neurons in the human brain; Azevedo et al. (2009))"
• B4 (Herculano-Houzel et al. 2010, Frontiers Neuroanatomy) — a cross-species comparative study — states: "the cerebellum holds … 80% in the agouti, galago, and human"

Both independently agree within 2 percentage points of the computed 80.23% (cross-check tolerance satisfied).

Verdict: PROVED

The human cerebellum contains 69 billion of the brain's 86 billion neurons — 80.23% — which is strictly greater than 80%, as confirmed by: - Live-verified raw counts from a peer-reviewed PMC source (B1, B2) - Two independent peer-reviewed sources stating "80%" (B3, B4) - All four citations fully verified (tier 4–5 sources)

Important caveat: The margin is thin (0.23 pp), and the measurement uncertainty in the underlying Azevedo et al. 2009 study (±8–9% on neuron counts) is larger than this margin. The scientific literature consistently characterizes the figure as "about 80%" rather than "strictly over 80%." Under the dominant methodology the claim is TRUE, but a competing estimate (Andrade-Moraes 2013) yields ~63%, which would disprove it.

1. Competing methodology (Andrade-Moraes et al. 2013): The PMC5063692 review (Table 4) lists an alternative estimate of 54 billion cerebellar neurons from Andrade-Moraes et al. (2013) — 22% lower than Azevedo's 69 billion. Using 54B of an assumed 86B total yields ~62.8%, well below 80%. This is a genuine methodological dispute. However, Azevedo et al. 2009's isotropic fractionation method is the current gold standard and is cited universally in reviews and neuroscience education. No peer-reviewed paper argues the cerebellum holds ≤80% under the Azevedo methodology.

2. Popular-science understatement: brainfacts.org (2020) states the cerebellum contains "more than half of its neurons" — a much lower claim. This is a popular-science source, not a peer-reviewed estimate, and does not contradict the quantitative finding.

3. Spinal cord inclusion: The human spinal cord contains ~1 billion neurons. Including it raises the total to ~87 billion: 69/87 = 79.3%, just below 80%. However, "brain" in neuroanatomy excludes the spinal cord by definition, and all cited sources use this convention.

4. Thin margin (0.23 pp): The computed excess over 80% is only 0.23 percentage points. Azevedo et al. 2009 report uncertainty of ±8.1B for total neurons and ±6.65B for cerebellum neurons — the margin is within measurement error. The scientific literature consistently rounds to "about 80%" without claiming strictly greater. This is a genuine limitation: the proof rests on point estimates, not a confidently strict threshold. The verdict is PROVED on the point estimates as reported, with this caveat noted.

5. Linguistic interpretation: "Over 80%" means > 80.0% in standard English. The computed 80.23% satisfies this.