Is criticality a unified setpoint of brain function

Is Criticality a Unified Setpoint of Brain Function? — What It Means and Why It Matters

Brains are amazing machines: constantly adapting, stable yet flexible, learning yet able to stay balanced. The recent Neuron article “Is criticality a unified setpoint of brain function?” explores a deep and provocative hypothesis: that healthy brains across individuals and species tend to regulate themselves to a specific computational regime called criticality, and that this might be a core organizing principle of cognition, behavior, and even disease. PubMed+2cell.com+2

Here’s a breakdown of the article’s argument, what evidence supports it, what disagreements remain, and what this might mean going forward.

What Is Criticality?

“Criticality” in this context refers to a dynamical state of neural activity that lies at a boundary between order and randomness (or between stability and instability). The key features are:

• Scale-invariance: Statistical properties of activity look similar at many scales (in space, time).

• Marginal stability: The system is neither so strongly damped that activity dies out quickly, nor so strongly amplifying that it runs away.

• Rich computational capacity: Maximizing information transmission, responsiveness to input, adaptability, etc. PubMed+1

The hypothesis is that criticality isn’t just an occasional or accidental state, but rather a setpoint—something the brain “aims for” via its multiple regulatory mechanisms (development, plasticity, homeostasis, sleep, etc.). PubMed+2BioRxiv+2

What the Paper Does

1. Presents the logic / theoretical case
   The authors argue that since neural systems have many forces pushing them toward extremes (e.g. strong excitation vs inhibition, potentiation vs depression), there needs to be balancing mechanisms. Criticality is proposed as an optimal computational regime: efficient, flexible, responsive. BioRxiv+1

2. Meta-analysis of existing data
   To test how universal criticality might be, Hengen & Shew analyze over 140 (143 in some versions) datasets from studies between ~2003–2024. They examine signatures of criticality, look at methodological differences, and assess consistency. PubMed+1

3. Resolve some controversies
   There has been debate: not all studies find clean “critical” signatures; different measurement or analysis choices lead to different conclusions. The authors show that some of the contradictory findings are due to methodological choices (like how thresholds are defined, what spatial/temporal scales are considered) rather than fundamental differences in the underlying dynamics. BioRxiv+1

4. Make testable predictions and outline implications
   They propose predictions about what should be true if criticality is indeed a unified setpoint: e.g. that deviations from criticality will correlate with impaired cognitive function or disease; that homeostatic mechanisms (including sleep) serve to steer the brain back toward criticality; that this should be observable across species and measurement modalities. BioRxiv+2cell.com+2

What the Evidence Says

The meta-analysis suggests quite a bit of support for the criticality hypothesis:

• Signatures of near-critical dynamics are seen in many species and brain regions. BioRxiv+2PubMed+2

• Across spatial and temporal scales: from micro-electrode/single neuron activity to population/electro-/magneto-/fMRI etc. BioRxiv+1

• In healthy versus pathological states: there is evidence that in disease (neurodegeneration, sleep deprivation, etc.), brain dynamics drift away from criticality. BioRxiv+2PubMed+2

That said, the authors are careful: not every dataset shows perfect criticality; there remain quantitative disagreements, uncertainties about the precise “distance” from criticality in different conditions, and some technical noise / measurement limitations. PubMed+1

What Are the Implications?

If criticality is indeed a unified setpoint, then:

• Understanding of disease could shift: rather than just seeing neurodegenerative disease or disorders as loss of neurons or mis-wiring, part of the problem may be the brain’s inability to maintain or return to critical dynamics.

• Diagnostics & biomarkers: Measuring distance from criticality (via EEG, MEG, fMRI, etc.) might serve as an early indicator of disease or cognitive decline.

• Therapies / interventions: Sleep, neuromodulation, plasticity interventions might be used to nudge brains back toward criticality.

• Cognitive neuroscience and computation: Gives a unifying framework to understand why the brain needs both stability (order) and flexibility (near-chaos), and how it balances these.

Open Questions & Challenges

Even given the promising evidence, there are several open areas:

• What exactly defines “distance from criticality” in practice? How do we reliably measure it?

• Is criticality a single global setpoint or is the brain composed of many local/regional setpoints, perhaps dynamically modulated depending on context (task, rest, disease)?

• How tight is the regulation? How much drift is tolerated before function degrades?

• How do homeostatic, developmental, sleep, and plasticity mechanisms concretely act to maintain criticality?

• How universal is the phenomenon, especially in humans? There are practical limits: measurement resolution, ethics, inter-individual variability.

My Take

This paper is quite exciting. It pulls together a large body of work and tries to argue not just that criticality is a useful metaphor, but perhaps a core organizing principle. If true, that’s powerful, because it gives a simpler lens for thinking about many complex phenomena: learning, adaptability, disease, consciousness.

But I also see that the idea still needs more refined tools: better definitions, more longitudinal human studies, more clarity on causal methods (can we experimentally perturb criticality and observe the predicted effects?).

Closing Thoughts

Brains might not always be “on edge”, but maybe they’re tuned to that edge. Criticality, if indeed a unified setpoint, offers a way to understand how brains are both robust and adaptable, how they handle the tension between order and chaos, and what goes wrong when balance is lost.

As research continues, we might see this become a touchstone concept across neuroscience, medicine, and perhaps even AI. It’s a promising direction—one that gives hope for better diagnostics, better therapies, and better understanding of what makes healthy brain function tick.

Article: Hengen & Shew. Is criticality a unified setpoint of brain function?” 2025. Neuron. August 20, 2025, Neuron, 113, 2582-2598.

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