The Brain’s Best State: How “Criticality” Shapes Learning, Memory, and Neurological Disease
What if the key to unlocking the mysteries of the mind isn’t hidden in complex circuits, but in a delicate balance at the edge of chaos? A groundbreaking new meta-analysis suggests that the brain’s greatest strength — and its greatest vulnerability — may lie in a mathematical principle called “criticality.” This insight could transform how we think about learning, memory, and even devastating diseases like Alzheimer’s.
Note: This article is intended for general information and educational purposes. It summarizes scientific research in accessible language for a broad audience and is not an official scientific press release.
Introduction: A Search for Universal Rules of the Mind
Is the human brain truly the most complex thing in the universe, or could its power come from surprisingly simple rules? In a comprehensive meta-analysis published June 23, 2025, in the journal Neuron, Keith Hengen of Washington University in St. Louis and Woodrow Shew of the University of Arkansas propose a unified theory: the brain’s optimal state may be a fragile balance called criticality, and losing this balance could be fundamental to diseases like Alzheimer’s.
Hengen, as described in ScienceDaily, maintains that the brain’s immense power may originate from relatively simple mathematical principles. If this holds true, understanding criticality could reshape both neuroscience and the future of cognitive health and disease prevention.
What Is “Criticality” — and Why Is It So Important?
Criticality is a concept that originated in physics. When grains of sand are added to a pile, the pile grows steeper until, at a certain point, it becomes unstable and avalanches. That tipping point — right before chaos — is referred to as the critical point. At this stage, the system is maximally sensitive, flexible, and ready to adapt to changes.
According to Hengen and Shew, the brain operates in a comparable manner. They suggest that brains need to reach criticality in order to think, remember, and learn. In this state, the brain is neither too rigid nor too chaotic but perfectly positioned to process information, adapt, and learn from experience — a kind of sweet spot for cognition.
This principle could help explain why the brain is remarkably adaptable, creative, and resilient, as well as why significant consequences arise when this balance is lost.
The Science Behind Criticality: From Sand Piles to Synapses
The concept of criticality was first used to describe physical phenomena like magnets and earthquakes. Later, physicists realized it could be applied to any complex system, including living brains. One key feature of such systems is scale-invariance: similar patterns emerge whether observing a handful of neurons or the entire brain, over milliseconds or months.
Hengen emphasizes that internal human experiences also lack a set scale, which aligns with these neuroscientific observations. Brain activity demonstrates recurring patterns across many scales, supporting the idea that criticality may be a unifying principle of brain function.
In their meta-analysis, Hengen and Shew reviewed more than 140 scientific studies published between 2003 and 2024. These studies included animal models and human brains, multiple brain imaging methods, and various states such as sleep, wakefulness, and anesthesia. Their aim was to determine if criticality genuinely acts as the brain’s setpoint for optimal function.
Why Does the Brain Need Criticality?
Most human abilities are learned rather than pre-programmed. From walking to speaking to solving complex problems, the brain must be ready to adapt to new experiences throughout life. But how does a network of billions of neurons and trillions of connections remain so flexible?
Hengen and Shew suggest that criticality is the underlying answer. At this state, the brain is highly sensitive to new information, flexible, efficient in its use of energy and resources, and capable of complex processing across all levels and timescales.
In their view, criticality is what makes the brain a learning machine. If researchers can understand how the brain maintains this state — and what occurs when it is lost — this may unlock new approaches to support learning and brain health throughout life.
Measuring Criticality: A Mathematical Approach
Hengen and Shew emphasize that criticality can be measured using mathematical tools. They have developed methods for estimating how close a brain or brain region is to the critical state, using technologies such as functional MRI (fMRI).
According to their statements in ScienceDaily, they believe these mathematical approaches can help address fundamental questions about human brain function. This development may lead to new ways to diagnose and monitor brain health, potentially even before symptoms are apparent.
Criticality and Disease: A New Way to Understand Alzheimer’s
When the brain loses its critical balance, Hengen and Shew argue that this may be at the root of many neurological disorders, including Alzheimer’s disease.
Historically, Alzheimer’s research has focused on damaged neurons or toxic protein accumulation. The new framework proposes that the most profound effect of such diseases is to disrupt criticality. Hengen states that neurodegenerative diseases do not just damage neurons but undermine the brain’s overall computational ability by eroding criticality. As the brain moves further from this optimal state, its capacity to adapt, learn, or recover diminishes.
This perspective helps explain why individuals with early-stage Alzheimer’s can often function normally for years, even as brain changes accumulate. The brain compensates, but as criticality deteriorates, cognitive symptoms eventually emerge — often after the underlying changes have been developing for a long time.
Diagnosing Diseases Earlier: The Promise of Criticality-Based Tools
Through collaboration with David M. Holtzman, MD, at WashU Medicine, Hengen has shown a direct link between tau protein buildup (a hallmark of Alzheimer’s) and loss of criticality. This suggests that tracking criticality in the brain could enable much earlier identification of brain health changes — potentially years before symptoms develop.
Hengen maintains that combining such measurements with advanced blood tests could help identify people at risk and allow for interventions before irreversible damage occurs. If criticality can be measured non-invasively, for example with a brain scan, it might one day become part of routine cognitive health assessments.
As reported in ScienceDaily, this connection between criticality and Alzheimer’s opens new diagnostic possibilities. Theoretically, a simple fMRI could help detect breakdowns in criticality years ahead of any symptoms.
Criticality Across the Lifespan: From Infants to Artists
The implications of this theory go beyond aging. Ongoing research by Hengen and colleagues investigates whether criticality at birth can predict a child’s future learning abilities. Hengen suggests that children who are closer to criticality from the outset are likely to be better learners. While many factors influence academic success, criticality may explain much of the variation between children.
Hengen also speculates that individuals with exceptional creative or cognitive talents might have brain regions especially close to criticality. In his view, a person with extraordinary artistic ability, for example, may exhibit criticality in the brain regions related to creative ideation.
The Sleep-Mind Connection: Sleep as a Reset Button
Recent studies by Hengen and his colleagues indicate that being awake and active shifts the brain away from its optimal state of criticality, while sleep acts as a reset, restoring this balance.
This insight may help explain the critical role of sleep in memory and learning, as well as the increased risk for Alzheimer’s seen in individuals who do not get enough quality sleep. Experimental work in mice indicates that targeted sleep interventions can restore criticality and improve learning, potentially slowing the course of brain disease.
As summarized in ScienceDaily, mice bred to exhibit symptoms of Alzheimer’s became faster learners after a sleep intervention that reinforced criticality.
Why Does This Matter? A New Blueprint for Brain Health
If criticality truly represents the brain’s optimal state, as Hengen and Shew propose, then measuring it could enable much earlier detection of brain disorders — well before clinical symptoms appear. New therapies might one day be designed to restore or maintain criticality through interventions such as sleep regulation or cognitive training.
Additionally, educational strategies and approaches to child development could be personalized according to each individual’s unique brain state, and targeted interventions could help aging brains maintain learning and memory for longer.
Hengen emphasizes the importance of collaboration across disciplines and envisions a future in which a unified theory of the mind brings together expertise from fields such as physics, biology, psychology, mathematics, and neuroscience.
The Road Ahead: Challenges and Future Directions
While the theory of criticality is promising, further research is needed. Hengen and Shew’s work calls for more studies that directly test the criticality hypothesis in humans and the development of practical tools for measuring criticality in clinical settings. Nevertheless, many in the neuroscience community recognize the potential of this new direction.
Hengen hopes that their work will encourage cross-disciplinary cooperation and eventually bring new hope to people living with brain disorders. He remains optimistic that acceptance of the criticality theory will continue to grow within the scientific community.
Original Research and Further Reading
- Hengen, K.B., Shew, W.L. (2025). Is criticality a unified setpoint of brain function? Neuron, 113, 1–17. DOI: 10.1016/j.neuron.2025.05.020
- “The brain’s sweet spot: How criticality could unlock learning, memory — and prevent Alzheimer’s” ScienceDaily: https://www.sciencedaily.com/releases/2025/06/250625075016.htm
The information in this article is provided for informational purposes only and is not medical advice. For medical advice, please consult your doctor.
