Summary: New research presents a unified theory of brain function centered on the idea of criticality — a balanced state between order and chaos that optimizes learning, adaptation, and information processing. When the brain drifts away from this delicate equilibrium, cognitive performance declines and neurological disorders, including Alzheimer’s disease, can emerge.
The researchers report that accumulation of tau protein in Alzheimer’s disrupts criticality, while sleep helps restore it. These findings point to potential new diagnostic tools and therapeutic strategies. Using noninvasive measures such as fMRI to monitor criticality could enable earlier detection and personalized interventions that preserve or recover healthy brain dynamics.
Key Facts:
- Criticality Defined: The brain operates most effectively near a tipping point called criticality, where systems are poised between stability and chaos — ideal for flexible computation and learning.
- Alzheimer’s Connection: Cognitive decline in Alzheimer’s may stem not only from neuron loss but from a breakdown in the brain’s ability to sustain criticality.
- Sleep’s Role: Sleep acts as a restorative process that returns the brain toward criticality, suggesting sleep-based therapies could help prevent or slow neurodegeneration.
Source: WUSTL
Overview
In a paper with implications for preventing Alzheimer’s and other neurological disorders, Keith Hengen, associate professor of biology at Washington University in St. Louis, proposes a comprehensive framework for understanding how brains reach optimal performance. Hengen argues that the brain’s remarkable flexibility and learning capacity emerge from a small set of mathematical principles centered on criticality.
Hengen emphasizes that most brain functions are shaped by experience rather than being prewired at birth. To remain adaptable and able to learn new skills — from reading to driving — the brain needs to stay in a state that supports continual learning. He and co-author Woodrow Shew, a physicist at the University of Arkansas, propose that this state is criticality.
Criticality, a concept from physics, describes a system poised at the boundary between order and chaos. At that edge, information processing, sensitivity to inputs, and the capacity to form and reorganize networks are maximized. The pair argue that brains reach peak computational power when operating near this setpoint.
Physicists first characterized criticality while studying magnets and other materials; later, the concept was applied to avalanches, earthquakes, and complex living systems. A hallmark of critical systems is scale invariance: patterns repeat across levels. In the brain, activity patterns look similar whether measured across a few neurons or entire networks, and across milliseconds or months. This scale-free behavior aligns with how we experience memory and thought, Hengen says.
A new understanding of disease
Applying the criticality framework to neurological disease reframes how we view conditions like Alzheimer’s. Instead of treating them solely as localized damage or accumulation of toxic proteins, this perspective sees disease as a progressive loss of the brain’s ability to maintain the critical setpoint that supports computation.
“Alzheimer’s and other neurodegenerative disorders don’t just kill neurons — they steadily erode the brain’s capacity to compute by dissolving criticality,” Hengen explains. As criticality deteriorates, the brain compensates, masking early dysfunction. That compensation helps explain why patients can appear clinically normal until substantial damage has accrued.
Work with David M. Holtzman at WashU links tau protein buildup directly to disruptions in criticality, connecting molecular pathology to large-scale changes in brain dynamics. This connection raises the prospect that monitoring criticality with tools like fMRI, combined with advanced blood biomarkers, could detect risk long before overt symptoms appear and enable earlier, more effective interventions.
Hengen is also exploring how criticality at birth might predict later cognitive trajectories in children. Early differences in how closely a brain operates near criticality could influence learning potential and developmental outcomes, offering a fresh angle on individual variability in education and cognition.
The sleep–brain link
In early 2024, Hengen and co-author Ralf Wessel examined sleep’s role through the lens of criticality. Longitudinal recordings showed that wakefulness tends to push brain dynamics away from criticality, while sleep restores them. This “reset” function of sleep may be essential for maintaining optimal computation and could be leveraged therapeutically.
Epidemiological and experimental studies already associate poor sleep with elevated Alzheimer’s risk. Hengen and colleagues propose that targeted sleep-based interventions could help restore criticality and improve learning and memory in people at risk or in early stages of disease. In mouse models of Alzheimer’s, sleep-focused interventions that reinforced critical dynamics improved learning performance, offering a proof of concept for translational studies.
Looking ahead
Much work remains to validate and operationalize criticality as a unifying principle of brain function. Hengen envisions a future where measuring criticality helps explain individual strengths and weaknesses — for instance, whether an exceptional artist or scientist exhibits closer tuning to criticality in specific brain regions. Identifying latent capacities through dynamics could reveal hidden talents that need only the right environment to flourish.
Hengen, Shew, and collaborators are sharing their findings widely to encourage dialogue across disciplines. Hengen has presented the idea in public forums, aiming to spark discussion among neuroscientists, clinicians, and the public about how criticality could reshape diagnostics, therapy, and our understanding of the mind.
Washington University’s interdisciplinary environment has supported this work, bringing together expertise from physics, biology, psychology, mathematics, and neuroscience to test and refine the criticality hypothesis.
About this memory, learning, and neuroscience research news
Author: Talia Ogliore
Source: WUSTL
Contact: Talia Ogliore – WUSTL
Image: Image credited to Neuroscience News
Original Research: Open access.
Is criticality a unified setpoint of brain function? — Keith Hengen et al., Neuron
Abstract
Is criticality a unified setpoint of brain function?
Brains evolve under pressures to maximize effective computation through development, plasticity, and homeostasis. The criticality hypothesis proposes a universal operating point around which healthy brains tune themselves: a state of multiscale, marginally stable dynamics that enhances information processing. Over the past two decades, experimental evidence has accumulated in support of this idea, despite debate about interpretation and methods.
In this work, the authors review the theoretical logic, summarize experimental findings, and present a meta-analysis of 140 datasets from 2003–2024. Their analysis suggests that prior controversy often stems from methodological choices rather than true differences in underlying dynamics. The results argue that future research can adopt criticality as a unifying principle to accelerate understanding of behavior, cognition, development, and disease.