The NERD Model: Why Some Concussion Patients Get Stuck

If you treat concussion patients long enough, you start to notice a pattern.

Some patients improve steadily. Others don’t, and seem to cycle endlessly. Their symptoms fluctuate, the exam findings are persistent, and recovery never really progresses.

They’re not deteriorating.
They’re not failing treatment.
They’re just ... stuck.

That observation was one of the starting points for the model described in “The NERD Model: Reflex Circuit Dysfunction as a Systems-Level Driver of Persistent Post-Concussion Symptoms.” The goal wasn’t to introduce a new label, but to explain a familiar clinical reality: recovery can stall when the nervous system becomes trapped in maladaptive feedback loops.

The Brain Isn’t Broken ... It’s Looping

The NERD model (Network Entrapment by Reflex Dysfunction) frames the brain as a hierarchical control system made up of interacting loops rather than isolated parts.

At a simplified level, these loops include:

• Sensory input loops (visual, vestibular, proprioceptive, interoceptive)
• Reflex loops (brainstem-mediated vestibular, postural, ocular, and autonomic reflexes)
• Modulatory loops (cerebellar timing and gain regulation, basal ganglia–thalamic gating)
• Cortical loops (prediction, perception, cognition, and behavioral output)

In a healthy system, these loops continuously update one another. After concussion, one or more of them can lose flexibility. When that happens, the system may repeatedly return to the same functional state—even when interventions are applied.

That’s the “Groundhog Day” problem in clinical form (in reference to the 1993 movie featuring Bill Murray).

A Concrete Example: Vestibular Reflex Dysfunction

Consider a patient with persistent dizziness, visual motion sensitivity, balance issues, neck tension, and cognitive fatigue.

Traditional approaches often localize this to the vestibular apparatus, the cervical spine, or cortical processing. The NERD model asks a different question:
Which loop is failing to recalibrate?

If someone's cerebellum is injured in a concussion, it has been deomstrated that vestibulo-ocular and vestibulo-spinal reflexes are dysregulated. This causes regression of reflex modulation, resulting in distorted orientation signals continue that ascend through the brainstem. The cerebellum, again, to struggles to normalize timing and gain. This results in noisy signals to the thalamus, and failure to gate noisy input to the cortex. The cortex increases effort, vigilance, cognitive load, decreases metabolic efficiency. The cortex then makes "decisions" based on honest, yet inaccurate input (often termed "compensations"), causing further distortion of (in this example) vestibular signals.

In this scenario, dizziness, tension, visual motion sensitivity, balance issues, and fatigue are not the primary problems—they're the signals that the system has lost its ability to normalize and adapt.

Why This Matters Clinically

The practical value of the NERD model is that it shifts the clinical question.

Instead of asking, “What structure is damaged?”
We ask, “Which loop is entrapped, and what input will facilitate normalization of its function?"

This framework is taught explicitly in the Functional Neurology Management of Concussion Program at the Carrick Institute. Clinicians are trained to:

• Identify dominant dysfunctional loops
• Understand how reflex circuits interact with cerebellar and thalamocortical systems
• Apply targeted interventions aimed at restoring adaptability, not just suppressing symptoms

This is not about doing more techniques. It’s about intervening at the appropriate level of system control.

Bridging Old Neurology and Modern Systems Thinking

One of the strengths of this model is that it does not abandon classical neurology. It builds on it.

The idea of hierarchical organization and loss of adaptive control has deep roots in neurological thought, and much of the clinical philosophy underlying this work traces back to my mentor, Ted Carrick, whose career focused on understanding the nervous system as an adaptive whole.

Equally important is the contribution of my dear colleague and co-author, Dr. Kenneth Jay, whose talent in the ability to formalize clinical observations using modern systems and mathematical reasoning strengthens the model and keeps it disciplined and testable.

An Invitation to Think Differently

This paper doesn’t claim to replace existing concussion approaches. It explains why many of them work—and why they sometimes stop working.

If you’ve ever felt like you were doing your best to treat a concussion patient, they make progress only to regress again, the NERD model offers a way to identify what’s keeping the system locked in place—and how to help it move forward.

That's the work. And this is the invitation.

Please read our publication and share with your networks: https://www.frontiersin.org/journals/systems-neuroscience/articles/10.3389/fnsys.2025.1673195/full

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The NERD Spiral