What actually happens to the brain during a concussion? Most people think of it as a “bruise,” but that’s not quite accurate. Concussion is a complex functional brain injury involving microscopic disruptions that change how brain cells work — not necessarily how they look.

This blog breaks down the neurometabolic cascade, why symptoms occur, and why rest alone isn’t enough. Note, this is a shorter version of a deep-dive by Mike Bradford. 

The Neurometabolic Cascade

Within milliseconds of impact, the brain experiences a violent shaking or rotational acceleration. This mechanical force stretches brain cells (neurons), disrupting their membranes. As a result:

  • Potassium leaks out of the cells
  • Calcium floods in
  • Excitatory neurotransmitters (like glutamate) are released

This causes a cascade of problems:

  • The brain burns massive energy trying to restore chemical balance
  • Glucose metabolism drops
  • Cerebral blood flow is reduced

This energy mismatch is why even mild stimulation — light, noise, screens — can feel overwhelming after a concussion (1).

It’s a Functional Injury — Not a Structural One

Unlike a fracture or bleed, concussion rarely shows up on CT or MRI scans. The damage is at the cellular level. Think of it like a software bug, not a hardware failure.

Because the injury is invisible, symptoms are the only reliable markers of dysfunction — until we apply objective tests like:

  • Exercise tolerance (Buffalo Concussion Treadmill Test)
  • Oculomotor and vestibular assessments
  • Heart rate variability (HRV) or autonomic screening

Secondary Effects: Inflammation, Dysautonomia & More

In the days and weeks that follow, the brain may also experience:

  • Chronic neuroinflammation
  • Autonomic dysfunction (irregular heart rate, lightheadedness, anxiety)

These issues can prolong recovery and are often responsible for persistent symptoms — especially when concussion is poorly managed early on (2,3).

Clinical Implications

Understanding the pathophysiology of concussion changes how we manage it:

  • Rest alone is not enough. After 24–48 hours of symptom-limited rest, active rehab improves outcomes (4).
  • Every concussion is different. Depending on what systems are affected, treatment may include:
    • Subthreshold aerobic exercise
    • Vision & vestibular rehab
    • Cervical spine therapy
    • Autonomic regulation

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What Patients Need to Know

Concussion is real. And with the right approach, it’s also treatable.

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References
  1. Giza CC, Hovda DA. The neurometabolic cascade of concussion. J Athl Train. 2001;36(3):228–235.
  2. Barlow KM, Crawford S, Stevenson A, et al. Epidemiology of post-concussion syndrome in children diagnosed with concussion in a pediatric emergency department. Pediatrics. 2010;126(2):e374–e381.
  3. Silverberg ND, Iverson GL. Is rest after concussion “the best medicine?” Recommendations for activity resumption following concussion. Rehabil Psychol. 2013;58(3):233–242.
  4. Leddy JJ, Haider MN, Hinds A, et al. Early subthreshold aerobic exercise for sport-related concussion: a randomized clinical trial. Br J Sports Med. 2021;55(22):1265–1272.