How Mild is Mild? Concussion and mild-Traumatic Brain Injury

I’ve been playing sports since the time I could walk. I played three sports competitively in high school and even got recruited to play soccer at Colby College. As a goalie, I had been lucky in that I had never dealt with any injuries. Sure, I’d collide with a striker here and there and end my games with some funky looking bruises, but I’d never sustained anything that serious. In my fifth collegiate soccer game, all of that changed.

Early on in the second half, a forward was on a break away coming right at me. I came off my goal line, got low and approached the forward, trying to break up the play. All of a sudden I was flat on the ground. I had saved the shot with my jaw. My head was ringing and my lip felt swollen, but I was convinced I was fine. My trainer came out, talked to me, and I insisted I was fine. But I was the furthest thing from fine.

That night, I couldn’t look at a screen without developing an excruciating headache. I had a hard time focusing and couldn’t really maintain a conversation without feeling drained. The next day, I felt like a vampire because the sun was absolutely unbearable. My trainer kept me out of our next game, and after a physical examination and a very poor performance on the concussion test I was diagnosed with a concussion.

A concussion is the mildest form of a mild-traumatic brain injury (mTBI) and occurs when a head injury triggers an immediate change in mental status [2]. Although concussion and mTBI are used synonymously, it is important to note that while all concussions are 


mTBIs, not all mTBIs are concussions. In the U.S., between 1.6 and 3.8 million sports related concussions occur each year [1]. These numbers are pretty staggering, but the true incidence of sports related concussions is likely much higher because a lot of concussions go unreported and are not evaluated in a clinical setting [1].  One might think that, given the high prevalence of concussions in our country, there would be one standardized protocol or set of diagnostic criteria set in place. However, this is not necessarily the case.

When I sustained my concussion in a collegiate soccer game, my athletic trainer likely followed the protocol set in place by the American Medical Society for Sports Medicine. This protocol is a multifaceted approach that uses a few tools to generate a diagnosis: a self-report symptom scale, computerized neurocognitive testing, balance and postural testing, and a physical examination [3]. I essentially filled out a sheet that asked me to rate the presence and severity of my symptoms, completed the IMPACT test (a computerized test assessing my visual and spatial memory, reaction time, and executive functioning) and did a series of balance tests. The results of this battery of tests were significantly different from my baseline testing, leading my athletic trainer and the physician at Colby to diagnose me with a concussion. After a few weeks of bothersome headaches, dizziness, and extreme emotional dysregulation, it seemed as though all of my symptoms were gone and I was cleared to return to soccer.


The Glasgow Coma Scale (

But what if I did not sustain my concussion in a soccer game at Colby? What if I were in a motor vehicle accident on my way up to Colby? Motor vehicle accidents are one of the leading cause of mild-traumatic brain injuries in adults [4]. If I had been in a serious car accident, I likely would have been met at the scene by EMTs and taken to the closest Emergency Room. Perhaps the physicians in the Emergency Department would have used the concussion diagnostic criteria established by the World Health Organization (WHO) [4]. Following this protocol, the doctors would have used the Glasgow Coma Scale (GCS), a scale that helps doctors measure eye opening response, verbal response, and motor response after a head injury [5]. A score of 13-15 on the GCS indicates a mTBI, while lower scores indicate more serious head injuries [5]. Let’s say that I was evaluated by an emergency room doc and that my GCS score was a 14. In this case, I would have also been diagnosed with a concussion. My symptoms could have lasted for up to six months following this injury [2], much longer than the two weeks that I had symptoms from my sports related concussion.


The two injuries described – a sports related concussion and a concussion from a motor vehicle accident- differ in injury severity, symptom severity, diagnosis protocol, and management. Yet, they share the same diagnosis: a mild-traumatic brain injury or concussion. These two very different cases with the same diagnosis raise a few important questions. First, should the terms “concussion” and “mTBI” be used synonymously? And secondly, how can we learn more about the most mild of the mild injuries?

rats and soccerOne way to study the mildest type of mTBI is to study animal models for concussion. In the last few decades, several animal models of concussion have been established. A nice review of these methods can be found here. Though these models are useful in studying the consequences of head injury, many of the animal models for concussion do not give us the full picture of how a human sustains a concussion. One new method to induce concussion in rodents was established by the Glenn Lab in 2017 [7].  In this model, rodents are strapped into a rotating arm and dropped in an attempt to recreate a truly mild injury as it occurs in humans. Models like this enable us to really study the behavioral and biological outcomes of the mildest type of head injury.


  1. D.H. Daneshvar, C.J.  Nowinski, A.C. McKee, R.C. Cantu. The epidemiology of sport-related concussion. Clin Sports Med. 2011;30(1):1-17, vii.
  2. W.J. Mullaly. Concussion. The American Journal of Medicine , Volume 130 , Issue 8 , 885 – 892
  3. A.R. Mayer, D.K. Quinn, C.L. Master. The spectrum of mild traumatic brain injury. Neurology Aug 2017, 89 (6) 623-632; DOI:10.1212/WNL.0000000000004214
  4. RC Gardner, K Yaffe . Epidemiology of mild traumatic brain injury and neurodegenerative disease. Mol Cell Neurosci. 2015;66(Pt B):75-80.
  5. G. Teasdale, B. Jennett . Assessment and prognosis of coma after head injury. Acta Neurochir 1976; 34:45-55.
  6. I. Cernak . Animal models of head trauma. NeuroRx. 2005;2(3):410-22.
  7. P Wirth, W Yu., A.L. Kimball, J. Liao, P. Berkner, M.J. Glenn. New method to induce mild traumatic brain injury in rodents produces differential outcomes in female and male Sprague Dawley rats. Journal of Neuroscience Methods, Volume 290 (2017). pp. 133-144,

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