What is a Concussion?
A concussion is a traumatic brain injury, otherwise known as a TBI, affecting how your brain functions. There are three categories of TBI: Mild, moderate, and severe. It was previously thought that Concussion was a separate category that sat prior to the mild TBI category. However, Brain Injury is viewed as a continuum of injury, with the term ‘Concussion’ being synonymous with the term ‘Mild Traumatic Brain Injury’ (mTBI). Although concussions are termed a ‘mild’ traumatic brain injury, it is important to recognize that the effects of a concussion can be serious!
Traumatic brain injuries are categorized by the Glasgow Coma Scale or GCS, which is a reliable measure of a person’s level of consciousness post-injury. Categorization is also based on the length of time someone may have experienced post traumatic amnesia (PTA) and/or loss of consciousness (LOC).
The GCS is rated numerically from 3 to 15, where 15 is indicative of someone who is completely awake and fully alert. A concussion is classified as a GCS of 13 to 15; meaning there may be some transient confusion, but for the most part the person is conscious, alert and lucid. It is important to be aware that after a concussion injury, there may be NO loss of consciousness, or there could be a loss of consciousness of up to 30 minutes. If the loss of consciousness is longer than 30 minutes, this would be considered a moderate to severe traumatic brain injury.
Post traumatic amnesia (PTA) following concussion is termed ‘anterograde amnesia’; which is the inability to form new memories. This is the person who continues to ask the same questions over and over again; they know who they are, where they live and everything that happened in the past. What they don’t recall is things they have been told between the accident and now; for a concussion this last for less than 24 hours.
The below table highlights the differential categorization of more significant brain injuries such as moderate and severe TBI’s in direct comparison to concussion or mild TBI. The table also notes findings that may be seen on imaging. For a concussion (a FUNCTIONAL rather than a STRUCTURAL injury), imaging is typically unremarkable as there is no observable structural brain pathology (ie. a brain bleed, which would be considered a structural change to the brain).
So, Concussion is a mild Traumatic Brain Injury as the classification criteria is identical! The other important point to note is that all concussions fall into this category and there is no longer any grading scale for concussive injuries. This means that you CANNOT have a mild or a severe concussion. The previous grading scales used for concussion are now obsolete as they do not signify severity of injury nor do they mean anything in terms of prognosis or recovery time. You CANNOT accurately classify or grade a concussion based on severity!
What’s really important to understand, is that only approximately 10% of patients actually experience a loss of consciousness following a concussion. Far too often a patient will be told that if they didn’t lose consciousness then they don’t have a concussion. But that is simply NOT true. The data doesn’t lie: 90% of concussions DO NOT result in a loss of consciousness .
With all this being said, the question still remains …
What is a Concussion?
Concussion has been defined as “a traumatic brain injury induced by biomechanical forces” by the International Consensus Statement for Concussion in Sport, which is the guiding document developed by the Concussion in Sport Group . But again, you might ask what does this actually mean?
We discussed above the continuum of traumatic brain injury; the biomechanical forces mentioned in the definition refer to the sudden acceleration and deceleration forces required to cause a concussive injury.
Despite the common misconception that a concussion occurs due to a hit to the head, what actually causes a concussion is the rapid acceleration of the brain inside the skull. This acceleration may result from a hit to the head, face, neck or elsewhere on the body with forces transmitted to the brain .
When your brain suddenly accelerates inside your skull, the tissues themselves right down to a cellular level get twisted and stretched due to the differing densities or weights that make up the tissues of your brain.
Stretching of your brain nerve cells (the electrical circuitry or communication system of the brain), causes a chemical change to occur. Put simply, some of the molecules outside swap over with some of the molecules inside the cell due to the opening of tiny channels in the cell membrane or its exterior surface. This exchange results in your brain cells becoming “excited”, which is how the cells in a normal state communicate and pass messages along. For example, for your arm to move, many cells need to pass a message along from the brain to the arm, connecting with the correct muscles and resulting in the arm lifting in the direction intended.
In the event of a concussion, excitation does not occur in the same orderly manner as normal messages and also without the same meaningful intention. Instead, the resulting excitation may affect multiple areas at once, causing many mixed and unintentional messages. This excitation event essentially results in some of the immediate signs and symptoms of concussion such as blank vacant stare, stepping and stumbling, incoordination and more.
A more exhaustive list of the signs and symptoms of concussion is included below.
- Neck pain
- Sensitivity to light/noise
- Visual problems
- Balance issues
- Memory issues
- Difficulty concentrating
- Feeling slowed down
- Feeling “in a fog”
- Trouble thinking clearly
- More emotional
- Low energy
- Sleeping more or less
- Difficulty falling asleep
Remember, each concussion case is different. And, if you experience any ONE or MORE of the following symptoms after a significant impact to the head or body, then you should suspect a concussion and be assessed by a qualified health professional trained in concussion management.
Concussion signs and symptoms are often rapidly seen and felt; however, this is not always the case and symptoms may evolve overtime.
There are some specific signs that should be watched for following a concussion injury. These warning signs are known as RED FLAGS and can be indicative of more serious and potentially life-threatening conditions. Go straight to the nearest emergency department if you experience any of the following:
Phases of Concussion
Concussion injuries have two distinct phases.
The initial ‘excitation’ phase uses a lot of energy in the brain, meaning that in the following hours to days there is a reduction in brain energy levels commonly termed the ‘spreading depression’ phase.
This secondary phase is often accompanied by further symptoms such as drowsiness and extreme fatigue. After reaching a peak low in brain energy stores at approximately 5 days post injury, energy levels are gradually restored to normal.
Studies have shown this energy recovery can take anywhere between 22 to 45 days post injury [2,3,4]. The biggest risk is that most people will generally feel better between 7 to 10 days and the brain remains highly vulnerable until energy levels have been fully restored. As such it is important to ensure full recovery from a concussion has been achieved prior to being cleared to return to sport.
In summary, concussion is a temporary injury occurring due to an acceleration / deceleration force to the head, neck or body, resulting in a transient change in brain FUNCTION. As a functional injury, concussions do NOT damage the structure of the brain, and as such will not be evident on structural brain scans or imaging.
Early intervention of treatment and rehabilitation can help you get back to doing the things you love. Always ensure to follow the guidance of your healthcare provider.
Complete Concussion Management is a network of clinics and trained practitioners that provide evidence-based concussion care for all those impacted by concussion. We may have a clinic near you.
Complete Concussion Management President and CEO Dr Cameron Marshall, explains in detail what a concussion is below:
 McCrory, P., Meeuwisse, W., Dvorak, J., Aubry, M., Bailes, J., Broglio, et al. (2017). Consensus statement on concussion in sport: the 5th international conference on concussion in sport held in Berlin, October 2016. British Journal of Sports Medicine. 0:1–10. doi:10.1136/bjsports-2017-097699
 Signoretti, S: Marmarou, A., Tavazzi, B., Lazzarino, G., Beaumont, A., & Vagnozzi, R. (2001). N-Acetylaspartate reduction as a measure of injury severity and mitochondrial dysfunction following diffuse traumatic brain injury, Journal of Neurotrauma, 18(10), 977-991.
 Vagnozzi, R., Signoretti, S., Tavazzi, B., Floris, R., Ludovic, A., Marziali, S. et.al. (2008). Temporal window of metabolic brain vulnerability to concussion: a pilot 1H-magnetic resonance spectroscopy study in the concussed athletes-part III. CORD Conference Proceedings. 62 (6), 1286-6.
 Vagnozzi, R., Signoretti, S., Cristofori, L., Alessandrini, F., Floris, R., Isgro, E. et.al. (2010). Assessment of metabolic brain damage and recovery following mild traumatic brain injury: a multicentre, proton magnetic resonance spectroscopic study in concussed patients. Brain. 133(11), 3232-3242.
This information is designed to provide education and awareness. This article is not intended as a substitute for the medical advice of doctors and/or healthcare professionals. The reader should always consult their physician and/or healthcare providers in matters relating to their health, and in particular, with respect to any concussion and/or symptoms that may require diagnosis or medical attention.