If you or someone you love has suffered a concussion, you’re probably wondering what exactly a concussion is. A concussion is a type of brain injury that can occur after a blow to the head or body. Concussions can cause symptoms like headache, dizziness, nausea, and problems with thinking and memory. While most concussions will heal on their own within a few weeks, some people may experience long-term effects from their injury. If you or someone you know has suffered a concussion, it’s important to seek medical attention and follow up with a healthcare provider to ensure a full recovery.

What is a Concussion?

A concussion is a traumatic brain injury (TBI), affecting how your brain functions.

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 [1].

What causes a Concussion?

Concussions are caused by a sudden acceleration and deceleration. 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 [1].

When your brain suddenly accelerates inside your skull, the tissues themselves right down to a cellular level get twisted and stretched due to the different 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 or gates 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 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.


  • Headache
  • Neck pain
  • Sensitivity to light/noise
  • Visual problems
  • Dizziness
  • Balance issues
  • Nausea
  • Vomiting

Thinking (cognitive):

  • Memory issues
  • Difficulty concentrating
  • Confusion
  • Feeling slowed down
  • Feeling “in a fog”
  • Trouble thinking clearly


  • Anxiety
  • Nervousness
  • Depression
  • Sadness
  • Irritability
  • More emotional


  • Fatigue
  • 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, this should be considered a suspected concussion and be assessed by a qualified health professional trained in concussion management.

What is a Traumatic Brain Injury?

Traumatic brain injury (TBI) is a term that covers an array of serious physical assaults to the brain. It is one of the most common causes of disability and death in adults. TBIs occur with varying levels of severity, which is seen as a continuum, from concussions on the mild end all the way up to life-threatening and potentially fatal damage across multiple parts of the brain at the severe end. As such, it’s important for individuals to be aware of warning signs and take precautions in order safeguard themselves and those around them in the event of a head trauma.

TBI is a broad term covering three categories: 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’ now being considered synonymous with the term ‘Mild Traumatic Brain Injury’ or mTBI. Although concussions are termed a ‘mild’ TBI, it is important to recognize that the effects of a concussion can be serious!

Mild TBI’s may affect your brain cells temporarily, with no visibile changes noted on medical imaging, while more serious TBI’s result in torn tissues, bleeding and other physical damage that can be seen on imaging. These more severe injuries often result in permanent brain injury and long-term complications or even death due to fatal brain swelling.

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 consciousnessor 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 question 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, which is 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).

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:

Concussion is a mild Traumatic Brain Injury as the classification criteria is identical! The other important point to note is that a concussion is a concussion, and there is no longer any grading scale applied to concussive injuries. This means that you CANNOT have a mild or a severe concussion. Previous grading scales used for concussion are now obsolete as they do not signify severity of injury nor can they quantify 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 concussions actually experience a loss of consciousness following the head injury. Far too often patient’s 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 [1].

The Phases of Concussion

Concussion injuries have two distinct phases.

The initial ‘excitation’ phase, which 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 such as CT’s and MRI’s.

Concussion Recovery

Early intervention of treatment and rehabilitation can help you return to normal brain function and get you back to doing the things you love.

There is a lot of mis-information around concussion injuries, which can make for an often difficult and winding road to recovery. For more information on what to do for a concussion after injury, checkout this post. And, always ensure to follow the guidance of a healthcare provider with training in concussion management.

Complete Concussions is a network of clinics and trained practitioners that provide evidence-based concussion care for all those impacted by concussion. For a comprehensive assessment find a clinic near you today!


Complete Concussions President and CEO Dr Cameron Marshall, explains in detail what a concussion is below: