What is concussion?


For athletes in contact sports, a knock to the head used to be seen as little more than a temporary inconvenience, an occupational hazard. What exactly is concussion, how do you know if you have it, and what should you do to recover from it?


How blows to the head and other impacts can cause concussion.
How blows to the head and other impacts can cause concussion.
Levent Efe / The Queensland Brain Institute

What causes concussion?

The brain floats inside the skull, suspended within a protective cushion of cerebrospinal fluid. A direct blow to the head, face or neck, or from an impact to somewhere else on the body, can create a force that shakes the brain. When that force is strong enough, or comes from a particular direction, the brain can move so that it strikes the skull or twists upon itself. Just as for any body part that is struck, bruising and cell damage can occur. When those cells are neurons, however, concussion is the outcome. Because the brain is so central to our lives, controlling mood, perception and movement, the effects of concussion can be far-reaching.

Who is most at risk from concussion?

The connection between contact sport and concussion has been widely publicised. In the general population, however, concussion is in fact extremely common. Typically caused by a fall or car accident, it can also be sustained by a wide variety of other activities.

The outcome of a blow to the head can be either mild or severe. While anyone who has been ‘knocked out’ has usually suffered concussion, you can be concussed without losing consciousness. When concussion occurs in sport, players in most cases remain conscious, and the condition often goes undiagnosed. And while protective headgear prevents skull damage during high-impact knocks, it doesn’t prevent the brain from moving inside the skull.

People in certain sports have a higher risk of being concussed than the general population – rugby players and boxers, for example. People in the military who are exposed to explosions and victims of domestic abuse are also at particularly high risk. These groups are also more likely to suffer repeated concussions.

How is concussion medically defined?

Concussion is the mildest form of traumatic brain injury (TBI).

There is no universally accepted definition of concussion, but it results in:

  • Rapid impairment in brain function that is temporary and gets better by itself;
  • A variety of symptoms, but not necessarily loss of consciousness;
  • Disturbance to the brain’s function rather than physical structure, which means that standard neuroimaging tests such as MRIs and CT scans can’t detect any changes;
  • Symptoms that gradually improve over time, but which may be prolonged in a small percentage of people.

What are the signs or symptoms of concussion?

Two rugby league players are treated after clashing heads in a tackle.
Two rugby league players are treated after clashing heads in a tackle.
Mark Nolan / Getty
Many people who sustain a concussion have no observable signs, which can make diagnosis difficult. Recognising the condition often depends on the affected person reporting the symptoms they are experiencing. These can occur either immediately after the head injury or minutes to hours later.

People who have sustained a concussion may also report:

  • Confusion and inability to speak coherently;
  • Disorientation (for example, being unaware of time and place);
  • Lack of co-ordination (such as stumbling, or the inability to walk in a straight line);
  • Loss of memory (perhaps about the cause of the injury);
  • Slurred speech;
  • Delayed response to questions;
  • Appearing dazed or with a vacant stare;
  • Inappropriate emotion, such as crying for no reason;
  • Any temporary loss of consciousness

People who have sustained a concussion may also report the following symptoms:

  • Headache or a feeling of pressure in the head;
  • Confusion or difficulty concentrating;
  • Dizziness;
  • Changes in vision, or “seeing stars”;
  • Ringing in the ears;
  • Nausea and vomiting;
  • Fatigue;
  • Sensitivity to light;
  • Loss of smell or taste.

Recovering from concussion

In terms of short-term recovery, the brain changes that occur after a single concussion don’t appear to have clear long-term cognitive effects. Return to contact sport should be gradual: the ‘if in doubt, sit it out’ rule-of-thumb is now adhered to by many sporting codes.

A very small percentage of people who sustain a concussion go on to develop what is known as post-concussion syndrome. Symptoms usually develop seven to 10 days after a concussion, and can persist for weeks, months, and sometimes years. Why the syndrome occurs remains unclear.

The long-term consequences of concussion

While the short-term symptoms of concussion are reversible, research suggests that even a single knock to the head can have severe consequences later in life. For example, figures from one study that analysed the records of more than 160,000 trauma patients identified that, in patients aged 65 and older, just one concussion was associated with a 22-26% increase in dementia risk in the following five to seven years.

Even clearer is research showing that neurological damage accumulates with multiple knocks to the head, even when they are apparently symptomless, or ‘sub-concussive’. Repeated concussion has been linked to increased risk of neurodegenerative conditions such as Alzheimer’s and Parkinson’s disease, as well as chronic traumatic encephalopathy (CTE).

Data from studies of former American footballers is staggering. A survey of more than 2000 retired professional players found that those with a history of multiple concussions were three times more likely to have been diagnosed with clinical depression. Another study of death certificates found that the death rate from neurodegenerative diseases was three times higher for pro-footballers than the general population.

When should you seek medical advice?

Because the symptoms usually resolve by themselves, a concussion is best managed with physical and cognitive rest. However, stories about the potentially tragic consequences of undetected brain injuries are difficult to ignore. Symptoms of severe TBI can develop over several hours. Therefore, after a knock to the head, it’s important to be alert for the first 24 hours. Some symptoms are red flags for more severe brain injury: if a head injury results in a loss of consciousness, increasing confusion, vomiting or a worsening headache, the person should seek medical advice. It’s important that a doctor makes an assessment to rule out more severe TBI.


This story was prepared by the QUEENSLAND BRAIN INSTITUTE, and used with permission.

Read more about QBI’s concussion research here.

The Queensland Brain Institute (QBI), established in 2003, is a leading institute focussed on two of the greatest challenges of modern science: understanding brain function and the prevention and treatments of disorders of brain function.
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