Cosmos Q&A: Concussion

Concussion is sometimes still treated as a mystery in sport, but the field of concussion research began in 1928 – only six years after insulin was discovered. Nearly a century later there’s a lot we know, but an individual’s response to a concussion is highly specific and nuanced.  

However, given the airtime occupied by contact sports such as AFL, rugby and soccer, the concussion discussion has often been incorrectly seen as a problem mainly associated with sport. In reality, it can affect anyone who suffers an impact to the brain, such as a blow to the head or even from a sudden change of direction. So it’s really a public health problem.  

However, the statistics are still often skewed towards sports-related concussions, which only show a highly niche subset of the population – predominantly male sports professionals. Needless to say, most Australians aren’t part of this group.

“While the official rate of concussion, based on hospital admissions in Victoria only, is 18 per 100,000 participants, this data is terribly out of date (2011) and it is well known that the true figure is likely to be 6–10 times higher,” says Alan Pearce, a neuroscientist at La Trobe University.

This happens for many reasons. In the case of sportspeople it could be about fear of seeming weak or fear of missing a selection round; in the case of the general public, it’s often about just not being aware of the prevalence and symptoms of concussion.

This means that concussions often go unrecognised by the people who suffer them, purely because so much of what we know and hear is geared towards professional sport. People who suffer falls, impacts with a wall, or who play amateur sport are also less likely to have access to immediate medical attention, and are often slower to receive a diagnosis.

This also means that diagnoses and treatments can differ, as many are geared towards “return to play”, which is based on whether symptoms are present or not. This is not a good indicator of concussion in the first place, as it’s subjective; firstly because concussion symptoms are so individual, and also because they’re not always based on objective data.

Current diagnoses on the field rely on subjective markers that can lead to both false positives or false negatives. Off the field, the ‘gold standard’ of concussion diagnosis is using blood mRNA, which are small RNAs expressed due to trauma. 

“When an individual is concussed, there are a release of molecules and neurotransmitters into the extracellular fluids which not only include blood but also saliva, lymph and other tissues that with the right test can pick up these markers,” says Pearce. “The issue has been [finding] which markers represent potential microdamage to brain tissue causing impairments.”

This is not to say that diagnostic practises are bad, just that they could be bolstered with other objective data, too. Ultimately, return to play and recovery can be two separate things.

Ultimately what this means is that concussion manifestation and recovery is a question of science, not sport.

We asked Pearce some of the key questions about concussion(s) to get a better understanding. 

What happens inside the skull to cause a concussion?

Concussion is first and foremost a brain injury. But the signs and symptoms of concussion, which are the mildest on the brain injury ‘spectrum’ (from mild to severe) represent a transient disruption in neurological function following an impact to the brain (or an indirect impact to the body that transmits the force to the brain).

While the brain doesn’t change shape per se; the disruption in function is due to the impact stretching and shearing the neurons. The damaged neurons will release molecules and neurotransmitters into the extracellular space which makes neural transmission (ie impulses) impaired. This is why you see the signs and symptoms common to concussion. 

What type of matter is the brain and how does that affect internal injuries compared to other organs?

Brain tissue is very delicate. Unlike a ‘fixed’ brain – the ones we used to dissect in biology classes – the consistency of brain tissue is little more than “chunky custard”. If you were to take your brain out of your skull, you could squeeze the contents through your fingers with a little bit of force. What protects our brain tissue is our skulls, which can take a certain amount of force, as well as the brain sitting in a little bit of fluid, called the cerebrospinal fluid, which acts as a shock absorber – to a point.

At higher impacts, the cerebrospinal fluid acts against the best interests of the brain by allowing for greater movement of the brain tissue in the skull. Combined with the delicate nature of brain tissue, this can lead to greater injury than other organs that are more robust in their micro-anatomy.

The egg yolk analogy is a good one, but just imagine the egg yolk having an outer layer, and an inner layer that then creates two different speeds of movement – this is how the stretching and shearing effect occurs.

How quickly does the brain chemically react to a concussion?

Pretty much immediately.

One thing that confuses people is the notion, which is frequently referenced in sport, of “delayed concussion”. 

The “delay” is only in the symptom reporting. Following the impact, the chain of events is already in place and it may not be until a certain threshold of impairment that the individual expresses some symptoms, either through self-reporting, or via their behaviour. 

Symptoms are not a good indicator of concussion.

Do concussions affect any other parts of the body/health beyond the brain? 

Given that concussions/mild brain injuries affect the central nervous system, the knock-on effects are usually to the peripheral nervous system that controls muscle contractions. This can affect balance and coordination at the time, and also during recovery periods. 

Concussions also affect the autonomic nervous system, so they can influence such things as heart rate variability and sleep patterns.

Do genetics, biological sex or background influence how a concussion can affect a person?

These are some of the big questions we are trying to investigate at present. We know that if a person has had a previous concussion(s), then subsequent impacts to the head do not need as much force, and the individual will usually express more severe symptoms and will take longer to recover.

This is one reason why I have been campaigning hard publicly for longer recovery time when an athlete is concussed.

With the caveat that the research is very limited at present, we know through the emerging evidence, that women tend to report more severe symptoms and take longer to recover following a concussion compared to males. However…in saying that, while there appears to be some physiological mechanisms for this, I don’t think that it’s as disparate as it’s being made out to be. 

One reason is that majority of research is currently still relying mostly on symptom self-reporting, which I think is a terrible indicator, and in 2017 I published this research which showed differences in attitudes and behaviours towards concussion reporting between females and males. 

Essentially, due to cultural reasons, males are less likely to be honest in their reporting of concussion and say that they are ready to get back to play much sooner than females!

Genetics is still a very big unknown at present. While we have the APOe gene linked to boxing, where impacts to the head are very frequent and expected, it doesn’t appear to be as strong in contact sports where impacts to the head are more incidental. 

Does a child’s brain behave differently to an adult’s brain when it gets a knock on the head/as it recovers from a concussion?

We know it takes much longer for a child’s/adolescent’s brain to recover from a concussion than an adult brain. Moreover, the concern is on the long-term effect of trauma to the developing brain. That’s one reason why children/adolescents need almost double the time for rest and recovery following a concussion than adults, and that the consensus is a return to school should occur before a return to sport.  

Is there a point where the brain can no longer fully recover? Why?

That’s a tough question to answer. Because some people after one concussion never recover. I have people coming in to my lab who have had ongoing symptoms more than a year, and some have them for as long as 5 or 6 years and they’re still struggling.

With my retired players study, the number of concussions after which the player has chronic issues sometimes may be only a couple, where others report 20. But the common thing here is their career in the sport (several decades), during which their brains have been subjected to repeated trauma without concussions (sub-concussive impacts).

What is the scientific justification behind the 11/12 day rules? Is this based on a statistic? 

Another good question. We don’t actually know as they have not provided any specific evidence for this change. 

You may want to see my recent paper, currently under review in Sports Medicine journal, where I looked at four years of concussion and return-to- play data showing that in 2020, return-to-play times for AFL players reduced by nearly half that of 2019. 

The issue of COVID and the modified fixtures in 2020 should actually have helped increase the return-to-play times, but in fact it did the opposite. The interesting number is that it seems to match closely to the 12 day rules that AFL brought in this year.

The AFL announced in January that it was doubling mandatory time out of the game for players who suffer a concussion, with at least 12 days needed before they can take the field again.

The AFL said the 12-day return-to-play protocol “is an increase on the previous six days required under the 2020 guidelines as the AFL adds further protection for players.

“Under the new rule, all AFL and AFLW players who suffer a concussion will miss at least one match under standard fixturing due to the mandated time off.”