Save our brains: how dangerous is sport?

You're listening to The Conversation. Where I live in Melbourne, Australia, this is the sound of our weekends.

This is Australian rules football, and kids play it from when they're six or seven years of age.

But a few weeks ago, it took a tragic turn. A much-loved Melbourne football player remains on life support this morning after a heartbreaking injury during a match.

The 27-year-old was playing for Epping's reserves team in Leylaw on Saturday.

He has died in hospital after suffering catastrophic injuries in a free clash during a game in Melbourne's north.

Nathan Fitzgerald copped three hits to the head during a tackle. He was only 27 years old when he died.

It's prompted a reckoning about the sport we treat like a religion here. Is it safe? Should our kids play?

And what kind of duty of care do we owe the players who take to the field every weekend?

I'm Neil Seawang, Sports Editor at The Conversation, a news and analysis platform partnering journalists with academics.

Welcome to The Conversation Weekly, where experts explain how we ended up here.

Alan Pearce, as a neuroscientist, you've been researching sports-related concussion for more than two decades.

When you first started working in this space, how much do we know about the risks of head knocks and concussion and CTE?

We have known about concussion in particular for quite some time.

So concussion is a single traumatic brain injury.

So, you know, I get on my high horse here and I sort of hate the term head knock because it's more than a head knock. It's a brain injury.

And you see the signs and symptoms straight away after a concussion.

There was a fair amount of research around

concussion in particular, but

not necessarily from a longitudinal aspect in terms of players later in life and retirement, and certainly not around chronic traumatic encephalopathy or CTE.

Footy legend Polly Farmer has become the game's first player to be posthumously diagnosed with the crippling brain disease known as CTE.

The first case of a degenerative brain disease linked to constant head knocks in a New Zealand professional rugby player has been confirmed.

So there's been a lot of work in

the last sort of 10 years now and that is because

we do have good evidence coming through

from the brain banks around the world showing I guess pathology evidence you know good strong evidence that

CTE is a real disease and it's also relating to repetitive head impacts rather than concussions per se.

So there has been quite a bit happening but we've still got a long way to go here.

So what exactly is CTE and what do we know and not know about its causes?

CTE is what we call a neurodegenerative brain disease, not unlike other dementias but it

certainly has very specific characteristics that differentiate it from other dementias like Alzheimer's or vascular dementia or frontotemporal dementia.

And if we compare it to Alzheimer's, for example, where it starts in the deeper part of the brain, CT is very specific around the outer part of the brain.

And where it first starts is at what we call the valley.

So you have the lumpy, bumpy look of the brain, and it's sort of filled with hills and valleys.

And at the very bottom of those valleys is where we start to see the early stages of CTE.

And that is because what we see is a, I guess, a relationship to physical trauma.

And so unlike other dementias or even diseases like motor neuron disease, where it can start spontaneously, it's age-related,

it's family-related as well, CTE is really very much starting because of physical trauma, and it's not just in old people.

We see this in young people as well. So that's probably the biggest difference.

So we find that players, athletes, military, unfortunately domestic violence,

where the person has never been concussed but has received hundreds and thousands, and in some cases tens of thousands of repeated impacts diagnosed with CTE.

And then on the flip side, you have people who have had 50 concussions in their career aren't diagnosed with CTE.

So it's one of those things that we're still finding out, but the evidence is pointing towards repetitive head impacts.

We've seen a slew of former AFL and rugby players come out recently about their experiences with brain injuries?

From the age of probably 42 I'm starting to deal with memory loss and stuff.

When it impacts you through everything you know your ability to work, your ability to sleep, you know got headaches every day.