Two 11-year-old Cuban boys face each other in the ring during a boxing training session at an Old Havana neighborhood boxing gym, in this Aug 12, 2003 photo. When it comes to boxing, health experts and scientists - and even some competitors - have been worried about brain injuries for decades. Irish former featherweight world champion Barry McGuigan said in 1988: "Boxing damages your brain; don't let anyone tell you any different." [Photo/Agencies]

Top: The NFL helmet's health-warning sticker is pictured between a US flag and the No 55, in memory of former student and NFL player Junior Seau, as the Oceanside Pirates high school team prepared for a Friday game in Oceanside, Calif, last September. Above: New England Patriots linebacker Seau celebrates in this Oct 7, 2007 file photograph. Advances in modern neuroscience mean scientists know more than ever about chronic brain damage and the long-term trauma that can result from frequent knocks to the head. [Photo/Agencies]

Evidence is rapidly mounting that contact sports cause brain injuries, Reuters reports.

When Ireland's Katie Taylor was taking hits and striking blows for boxing's Olympic debut in an east London ring last year, John Hardy did not want to look. To this leading neuroscientist and molecular biologist, a boxing bout is little more than a session of mutual brain injuries. He was horrified to see women boxing at the Olympic level for the first time at the London 2012 Games.

"We shouldn't get our fun out of watching people inflict brain damage on each other," said Hardy, who is chair of Molecular Biology of Neurological Disease at University College London's Institute of Neurology. "To me as a neuroscientist it's almost surreal."

Hardy, whose research work focuses on Alzheimer's and other types of dementia, said having women in an Olympic boxing ring was "a terrible thing" - not because he thinks women should not compete alongside men in sports, but because women boxing simply meant more people inflicting more damage on more brains.

That, in turn, was highly likely to mean more people suffering the devastating, incurable symptoms of brain diseases such as Alzheimer's.

Advances in modern neuroscience mean scientists know more than ever about chronic brain damage and the long-term trauma that can result from frequent knocks to the head.

"You get tiny lesions along the blood vessels where they have torn the nerve cells around them. This damages those nerve cells, and those cells start to develop the tangles that you see in Alzheimer's disease," Hardy said.

"And what we now understand is that this process spreads."

Partly due to this new understanding, now is a time of intense sensitivity about and scrutiny of brain damage in sport - particularly among North America's NFL players.

Former San Diego Chargers player Junior Seau committed suicide last year after what some believe were years of depression stemming from multiple concussions he suffered as a player.

Last week, the NFL and General Electric Co announced a $60 million effort with leading neurologists to speed up research on brain injury to improve diagnosis and treatment amid growing concern about sports-related concussions.

Rule changes

A study published last year found that even minor repeated head blows during sports such as hockey and football may damage the learning ability of sports men and women after just one season.

The brain debate has even reached the White House, where President Barack Obama suggested in January that changes be made to NFL rules to reduce the level of violent impact.

In soccer too, concerns are growing about the damage players might be doing to their brains when they head the ball.

A small study of female soccer players published last month found evidence of mental impairment caused by repeatedly bouncing a soccer ball off the head. The US researchers who conducted that study said the effects suggested headers caused "mild traumatic brain injury of the frontal lobes".

When it comes to boxing, health experts and scientists - and even some competitors themselves - have been worried about brain injuries for decades.

Irish former featherweight world champion Barry McGuigan, perhaps fearful of what damage might already have been done, said in 1988: "Boxing damages your brain; don't let anyone tell you any different."

Around the same time, fellow lightweight fighter Terry Marsh, who was later diagnozed with epilepsy, said: "I don't need the British Medical Association to tell me getting hit on the head can't do me any good."

As far back as 1928, the American pathologist Harrison Stanford Martland wrote a paper entitled "Punch drunk" in which he showed that prize fighters were suffering from brain injury caused by the rupture of blood vessels.

The "punch drunk" condition, known more formally as chronic traumatic encephalopathy or as its variants, dementia pugilistica or boxer's dementia, is a neurodegenerative disease that can affect boxers and others who suffer knocks to the head.

It can cause depression, aggression, impulsivity and memory loss and has been linked to suicide.

"A lot of boxers, and indeed American footballers too, have a period in their 30s and 40s where they are depressed, they drink, they show explosive tempers, and have basically pretty messed up lives," said Hardy.

Bad judgement

It is not hard to find examples of boxers whose brains have begun to fail them.

American heavyweight champion and boxing idol Muhammad Ali began struggling with a stutter and trembling hands even before he came to the end of his fighting career. His subsequent decline with the neurodegenerative disorder Parkinson's syndrome has been painful for fans to witness.

Mike Tyson, a former undisputed heavyweight champion of the world, was convicted and imprisoned for rape, had multiple marriages and break ups, was declared bankrupt and was eventually diagnosed with the brain condition bipolar disorder.

British former heavyweight world champion Frank Bruno was diagnosed with the same condition, while his compatriot Michael Watson needed six brain operations and suffered lasting damage after being knocked down in a 1991 bout.

Hardy argues there is a tendency to think of these problematic lives as par for the course for boxers - who were more likely than non-boxers to come from disadvantaged backgrounds and mix in unstable circles.

"But the truth is they have bad judgement because of the injuries to their brain," he said.

In the language of brain science, this was called "loss of executive control", he explained, "and this in itself is part of the disease process".

"It's not inherent in their personalities as boxers, it's damage to the frontal cortex. They are already experiencing brain injury."

In an article posted on the World Boxing Association's website, Calvin Inalsingh, head of the association's medical advisory committee, admits "boxing is the only sport in which the objective is to render blows to the head and body of the opponent so as to cause the opponent to be incapacitated".

It is this, according to Hardy, that means when it comes to arguing for a ban on sports that cause brain injury, boxing is in a class of its own.