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By the end of World War One the army had identified 80,000 cases of a new condition they termed as 'shell shock'. 

Scientists have been perplexed by the symptoms - that include anxiety, facial tics as well as terrible nightmares - ever since but, after more than a century of research, the mystery may have been solved.

Experts now believe that a honeycomb pattern of broken nerve fibres in the brains of veterans that survived improvised explosive devices (IED) attacks, is responsible for the condition officially termed as blast neurotrauma.

By the end of World War One, the army had identified 80,000 soldiers suffering from shell shock and after 100 years, scientists have now discovered a honeycomb pattern of broken nerve fibres in the brains of veterans that seem to show the brain injury caused by war. British soldiers in the trenches are pictured

Researchers at Johns Hopkins University School of Medicine in Baltimore, Maryland, conducted autopsies on US combat veterans who survived blasts in Afghanistan and Iraq, but later died of other causes.

They discovered that they had the same kind of brain injury – a distinctive honeycomb pattern of broken and swollen nerve fibres throughout critical brain regions, including those that control decision making, memory and reasoning.

The pattern is different from brain damage caused by car crashes, drug overdoses or collision sports.

Vassilis Koliatsos, a professor of pathology, neurology, and psychiatry and behavioural sciences at the university, explained that survivable blasts may cause hidden brain injuries that play a role in the psychological and social problems some veterans face after coming home.

The scientists explained  that survivable blasts may cause hidden brain injuries that play a role in the psychological and social problems some veterans face after coming home. Here, a soldier breaks down in Iraq after learning his friend was killed, and another (centre) suffers from burns caused by a blast

'This is the first time the tools of modern pathology have been used to look at a 100-year-old problem: the lingering effect of blasts on the brain,' he said.

Molecular probes were used to reveal details in the brains that they examined, according to the study, published in Acta Neuropathologica Communications.

Senior author, Professor Koliatsos, said: 'We identified a pattern of tiny wounds, or lesions, that we think may be the signature of blast injury.'

'The location and extent of these lesions may help explain why some veterans who survive IED attacks have problems putting their lives back together.'

Soldiers have struggled with bomb-induced brain damage, which was dubbed shell shock, since 1914, when German and Allied forces bombarded each other for months on end.

The condition is now known as blast neurotrauma and still  affects some soldiers who served in Iraq and Afghanistan, where the use of IEDs were widespread.

Doctors treating IED survivors 'often see depression, anxiety, post-traumatic stress, and substance abuse or adjustment disorders,' said Professor Koliatsos

'Life is very difficult for some of these veterans and it's important to understand that at least a portion of these difficulties may have a neurological foundation.'

In the study, the scientists used a molecular marker to track a protein called APP that normally travels from one nerve cell to another via a long nerve fibre, or axon.

When axons are broken by an injury, APP and other proteins accumulate at the breaks, causing swelling.

The study revealed that bulbs on the nerve fibres of the soldiers were medium-sized, unlike those of people who died in car crashes or drug overdoes. Near the damaged axons, specialised cells, called microglia, that are involved in brain inflammation, were revealed. A stock image of a mammal microglia cell is shown

Shell shock, now known as blast neurotrauma, affects many soldiers who served in Iraq and Afghanistan, where the use of IEDs were widespread. War poets Siegfried Sassoon (left) and Wilfred Owen (right) both suffered from the condition, which Owen described as 'minds the Dead have ravished'

In the brains of people killed in car accidents, the swellings were large and bulb-shaped, while in cases of methadone overdose, these axonal swellings were small.

In the brains of four of the five veterans who survived wartime blast injuries, the axonal bulbs were medium-sized and usually arrayed in a honeycomb pattern near blood vessels.

'We did not see that pattern in other types of brain injury,' Professor Koliatsos said.

The veterans' brains did not show signs of the neurodegenerative disease known as punch-drunk syndrome, which is caused by multiple concussions.

But near the damaged axons, specialised cells, called microglia, that are involved in brain inflammation, were revealed.

Dr Koliatsos explained: 'In brains that had been exposed to blasts, we see microglial cells right next to these unusual axonal abnormalities.

The presence of these cells suggests the veterans who overdosed had pre-existing brain injuries.

Lesions may be fragments of nerve fibres that broke at the time of the blast and slowly deteriorated, or may have been weakened by the blast and broken by some later accident like a concussion or drug overdose, the study says.

Soldiers have struggled with bomb-induced brain damage, which was dubbed shell shock, since 1914, when German and Allied forces bombarded each other for months on end, here a soldier writes a letter home