If you suffer physical injuries in a road accident, you could sue the other party for damages and you would probably win if you were in the right.

But it would be much harder in Singapore to try to get compensation for any emotional injury you might claim to have also suffered in the accident.

Still, in December 2013, a victim of a drunk hit-and-run driver won about $60,000 in compensation for a type of mental pain and psychic suffering she sustained after physical trauma. Her condition is called post-traumatic stress disorder (PTSD).

Physically, the woman suffered only bruises in the accident. But later on, she was diagnosed with PTSD when she reported persistent nightmares and flashbacks of the accident.

Reports suggest that hers may well have been the first case in Singapore where a victim was compensated for PTSD.

Most people who experience or witness a traumatic or terrifying event may become distressed for a period but do eventually get over it. However, if they continue to re-experience the trauma in nightmares, intrusive memories and flashbacks for more than a month and to such an extent that they cannot function normally, they may be said to have developed PTSD.

The condition may set in after exposure to serious physical injury, actual or threatened death, or sexual violence, especially in rape and child molestation cases.

To be sure, such emotional suffering can be feigned and its diagnosis would depend to a large extent on the patient's self-reporting in the psychiatric clinic, which translates into merely subjective testimony in court.

When someone deliberately feigns or exaggerates such symptoms, usually for possible financial gains, it is called malingering, which is common in alleged PTSD cases.

Unfortunately, there is no foolproof way to expose malingering. But it also means that if you are suing for PTSD, it will be a huge challenge to prove your purely emotional harm, an invisible injury.

Physical injuries can be easily verified by doctors, but it is hard to convince the court that you have suffered PTSD. Since it is difficult to verify, you may be denied compensation.

Victims seeking compensation for emotional injuries make up just one side of the coin. The obverse comprises those convicted of a crime who may seek a lenient sentence by claiming PTSD as a mitigating factor - saying, for example, that they suffered a flashback while committing a crime.

So there are two situations: One where litigants may fake PTSD symptoms to win more compensation while the other involves convicted persons claiming PTSD to avoid a harsh sentence.

Indeed, sceptics would argue that anyone who has had a horrific experience of abusive violence would suffer some level of distress but that cannot be construed to be a psychiatric disorder. They would argue that, when a patient himself reports the trigger event of trauma and claims that his PTSD symptoms persisted afterwards, it cannot be relied upon in a court of law.

The earliest acknowledgment of PTSD came after World War I when soldiers were frequently diagnosed with "cowardice" when they were, in fact, shell-shocked. PTSD has sincebecome a powerful term in Western cultures, not infrequently raising its head in high-profile criminal court cases.

There was little PTSD research until the tail end of the Vietnam War, when a scientific consensus emerged that "terror and fright" in the context of an intensely traumatic experience can cause injuries to the brain.

While ordinary people and the courts may remain sceptical about such injuries, psychiatrists have been persuaded that there is truth in these claims by victims. PTSD became a formal diagnosis in mainstream psychiatry in 1980.

Today, expert estimates put its prevalence at 10 to 15 per cent of individuals exposed to trauma - with higher rates in victims of sexual violence than even those with experience of combat trauma.

Recent technology offers to shed some light on the biological basis of the harm that PTSD patients sustain from exposure to extreme stress. It is possible to do a visual measurement of the activity in a PTSD brain as it processes pain.

While older technologies like X-rays or CT scans reveal the physical structure of the brain - not its activity - newer technologies especially fMRI (functional magnetic resonance imaging) can non-invasively measure living brain activity while a person answers questions or experiences a painful test stimulus.

If you have a chronic headache, say, the doctor may order a standard MRI. This provides images of the brain structure and can show up any structural problems such as tumour, stroke and so on. But it does not tell how the brain is working.

This is where the fMRI comes in. The person undergoing an fMRI is asked to think about, look at or listen to something - tasks causing increased activity in the brain region of interest - while the scanner looks for changes in the flow of blood with a lot of or little oxygen to those specific regions. It is assumed that the brain areas where neurons have just fired off will receive an inflow of oxygen-rich blood just a few seconds afterwards.

Sophisticated statistical software is used to analyse the data to transform it into videos of the functioning brain.

Since 2007, there has been increased funding for PTSD research in the United States because of affected soldiers returning from Iraq and Afghanistan.

This research is showing that specific nerve circuits in the brain are dedicated to emotional function. It is also showing that, in most people, new brain cells develop that connect up with one another to help overcome traumatic memories.

But in some individuals, the deluge of stress hormones released in a traumatic experience is enough to cause cellular damage to the brain. In such individuals, new brain cells and their interconnections fail to develop in specific brain regions (especially the amygdala, pre-frontal cortex and hippocampus), which also tend to be measurably smaller in PTSD brains than normal brains.

What the research indicates is that some people may be born with brains that are more prone to PTSD. The result is that the fear response that most people have fails to turn off in such individuals, who then go on to develop PTSD.

So PTSD may be seen as a physical disorder with mental effects. What this suggests is that "mental" and "physical" may not even be separate categories. Instead, many scientists now see emotions not so much as subjective feelings but more as something with a cellular or bio-physical basis in the brain itself.

The courts, however, will likely continue to maintain the distinction, if only to avoid opening the floodgates to claims for compensation for emotional injury.

Only when scientists can make a specific diagnosis of PTSD with fMRI scans and biomarkers, which is possible in the medium term, might the courts change tack.

•This is the fourth of a six-part series by Andy Ho on new scientific findings about the brain.

NEXT WEEK: The forgetful brain