By: June Cheong

Humans face moral dilemmas, from fleeting everyday decisions to life-or-death questions.

Should I give up my seat on the train for a frail, elderly person? Do I snatch a cab from another who has been waiting longer just because I have a pressing matter to attend to?

Should I have an affair?

If there are two similar, competing organ recipients, which one deserves that second shot at life more?

Morality is a murky soup of nature versus nurture, it seems.

Some scientists believe that our moral compass is hardwired into our brains while others believe that our surroundings and people close to us help shape our thoughts and actions.

While the experts have their disagreements on this subject, they concur on this: The tussle between doing good or evil resides in the brain.

Dr Melanie Storry Chan, a consultant psychologist at The Counselling Place, said: 'Moral decisions reside in the ventromedial prefrontal cortex (VMFC).

'This area of the brain is responsible for highly complex functioning such as empathy and the ability to make moral judgments.'

The VMFC in an adult is the size of a large plum and is found about 5cm behind a person's forehead.

The case of Phineas Gage, a railway construction foreman in Vermont in the United States, famously illustrates how the VMFC affects one's moral bearings.

In an accident on Sept 13, 1848, a steel rod entered the 25-year-old's left cheek bone and exited through the top of his head.

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Although he later recovered, his personality was forever altered as most of the frontal cortex of his brain was destroyed.

Dr Storry Chan said: 'Before the brain injury, Gage was considered a good worker, popular and efficient.

'But after that, he was angry, used the grossest profanities, became impatient and was 'no longer Gage'.'

Indeed, a 2007 American study of patients with ventromedial injuries and those without such injuries found that the VMFC is key to making a moral call.

Dr James Khoo, a consultant neurosurgeon at Neurological Surgery, gave the example of a brain that is damaged by dementia.

'I see a change in people who develop dementia. They swear more, may steal things or do things they previously knew were bad,' he said.

The ventromedial area is connected to other regions like the brain stem, responsible for bodily functions like breathing and heart rate; and the amygdala, important for perceiving and reacting to emotional or affective behaviour and feelings like fear and anger.

It thus acts as a central system, collating information from these various brain regions to come up with an appropriate social response. Damage to this area disrupts or severs this vital function.

Another major area also comes into play in moral decisions - the dorsolateral prefrontal cortex which approaches situations in a strictly cost-benefit analysis way.

A study last year by the University of Illinois, Champaign-Urbana and the California Institute of Technology found that our moral decisions are also affected by how much weight our brain places on fairness.

Just last month, a study published in the scientific journal PNAS found that individuals who behave dishonestly exhibit increased activity in parts of the prefrontal cortex, whether they chose to behave dishonestly or not.