New light on 'fight or flight'

PUBLISHED : Sunday, 03 July, 2011, 12:00am
UPDATED : Sunday, 03 July, 2011, 12:00am


For thousands of years, ever since humans first came down from the trees - only to meet greater dangers - we have developed biological mechanisms to protect us. The visual receptors in our eyes can react to stimuli - such as fast-moving leopards and cars - in tenths of milliseconds. We are built to react quickly and efficiently.

While studying how the eye reacts to light, researchers at the University of Science and Technology have stumbled upon a new mechanism that is likely to trigger renewed interest in the so-called 'fight or flight' response.

Zhang Mingjie, chair professor of life sciences, and his team have identified a protein in the visual systems of animals and insects which could help to explain survival responses.

The INAD protein operates like a switch that regulates the reception of the brightness and dimness of light by modulating the sensitivity of photoreceptors in the eye. It is the rapidity of its modulation, says Zhang, that enables a person to visually process an oncoming train, or allows a fly to escape a fly swatter, under different conditions of light.

But this biochemical mechanism, important as it is, is only a part of our larger 'fight or flight' system. For humans, our protective mechanisms were in place long before our higher cognitive functions - those which made us Homo sapiens, the 'wise man' with a highly developed brain - took hold.

Our immediate reactions to danger are triggered by the oldest part of our brain: the area closest to the brain stem, the hypothalamus and its neighbour, the pituitary gland. Together with the adrenal glands, the three form the so-called hypothalamic-pituitary-adrenal axis (HPA axis), which controls reactions to stress as well as regulating other bodily processes.

Whenever the body meets a perceived threat, uncontrollable physiological changes spurred by the HPA axis occur. Our muscles tighten, readying us to run. Our breathing gets faster and our blood sugar rises. Our heart pumps more - and at the same time, blood flow is diverted from less immediately necessary functions like digestion.

Since 1915, scientists have been calling this response 'fight or flight'. The term, coined by Walter Cannon to describe animal responses, is a handy moniker for the slew of physical effects that prime us for survival. It made ancient man ready to deal with the threat of sabre-toothed tigers or other predators.

But though we are seldom confronted by tigers nowadays, our bodies still produce survival responses to stimuli.

So what happens in a world where most of us no longer have the option either to fight or to run? When we are in a stressful situation in the office and can neither punch our boss nor run away from our cubicles?

Some research points to the toxic effects of accumulated stress chemicals on the immune system.

In a study at Carnegie Mellon University, people with higher levels of corticotrophin-releasing factor (CRF) in their bodies - a chemical sign of higher stress - were found to catch a cold more easily. And in the long-term, the stress chemical cortisol may also destroy brain cells associated with memory.

Physiologically, the human body still responds to stress in much the same way it always has done. But humans have learned to cope with in new ways, and this in turn affects our physiology.

Our higher cognitive functions -such as analytical thinking - controlled by the more evolutionarily advanced cortical regions higher up in our brain (closer to our forehead) allow us to assess danger without necessarily succumbing to automatic reactions.

The difference between humans and animals is that humans have larger cortical regions. It means we can process more things, says Agnes Chan, a professor of psychology at the Chinese University of Hong Kong. 'Animals respond to stress very instinctively. For human beings, when we see something which arouses stressful feelings, we analyse it... We think of many, many alternatives, which animals will not do.'

Dr Xiao Lu Wang, a researcher at the Centre for Behavioural Health at Hong Kong University, agrees, but with a caveat. 'Instead of the quick fight or flight response, you gain more resources by saying: 'Okay, let me step back for a moment,'' she says. But a problem with this is that while animals can immediately forget about what stressed them after it's gone humans, with their larger cortical areas, can remember the stress, creating a more constant plague.

'Some people will respond to stress by relaxation,' says Chan. 'If I stress and learn something to relax myself, then I will feel much better. But the bird won't learn relaxation, or the lion or tiger.'

We can also take our aggression out on the treadmill instead of another being. Or we can turn to others for support.

Zhansheng Chen, who studies social rejection and hurt at Hong Kong University, says that some people can respond very aggressively when they feel they're being mistreated (fight), while others can withdraw (flight). But sometimes, he says, people will cope in other ways. People who are not liked by others will sometimes 'try to be nicer, behave more properly so others will accept them,' he says.

In a landmark study in 2000, scientists found that most studies on 'fight or flight' in the past had been performed on male participants. With females, however, they found another reaction to stress. They called it 'tend or befriend'. From ancient times, pregnant women could neither flee nor fight, so it was safer if they formed group bonds, two scientists from UCLA, Shelley Taylor and Laura Klein, found.

And such behaviours are not limited to women: men, too, can choose options other than fight or flight.

Professor Daniel Levine at the University of Texas-Arlington studies what makes us choose to cooperate rather than compete.

'As we evolved from other animals to humans, we developed a larger frontal cortex and we've got all these different executive areas and we can control our responses,' he said. 'The further up we go in evolution, the more control we have over our responses so it's not like the fight or flight isn't still there. It came as a result of evolution, we inherited it from other animals, but we can control it. It's not completely automatic.'

Stress-relievers - relaxation, exercise, supportive environments - are all options we can choose with the frontal parts of our brain, overriding our automatic stress responses, even as modern-day sabre-tooth tigers in the form of dead-lines and social rejections roam our way.

'An individual is not destined to act a certain way just because of our genes,' Levine said. 'We need to defend ourselves but we also need to cooperate, so these are two different evolutionary programmes sometimes in conflict. Sometimes we treat the person next door as if they were the sabre-tooth tiger and that doesn't make sense.'