Does stress help us succeed?

Don't worry – and it might happen. Worrying may be a key to survival; a first step in the body's defence strategy when faced with threats. Pioneering research using brain scanners has located the worry centre of the brain and suggests for the first time that it is an area involved in survival and the assessment of threats and risks.

The same team of researchers has also shown that drugs used to treat worry or anxiety disorder have an effect on humans' defensive reactions.

"Feelings like worry and anxiety may be unpleasant, but it seems they are part of our defensive repertoire and help keep us safe and it is only when they become exaggerated do they represent an illness," says Dr Adam Perkins of King's College London. "Our ultimate aim is to improve the detection, diagnosis and treatment of illnesses, such as anxiety, where there are unusually strong and debilitating forms of worry."

Fear has been linked to the "flight or fight" response, which prepares the body to confront the threat or run away, by triggering physiological changes including a tensing of muscles ready for action and a faster heartbeat to get more blood flowing.

It's now suggested worry may have evolved as an earlier reaction, as a way of assessing potential threats before fear kicks in.

Worry or anxiety has been defined as an unpleasant emotional state involving apprehension, dread, distress, and uneasiness. Fear is similar, but involves a specific object. In the new research , scientists set out to find out what happens in the human brain when we worry. No similar research has been carried out on humans.

Dr Perkins and his team developed a video game designed to produce similar anxiety effects in humans as those induced in animals. It is a computerised human version of a task used to measure defensive reactions in rodents. The 12 men and women each played the game while inside an MRI scanner. Scientists used functional magnetic resonance imaging (fMRI) to track activity in the brain when the men and women were completing the computer game.

When areas of the brain increase their activity, the amount of oxygen that they use increases and that can be detected with fMRI.

The main theory the scientists set out to test was that the hippocampus would become highly active when people were in the phase of the computer game when they were anxious or worrying. This area of the brain was previously thought to be associated primarily with long-term memory and spatial awareness. Initial results support the hypothesis and bigger studies are now planned. The hippocampus also plays a role in the fight-or-flight response by triggering physiological changes including a tensing of muscles ready for action and a faster heartbeat to get more blood flowing to the brain and muscles.

Nerve cells pass the perception of a threat to the hypothalamus, which sends signals down the spinal cord to the adrenal glands and chemical messengers are released which results in the stress hormone, cortisol. It in turn orchestrates a cascade of physiological responses which result in an increase in blood pressure and sugar levels and a suppression of the immune system. Cortisol sets fatty acids free to be transformed into energy for muscles: ready for action. Anxiety and excessive worry were once thought to be wholly learned, but we are now realising they may be caused by alterations in the functioning of brain systems that evolved to control defensive reactions,'' says Dr Perkins.

"We have shown that the hippocampus is involved and that suggests that worry is part of the human defensive response. We knew fear was part of that repertoire, which is linked to flight-or-fight reactions, but it now seems worry is, too, with the hippocampus as the worry control centre in the brain, which is activated when we are in a situation of potential threat."

As well as providing new insight into the functioning of worrying and anxiety, the findings of the research, part-funded by AXA, may lead to new treatments which target the hippocampus. Professor Stephen Williams, head of neuroimaging at the Institute of Psychiatry, at King's College, where the work was carried out, said: "This study investigates for the first time the role of the human hippocampus in a realistic risk assessment situation using functional magnetic resonance imaging.

"These are very exciting results and could lead to the development of new therapies in the treatment of anxiety disorders focusing on the hippocampus." Worry, which has long been a source of fascination, intrigue, and challenge for poets, philosophers and psychiatrists alike, is universal, but research is increasingly showing wide individual variations.

Most people are in the middle of the "worry continuum". They fret about money, children and everyday things, but it doesn't interfere with their daily lives. In fact, mild-to-moderate anxiety has been shown to have tangible benefits. A study of patients having minor surgery showed that those with moderate anxiety did better post-operatively than those with high or low anxiety levels. One theory is that moderate anxiety about real threats helps people cope with those challenges. There are those who worry all the time and for whom anxiety is a disabling, excessive, irrational dread of everyday situations.

One in 10 people is estimated to suffer at some time from one or more of the big five anxiety disorders – generalised anxiety disorder, obsessive-compulsive disorder, panic disorder, social phobia and post-traumatic stress disorder.

It also emerged that there are people who worry less than normal. People with ADHD, for example, may have lower levels of anxiety and so too may psychopaths. Low levels are also found in risk-takers.

"Worrying is important, but it should not be seen in isolation,'' says Dr Perkins.

"Anxiety doesn't bring happiness, but it can bring success, especially when combined with intelligence.

"Biographical information about Charles Darwin, for example, suggests he was plagued for much of his adult life with severe anxiety, but he was also substantially more intelligent than the average person.

"As a result, although he appears to have felt miserable much of the time, his superior intellectual ability meant his anxiety was channelled into the highly-important work of worrying about the origin of species rather than some trifling matter, such as whether or not his socks matched his trousers. Someone with the same levels of anxiety as Darwin, but half his IQ, might well have ended up roaming the streets and eating from bins.

"People who worry and are also blessed with high IQ tend to be visionaries, planners, creators and inventors. People who do not worry much at all, but are also highly intelligent, tend to be the successful implementers in frontline, stressful situations. For example, fighter pilots typically have low levels of trait anxiety and are able to operate their planes on highly-dangerous combat missions, the mere thought of which would give an anxiety-prone person sleepless nights."

Worry has been linked to physical health problems. In research at the University of Leiden in The Netherlands, teachers had their heart rate monitored 24 hours-a-day and kept a log of when they had episodes of worrying. Results show that when they were worrying, their heart rate increased by 2.55 beats a minute and variability went down by 5.76 milliseconds. Two hours after the episode, the heart rate was still 1.52 beats per minute higher.

The findings are important because heart rate is a measure of how hard the heart is working and a higher rate means it is having to work harder. Increased rates and reduced heart rate variability have both been linked to a higher risk of heart problems.

While some worrying is necessary and protective, both too little and too much, it seems, can be hazardous.

Excessive worrying is not only potentially unhealthy, it has absolutely no value and purpose.

As the American novelist Alice Caldwell Rice, put it: "It ain't no use putting up your umbrella 'til it rains."