The ambulance siren screams it’s warning to get out of the way. You can’t move your car because you’re stuck in a bumper-to-bumper traffic jam that reaches as far as the eye can see. There must be an accident up ahead. Meanwhile the road construction crew a few feet from your car is jack-hammering the pavement. You are about to enter the stress zone.

Inside your body the alert goes out.

"Attention all parasympathetic forces. Urgent. Adrenal gland missile silos mounted atop kidneys have just released chemical cortisol weapons of brain destruction. Mobilize all internal defenses. Launch immediate counter-calm hormones before hippocampus is hammered by cortisol."

Hormones rush to your adrenal glands to suppress the streaming cortisol on its way to your brain. Other hormones rush to your brain to round up all the remnants of cortisol missles that made it to your hippocampus. These hormones escort the cortisol remnants back to Kidneyland for a one-way ride on the Bladderhorn. You have now reached metabolic equilibrium, also known as homeostasis.

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When a danger finally passes or the perceived threat is over, your brain initiates a reverse course of action that releases a different bevy of biochemicals throughout your body. Attempting to bring you back into balance, your brain seeks the holy grail of "homeostasis," that elusive state of metabolic equilibrium between the stimulating and the tranquilizing chemical forces in your body.

If either the one of the stimulating or tranquilizing chemical forces dominates the other without relief, then you will experience an on-going state of internal imbalance. This condition is known as stress. And it can have serious consequences for your brain cells.

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The sympathetic nervous system (SNS) turns on the fight or flight response. In contrast, the parasympathetic nervous system (PNS) promotes the relaxation response.

Like two tug-of-war teams skillfully supporting their rope with a minimum of tension, the SNS and PNS carefully maintain metabolic equilibrium by making adjustments whenever something disturbs this balance.

The strongmen on these teams are hormones, the chemical messengers produced by endocrine glands. Named after a Greek word meaning "to set in motion," hormones travel through the bloodstream to accelerate or suppress metabolic functions.

The trouble is that some stress hormones don't know when to quit pulling. They remain active in the brain for too long – injuring and even killing cells in the hippocampus, the area of your brain needed for memory and learning. Because of this hierarchical dominance of the SNS over the PNS, it often requires conscious effort to initiate your relaxation response and reestablish metabolic equilibrium.

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The primary area of the brain that deals with stress is its limbic system. Because of its enormous influence on emotions and memory, the limbic system is often referred to as the emotional brain. It is also called the mammalian brain, because it emerged with the evolution with our warm-blooded relatives, and marked the beginning of social cooperation in the animal kingdom.

Whenever you perceive a threat, imminent or imagined, your limbic system immediately responds via your autonomic nervous system – the complex network of endocrine glands that automatically regulates metabolism.

The term "stress" is short for distress, a word evolved from Latin that means "to draw or pull apart." The Romans even used the term districtia to describe "a being torn asunder." When stressed-out, most of us can probably relate to this description.

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Your sympathetic nervous system does an excellent job of rapidly preparing you to deal with what is perceived as a threat to your safety. Its hormones initiate several metabolic processes that best allow you to cope with sudden danger.

Your adrenal glands release adrenaline (also known as epinephrine) and other hormones that increase breathing, heart rate, and blood pressure. This moves more oxygen-rich blood faster to the brain and to the muscles needed for fighting or fleeing. And, you have plenty of energy to do either, because adrenaline causes a rapid release of glucose and fatty acids into your bloodstream. Also, your senses become keener, your memory sharper, and you are less sensitive to pain.

Other hormones shut down functions unnecessary during the emergency. Growth, reproduction, and the immune system all go on hold. Blood flow to the skin is reduced. That's why chronic stress leads to sexual dysfunction, increases your chances of getting sick, and often manifests as skin ailments.
With your mind and body in this temporary state of metabolic overdrive, you are now prepared to respond to a life-threatening situation.

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After a perceived danger has passed, your body then tries to return to normal. But this may not be so easy, and becomes even more difficult with age. Although the hyperactivating sympathetic nervous system jumps into action immediately, it is very slow to shut down and allow the tranquilizing parasympathetic nervous system to calm things down.

Once your stress response has been activated, the system wisely keeps you in a state of readiness.

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Bear in mind that an appropriate stress response is a healthy and necessary part of life. One of the things it does is to release norepinephrine, one of the principal excitatory neurotransmitters. Norepinephrine is needed to create new memories. It improves mood. Problems feel more like challenges, which encourages creative thinking that stimulates your brain to grow new connections within itself.

Stress management is the key, not stress elimination. The challenge in this day and age is to not let the sympathetic nervous system stay chronically aroused. This may require knowledge of techniques that work to activate your relaxation response.

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Some kinds of acute stress are beneficial. For example, Ohio State University researchers found that stress from engaging in a memory task activated the immune system, whereas the stress from passively watching a violent video weakened immunity (as measured by salivary concentration of SIgA, a major immune factor).

Their results suggest that deadlines and challenges at work, even if annoying for a short time, could be a good thing that helps strengthen the body's defenses.¹

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Stress can dramatically increase the ability of chemicals to pass through the blood-brain barrier. During the Gulf War, Israeli soldiers took a drug to protect themselves from chemical and biological weapons.

Normally, it should not have crossed the BBB, but scientists learned that the stress of war had somehow increased the permeability of the BBB. Nearly one-quarter of the soldiers complained of headaches, nausea, and dizziness – symptoms which occur only if the drug reaches the brain.

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Permeating the human brain are 400 miles of blood vessels – providing nutrients, fuel, and oxygen, while removing waste and excess heat. The capillaries in this vascular system also comprise what is called the blood-brain barrier (BBB), a protective network unique to the central nervous system.

Present in all vertebrate brains, the BBB is laid down within the first trimester of human fetal life. Although far from perfect, it does shield neurons from some poisons, viruses, and other toxins in the bloodstream – as well as from unpredictable fluctuations in normal blood chemistry.

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The primary BBB is formed by cerebral capillaries that are different from those elsewhere in the body. Most capillary walls contain tiny openings called "slit pores" that permit molecules to diffuse easily into the surrounding tissue – somewhat like a soaker hose.

Cerebral capillaries do not have these clefts. They are lined with firmly connected endothelial cells, whose intercellular junctions are as tight as any in biology. Molecules must pass through cerebral capillary walls by active transport with certain carrier molecules, instead of through slit pores.

The secondary BBB surrounds the cerebral capillaries. It is composed of "glial" cells, the other family of brain cells that outnumber neurons by a factor of ten. Certain types of glial cells form a buffer between the brain's capillaries and its neurons. These support cells further obstruct toxins from the bloodstream, while regulating the correct flow of necessary nutrients.

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Human infants are all ears. They are very conscious of sound and focus on every word they hear, so they can learn to speak. Loud noises trigger a "startle response" – large movements of the baby's limbs and torso – even while in the womb. Until 18 months old, infants react strongly to distress sounds from other infants.

Crucial to survival, this instinctual reaction to noise enables us to go from a deep sleep to a quick sprint in a matter of seconds. . . or to do battle with surprising strength. Today, however, our stress response is getting knee-jerked around by all the bells and whistles of modern civilization. From the clatter and jar of diesels and dump trucks, to chest-thumping teenage car tunes, noise is almost impossible to block. It's very uncontrollability further adds to the stressful impact.

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A disorder of the heart's electrical system, known as the Long QT Syndrome (LQTS), is a life-threatening disorder that can be triggered by a loud noise. In people with LQTS, the electrical recovery of their heart takes longer than normal after each heart beat.

Dr. G. Michael Vincent, an expert in LQTS, says this prolongation "renders patients vulnerable to a very fast, abnormal heart rhythm. . . no blood is pumped out from the heart, and the brain quickly becomes deprived of blood, causing the usual symptoms of sudden loss of consciousness (syncope) and sudden death."

Acoustic stress – such as awakening because of a loud noise – can trigger an episode. Vincent notes that "symptoms usually occur during physical exertion or emotional excitement like anger, fear, or startle" Common examples of startle events include sudden noise, like sirens, the telephone, and the alarm clock.

LQTS is estimated to cause as many as 3,000 deaths in the U.S. each year – mostly in children and young adults – says Vincent, who founded the Sudden Arrhythmia Death Syndromes Foundation (www.sads.org).

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Stress can exacerbate a number of psychiatric disorders, many of which are associated with the prefrontal cortex (PFC), the area of the brain unique to humans. A Yale University study looked at the effects of noise stress on brain function in monkeys. Results indicate that stress impairs PFC cognitive function through its influence on dopamine, a key neurotransmitter that's involved in many brain disorders, including ADHD and Parkinson's disease.

The researchers think that "stress may take the PFC 'off-line' to allow more habitual responses . . . to regulate behavior. This mechanism may have survival value, but may often be maladaptive in human society, contributing to the vulnerability of the PFC in many neuropsychiatric disorders."²

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Because of the immediate need to respond to noise threats, the conscious mind is bypassed. It may not be fast enough to deal with a situation that could be a matter of life and death.

University College London researchers observed the process using functional MRI brain scans of human test subjects who had been stressed by an unpleasantly loud noise that was combined with visual images. Even when a fearful stimulus was present only at the unconscious level, the threat signal triggered activity in the attention center of the cerebral cortex, where the fear response is then channeled to other parts of the brain that prepare the body in the classic flight or fight reaction.

Lead researcher Jorge Armony said, "It makes perfect sense – you can't stop and think about certain things, you have to react."³

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Even sounds you can't hear can have a powerful affect on your nervous system. One example is the "infrasound" in the roar of a tiger.

A tiger's intimidating roar has the power to paralyze animals. Even experienced human trainers are stunned. "We suspect that this is caused by the low frequencies and loudness of the sound," says Elizabeth von Muggenthaler, a bioacoustician from the Fauna Communications Research Institute in North Carolina. "Humans can hear frequencies from 20 hertz to 20,000 hertz, but whales, elephants, rhinos, and tigers can produce sounds below 20 hertz."

The shocking power of a tiger's roar is one example of how humans react to a sound they cannot detect with their ears. But what about all the noise generated by our modern world – including the multitude of ultrasounds whose frequencies are above 20,000 hertz and beyond our hearing range?

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In the first study of its kind, von Muggenthaler and her colleagues recorded every growl, hiss, chuff, and roar of 24 tigers at the Carnivore Preservation Trust in Pittsboro, North Carolina, and the Riverbanks Zoological Park in Columbia, South Carolina. The bioacousticians found that tigers can create sounds at about 18 hertz, and when tigers roar they can create frequencies significantly below this.⁴

This unheard, low-pitched infrasound can travel long distances – permeating buildings, cutting through dense forests, and even passing through mountains.

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Not just loud or sudden noises provoke a stress response. Chronic low-level noise also negatively influences the brain and behavior. Whether from the road or in the office, low-intensity noise has a subtle yet insidious effect on our health and well-being.

Noise at home or school can affect children's ability to learn. Compared to kids from quieter neighborhoods, children living near airports or busy highways tend to have lower reading scores and develop language skills more slowly. Psychiatric hospitalizations are higher in noisy communities. Bad moods, lack of concentration, fatigue, and poor work performance can result from continual exposure to unpleasant noise.⁵

According to Dr. Alice H. Suter, an audiologist at the National Institute for Occupational Safety and Health: "Included in noise-related problems are high blood pressure, peptic ulcers, cardiovascular deaths, strokes, suicides, degradation of the immune system, and impairment of learning. Noise is also associated with an increase in aggression and a decrease in cooperation."⁶

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Even everyday traffic noise can harm the health and well-being of children. In the first study to look at the non-auditory health effects of typical ambient community noise, it was shown that chronic low-level noise from local traffic raised levels of stress hormones in children, as well as their blood pressure and heart rates.

"We found that even low-level noise can be a stressor. It elevates psychophysiological factors and triggers more symptoms of anxiety and nervousness," says environmental psychologist Gary Evans of Cornell University, an international expert on environmental stress, such as noise, crowding, and air pollution.

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Evans and his European colleagues analyzed data on 115 fourth-graders in Austria. Half the children lived in quiet areas – below 50 decibels (dB), the sound level of a clothes dryer or a quiet office. Half lived in a noisier residential area – above 60 dB, about the intensity of an average dishwasher or raised voices.

"We are really not looking at loud kinds of noise. They are typical levels found throughout neighborhoods in Europe," says Evans. The non-auditory effects of noise, however, appear to occur at levels far below those required to damage hearing.

The children in noisier neighborhoods experienced higher overnight levels of the stress hormone cortisol, marginally higher resting systolic blood pressure, and greater heart rate reactivity to a stress test – all signs of modestly elevated physiological stress.

Background noise had a significant effect on stress levels, said Lercher. Therefore, chronic exposure to nearby sounds from roads and train lines are a concern.

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When children have no control over prolonged exposure to noise, it can lead to "learned helplessness" syndrome – a condition linked to forms of depression and to poverty. "It's a pretty pervasive phenomenon," says Evans. He found that "girls exposed to the traffic noise become less motivated, presumably from the sense of helplessness that can develop from noise they couldn't control."

Women respond differently to loud noise, too. A study at Texas A&M University found that "women have a lower threshold to experience noise as stressful," according to psychologist Dr. Mary W. Meagher. "Our data suggest that women may be more sensitive to noise stress than men." (While the women in the study were more easily "frightened" by a loud unexpected noise, the men were only more "startled.")⁷

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Are you feeling stressed but don’t know why? Could noise be the problem? Are you aware of the chronic sources of noise in your everyday environment?

Check these reports and studies to find out if noise may be effecting you.

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"The U.S. Census Bureau reports that Americans cite noise – more than crime, litter, traffic, or inefficient government – as the biggest problem affecting their neighborhoods. 138 million people are regularly exposed to noise levels labeled as excessive by the Environmental Protection Agency."⁸

British investigators found that a greater amount of neighborhood problems, including noise, was associated with residents being three times as likely to say their physical function was impaired and twice as likely to report poorer health. "What we think is happening is that neighborhood stress influences the biological processes that promote disease risk," said Dr. Andrew Steptoe of University College London.⁹

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Gary Evans and environmental psychologists at Cornell found that low-level noise in open-style offices seems to result in higher levels of stress, and lower task motivation.

Forty experienced female clerical workers (average age 37) were assigned for three hours to either a quiet office or one with low-intensity office noise (including speech). The workers in the noisy office experienced significantly higher levels of stress (as measured by urinary epinephrine, a stress hormone), made 40% fewer attempts to solve an unsolvable puzzle, and made only half as many ergonomic adjustments to their workstations, compared to their colleagues in quiet offices.

Interestingly, however, the workers themselves did not report higher levels of stress in the noisy office.

"But just because people fail to report that environmental conditions are negative, we can't assume that there are no adverse impacts," Evans says.

"Our findings resemble those in studies of very noisy environments in that we found that realistic, open-office noise has modest but adverse effects on physiological stress and motivation," says Evans, and might contribute significantly to health problems such as heart disease (due to elevated levels of epinephrine) and musculoskeletal problems. "Even low levels of noise can have a potentially stressful effect."¹⁰

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10 million people have hearing loss because of "toxic noise" in the workplace. The Deafness Research Foundation defines toxic noise as any noise that can damage or destroy hearing. It is present in the workplace of approximately 30 million Americans.

Although preventable, toxic noise is the most common occupational disease and the second most self-reported occupational injury, says Elizabeth Foster, the director of the National Campaign for Hearing Health.¹¹

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Have you ever forgotten something during a stressful situation that you should have remembered? Cortisol also interferes with the function of neurotransmitters, the chemicals that brain cells use to communicate with each other.

Excessive cortisol can make it difficult to think or retrieve long-term memories. That's why people get befuddled and confused in a severe crisis. Their mind goes blank because "the lines are down." They can't remember where the fire exit is, for example.

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Stress hormones divert blood glucose to exercising muscles, therefore the amount of glucose – hence energy – that reaches the brain's hippocampus is diminished. This creates an energy crisis in the hippocampus which compromises its ability to create new memories.

That may be why some people can't remember a very traumatic event, and why short-term memory is usually the first casualty of age-related memory loss resulting from a lifetime of stress.

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In an animal study, rats were stressed by an electrical shock, and then made to go through a maze that they were already familiar with. When the shock was given either four hours before or two minutes before navigating the maze, the rats had no problem. But, when they were stressed by a shock 30 minutes before, the rats were unable to remember their way through the maze.

This time-dependent effect on memory performance correlates with the levels of circulating cortisol, which are highest at 30 minutes. The same thing happened when non-stressed rats were injected with cortisol. In contrast, when cortisol production was chemically suppressed, then there were no stress-induced effects on memory retrieval.

According to James McGaugh, director of the Center for the Neurobiology of Learning and Memory at the University of California, Irvine, "This effect only lasts for a couple of hours, so that the impairing effect in this case is a temporary impairment of retrieval. The memory is not lost. It is just inaccessible or less accessible for a period of time."¹²

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Normally, in response to stress, the brain's hypothalamus secretes a hormone that causes the pituitary gland to secrete another hormone that causes the adrenals to secrete cortisol. When levels of cortisol rise to a certain level, several areas of the brain – especially the hippocampus – tell the hypothalamus to turn off the cortisol-producing mechanism. This is the proper feedback response.

The hippocampus, however, is the area most damaged by cortisol. In his book Brain Longevity, Dharma Singh Khalsa, M.D., describes how older people often have lost 20-25% of the cells in their hippocampus, so it cannot provide proper feedback to the hypothalamus, so cortisol continues to be secreted. This, in turn, causes more damage to the hippocampus, and even more cortisol production. Thus, a Catch-22 "degenerative cascade" begins, which can be very difficult to stop.

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Studies done by Dr. Robert M. Sapolsky, Professor of Neurology and Neurological Sciences at Stanford University, showed that lots of stress or exposure to cortisol accelerates the degeneration of the aging hippocampus.

And, because the hippocampus is part of the feedback mechanism that signals when to stop cortisol production, a damaged hippocampus causes cortisol levels to get out of control – further compromising memory and cognitive function. The cycle of degeneration then continues. (Perhaps similar to the deterioration of the pancreas-insulin feedback system.)

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The study was titled "Cortisol levels during human aging predict hippocampal atrophy and memory deficits". A third of the 60 volunteers, who were between ages 60 and 85, had chronically high cortisol levels, a problem that seems to be fairly common in older people.¹³

The size of the hippocampus averaged 14% smaller in one group and showed high and rising cortisol levels, compared to a group with moderate and decreasing levels. The small hippocampus group also did worse at remembering a path through a human maze and pictures they'd seen 24 hours earlier and – two tasks that use the hippocampus.

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Using magnetic resonance imaging, Mayo Clinic researchers found that specific changes in the hippocampus were linked to changes in behavior associated with aging and Alzheimer's disease. "When certain parts of the hippocampus shrink or deteriorate, specific, related memory abilities are affected," says neurologist Ronald C. Petersen, the principal author of the study.

Furthermore, individuals with a shrunken hippocampus tend to progress more rapidly towards Alzheimer's.

"In earlier studies we were able to show that the volume of the hippocampus could help diagnose early Alzheimer's disease or help predict which patients may develop Alzheimer's disease in the future. Now we can look specifically at which part or parts of the hippocampus are affected and match that with particular memory functions which are impaired in that particular patient," says Dr. Petersen.¹⁴

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In a 2000 human study, McGaugh and researchers at the University of Zurich asked 36 healthy adults to memorize 60 unrelated nouns that were displayed for four seconds each on a computer screen. Study participants were then tested to see if they could remember the words immediately after they learned the list, and then again, a day later.

Subjects took a tablet of cortisone (precursor of cortisol) or a placebo: either one hour before the initial word presentation; just after the word presentation; or one hour before the retention test. (Actual cortisol concentrations in saliva were comparable to levels produced naturally in response to a major stressor.)

Compared to the placebo, the cortisone pills impaired memory – but only when they were taken an hour before the recall test that was given on the next day. Therefore, high levels of this stress hormone impaired memory, but only when people tried to recall old, not recent, memories.

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IThe growth of new brain cells – a process called neurogenesis – is involved in new memory formation. Researchers at Princeton University report that, even in adulthood, thousands of hippocampal neurons were being generated per day.

In animal studies, the number of adult-generated neurons in the hippocampi of rats doubled after they performed specific behavioral tasks and training that involved associative learning. In contrast, tasks that did not require the hippocampus did not stimulate new cell growth.

"All of the species we examined showed evidence of substantial neurogenesis in adulthood," Princeton's Elizabeth Gould said. "These findings indicate that adult-generated hippocampal neurons are specifically affected by, and potentially involved in, associative memory formation."

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London taxi drivers are renowned for their excellent memory in regard to spatial learning – their ability to navigate the vast network of London streets. It turns out they have enlarged hippocampi.¹⁵

Birds with a bigger hippocampus have a longer lasting memory for where they stored their food, compared to birds with a smaller hippocampus. (Their memory capacities were the same, though.) British researchers provided evidence that "the enlargement of the hippocampus in food-storing birds may enable these birds to increase the duration of time over which they can remember spatial information."¹⁶

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Fight-or-flight means that, when confronted by stress, individuals either react with aggressive behavior – such as verbal conflict and more drastic actions – or withdraw or flee from the stressful situation.
"Befriending" methods include talking on the phone with relatives or friends, to such simple social contacts as asking for directions when lost. The "tending" pattern is especially apparent in the differences between fathers' and mothers' behaviors with their children after a stressful workday.

Professor Taylor elaborated: "When the typical father in the study came home after a stressful day at work, he responded to stress by wanting to be left alone, enjoying peace and quiet away from the stress of the office; when office-related stress was particularly acute, a typical response would be to react harshly or create conflict with his wife or children.

"When the typical mother in the study came home from work bearing stress, she was more likely to cope with her bad day by focusing her attention on nurturing her children.

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Men are more vulnerable to the adverse health effects of stress. Men are more likely than women to develop "certain stress-related disorders, including hypertension , aggressive behavior, or abuse of alcohol or hard drugs," Professor Taylor said. "Because the tend-and-befriend regulatory system may, in some ways, protect women against stress, this biobehavioral pattern may provide insights into why women live an average of seven and a half years longer than men."

"The tend-and-befriend pattern exhibited by women probably evolved through natural selection," says Taylor. "Thousands of generations ago, fleeing or fighting in stressful situations was not a good option for a female who was pregnant or taking care of offspring, and women who developed and maintained social alliances were better able to care for multiple offspring in stressful times."

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Oxytocin, a hormone secreted in both men and women as a response to stress, has been shown to calm rats and humans, making them less anxious and more social. "Oxytocin has been studied largely for its role in childbirth. In several animal species, it leads to maternal behavior and to affiliation," Taylor said. Male hormones seem to reduce the effect of oxytocin, but the female hormone estrogen amplifies it.

The UCLA team's findings, were based on analysis of hundreds of biological and behavioral studies of response to stress by thousands of human and animal subjects.¹⁷

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