Progress Daily

Place a rat in a cage with an electrified floor and subject it to repeated shocks; it will show many signs of stress, at first flinging itself against the walls with each shock. But after a while, it just sits there apathetically, showing no inclination to escape from its painful prison. When autopsied, it will be found to have oversized adrenal glands and, frequently, stomach ulcers, both indicating serious stress.

Now repeat the experiment, but with a wooden stick in the cage alongside the rat. When shocked, the rat chews on the stick, and as a result, it can endure its experience much longer without burnout. At autopsy, its adrenal glands are smaller, stomach ulcers fewer.

Put 2 rats in the electrified cage. Shock them both. They snarl and fight. At autopsy, their adrenal glands are normal, and, even though they have experienced numerous shocks, they have no ulcers.

Recently physiologists have uncovered the hormonal basis for such behavior. Animals and people subjected to attack or threat experience “subordination stress,” as a result of which their adrenal hormones go up, along with blood pressure and the probability of developing ulcers. But when given the opportunity to “take it out” on someone else, victims show no sign of stress.

“The Targets of Aggression,” by David P. Barash

Studies have shown that the IQs of breastfed children are, on average, about 6 points higher than those given baby formulas.

Terrie Moffitt and Avshalom Caspi suspected the involvement of a gene called FADS2, which regulates the metabolism of long-chain polyunsaturated fatty acids — which are important for the growth of nerve cells and are abundant in human milk. FADS2 comes in two varieties, known as C and G, and the researchers wondered if these two varieties interacted differently with breast milk.

To find out (see “Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism“), they drew on data from two groups of people, one in New Zealand (born in 1972 and 1973) and one in Britain (born in 1994 and 1995).

The researchers found that the increase in intelligence associated with breastfeeding only happened to people who had inherited at least one copy of the C version of FADS2. (Most genes are present as two copies, one inherited from the mother and one from the father.) The effect did not depend on parental social class or IQ, nor on birthweight (low birthweight has been linked to lower IQ). And the difference in IQ was preserved into adulthood.

Only about 10% of the population is double-G.

“The nature of nurture,” The Economist

The ultimatum game brings out conflicting impulses: a researcher offers two players a set amount of money and explains that if they agree on how to divvy it up they will keep that money for themselves. If they don’t, neither will get anything. One player then offers the other a split. Most players reject a patently unfair division — such as offering only $4 out of a total of $20. Yet, self interest would argue that even $4 is better than nothing, which is what will otherwise result.

Daria Knoch and economist Ernst Fehr studied 52 young men in the ultimatum game. The researchers specified the amounts that could be offered - ranging from four to 10 Swiss francs out of 20 - and had computers randomly select some of the offers. This helped distinguish between the recipients demand for reciprocity - only applicable when another human being is in control - and a general resistance to unfair offers. The scientists divided the recipients into 3 groups: those who would receive transcranial magnetic stimulation (TMS) to suppress electrical activity in the right side of their prefrontal cortices, those who would receive the treatment on the left side and, as controls, those who would receive no stimulation.

45% of the men who experienced TMS on the right side of their prefrontal cortex accepted the most unfair offers - a split of 16 to 4 - compared with just 15% of those whose left side had been stimulated and 9% of the controls. 37% of those who underwent right side stimulation accepted all unfair offers - judged as any split less than 10 to 10 - whereas no one was so accepting in the other groups. And they made the decision to accept an unfair offer as quickly as a fair one, while their colleagues needed much longer to decide. This marks the first time that brain researchers have controlled a specific behavior by using TMS on a specific region of the brain. It takes at least 15 minutes of direct application to the skull to induce the changes, and they only last a short while.

“Selfish Impulse Set Free by Magnetic Pulse to Brain,” by David Biello

In transcranial magnetic stimulation (”TMS”), a coil of wire is placed near the head. Alternating current flowing through the coil induces a magnetic field with a strength of up to 2.5 teslas (one tesla is 20,000 times the strength of the earth’s magnetic field). The field passes harmlessly through the skull and influences the electrical signals passing among neurons in the brain.

Physicians hold the coil close to whichever brain region they are interested in stimulating. In repetitive transcranial magnetic stimulation (rTMS), the current is switched on and off from one to 100 times a minute, which creates a series of magnetic impulses. A low frequency will block neural activity, yet higher frequencies will stimulate it. The latter appears to alleviate depression.

Subjects sometimes describe as a slight pull on the scalp. Mild headaches are common side effects. A few patients have had seizures.

Molecular studies by Armand Hausmann suggest that TMS stimulates neuronal factors that are known to aid in cell growth.

When Alvaro Pascual-Leone directed a coil at the language center of his participants, they suddenly could not utter a single word. After 5 half-hour treatment cycles by Peter Eichhammer, some tinnitus sufferers reported a substantial decrease in background noise, which for a few individuals lasted up to 6 months.

Steve Cole and John Cacioppo, used a “gene chip” to look at the DNA of isolated people and found that people who described themselves as chronically lonely have distinct patterns of genetic activity, almost all of it involving the immune system.

The study does not show which came first — the loneliness or the physical traits.

Many studies of large populations have shown that people who describe themselves as lonely or as having little social support are more likely to die prematurely and to have infections, high blood pressure, insomnia and cancer.

When the researchers studied and compared all 22,000 human genes, 209 stood out in the loneliest people.

Many of the these genes seemed to be involved in the basic immune response to tissue damage and others were involved in the production of antibodies (the tag the body uses to mark microbes or damaged cells for removal), suggesting that the loneliest people had unhealthy levels of chronic inflammation, which has been associated with heart and artery disease, arthritis, Alzheimer’s, etc.

“Sick? Lonely? Genes tell the tale,” Reuters

Worldwide, 10% to 40% of children grow up in households with no father. In the U.S., more than half of divorced fathers lose contact with their kids within a few years. By the end of 10 years, as many as two-thirds of them have drifted out of their children’s lives. According to a 1994 study by the Children’s Defense Fund, men are more likely to default on a child-support payment (49%) than a used-car payment (3%). In intact U.S. families, fathers spend an average of less than an hour a day (up from 20 minutes a few decades ago) focussed on their children.

Homo sapiens produces the most slowly maturing young of all mammals. Among foraging humans, children need 19 years — and consume 13 million calories — before producing more food for their community than they take from it, according to Hillard Kaplan. There is more variation in fathering styles across human cultures than in any other primate species.

One thing that draws a human male to a child of his is that, hormonally speaking, men are similar to women, during the period approaching a child’s birth and its infancy. As in some other mammalian species, human males have high levels of prolactin (a hormone usually associated with lactating mothers) toward the end of a partner’s pregnancy.

Katherine Wynne-Edwards and Anne Storey have shown that new or expectant fathers holding either their baby or a doll wrapped in a blanket that recently held — and still smells of — a newborn experienced a rise in prolactin and cortisol (a stress hormone associated with mothering) and a drop in testosterone. When the men listened to a tape of a crying newborn and were shown a videotape of a newborn struggling to nurse, the ones who reported the greatest urge to comfort the baby were the ones whose hormone levels had changed the most.

Dads have to spend time close to babies for hormones to kick in.

In traditional societies, 40% of offspring might die before age 5.

Among some West African Mandinka, the help of a maternal grandmother has been linked with a halving of the under-5 mortality rate. Similar benefits were shown in Finnish farming communities in the 18th century.

It was this cooperative system that allowed mothers to have more babies than they could support and fathers to vary in how they cared for them.

“The Psychology of Fatherhood,” by Sarah Blaffer Hrdy

A small study (”Efficacy of physical activity in the adjunctive treatment of major depressive disorders“) has found that depressed women who exercised had significant improvements in their symptoms over the next 8 months. Those who didn’t exercise showed only marginal improvements.

Before the study, all of the women had tried taking antidepressant medication for at least 2 months but had failed to improve.

The study included 30 women ages 40 to 60 who’d been diagnosed with major depression. The researchers randomly assigned the women to either stick with antidepressants alone or to start an exercise program. All of the patients continued to take their medication.

The exercisers worked out as a group twice a week for one hour, using cardio-fitness machines. At the beginning of the study and 8 months later, women in both groups completed standard measures used to assess depression severity.

Women in the exercise group showed marked improvements in their depression symptoms, while those on medication alone made only modest gains.

Physical activity seems to affect some key nervous system chemicals — norepinephrine and serotonin — that are targets of antidepressant drugs, as well as brain neurotrophins, which help protect nerve cells from injury and transmit signals in brain regions related to mood.

“Exercise may help with hard-to-treat depression,” Scientific American

Unremitting stress damages the immune system. Two years ago, researchers at UCSF looked at white blood cells from a group of mothers whose children suffered from chronic disorders like autism or cerebral palsy. They found clear signs of accelerated aging in those study subjects who had cared the longest for children with disabilities or who reported the least control over their lives.

The changes took place in microscopic structures called telomeres, which are often compared to the plastic wrappers on the ends of shoelaces and which keep chromosomes from shredding. As a general rule, the youngest cells boast the longest telomeres. But telomeres in the more stressed-out moms were significantly shorter than those of their counterparts, making them, from a genetic point of view, anywhere from nine to 17 years older than their chronological age.

People with low self-esteem are more vulnerable to stress. According to Jens Pruessner, the hippocampus — a finger-size structure located deep in the brain, which helps you form new memories and retrieve old ones — is particularly sensitive to the amount of cortisol flooding your cerebrum. So when cortisol levels begin to rise, the hippocampus sends a set of signals that help shut down the cortisol cascade.

Using several different types of brain scans, Pruessner has shown that people who test below average on self-esteem also tend to have smaller-than-average hippocampi. (The differences become clear only when you compare groups of people.)

Samuel Melamed: “[I]f there is no relief [from stress] and the cortisol stays up for long periods of time, the body stops responding and readjusts the level.”

If you provide mice with an escape route, they typically learn quickly how to avoid a mild electrical shock that occurs a few seconds after they hear a tone. But if the escape route is blocked whenever the tone is sounded, and new shocks occur, the mice will eventually stop trying to run away. Later, even after the escape route is cleared, the animals simply freeze at the sound of the tone– despite the fact that they once knew how to avoid the associated shock.

Animal research has shown that there is a relatively small window for reversing the physiological effects of chronic stress. And once a person’s cortisol level gets completely blunted, it may stay that way for years.

“6 Lessons for Handling Stress,” by Christine Gorman

Wendy Demark-Wahnefried recruited 161 men recently diagnosed with prostate cancer, which they split into 4 groups.

One group ate 3 tablespoons of flaxseed each day (by mixing it with yogurt or water, for example) and maintained a low-fat diet. Of the remaining 3 groups, one maintained a low-fat diet, another ate flaxseed, and the last was a control that made no lifestyle change.

Most of the men had surgery to remove their prostates within 30 days of enrolling in the trial.

Demark-Wahnefried examined the DNA of the removed tumour cells.

The analysis revealed that 50% fewer of the tumour cells from men assigned to eat flaxseed - with or without maintaining a low-fat diet - were actively dividing compared with those of their control counterparts. Maintaining a low-fat diet alone did not appear to affect tumour growth.

Demark-Wahnefried speculates that replacing omega-6 molecules in the body with omega-3 compounds may send chemical signals that tell cells not to divide.

There are about 4 grams of omega-3 fatty acids in 3 tablespoons of flaxseed.

Demark-Wahnefried notes that flaxseed can have a laxative effect.

“Flaxseed may slow prostate tumour growth,” by Roxanne Khamsi

In the ultimatum game, one player divides a pot of money between himself and another. The other then chooses whether to accept the offer. If he rejects it, neither player benefits. A stingy offer (one that is less than about a quarter of the total) is, indeed, usually rejected.

One explanation of the rejectionist strategy is that human psychology is adapted for repeated interactions rather than one-off trades. In this case, taking a tough, if self-sacrificial, line at the beginning pays dividends in future rounds of the game. (When one-off ultimatum games are played by trained economists they do tend to accept stingy offers more often than other people would.) Terence Burnham recently gathered a group of male students of microeconomics and asked them to play the ultimatum game.

Dr Burnham’s research budget ran to a bunch of $40 games. When there are many rounds in the ultimatum game, players learn to split the money more or less equally. He also ran a game of one round only, in which proposers could choose only between offering the other player $25 (ie, more than half the total) or $5. Responders could accept or reject the offer. Dr Burnham took saliva samples from all the students and compared the testosterone levels assessed from those samples with decisions made in the one-round game.

The responders who rejected a low final offer had an average testosterone level more than 50% higher than the average of those who accepted. Five of the 7 men with the highest testosterone levels in the study rejected a $5 ultimate offer but only one of the 19 others made the same decision.

A high testosterone level is correlated with social dominance in many species.

“Money isn’t everything,” The Economist