Source: University College London

Summary: A recent study shows that, contrary to popular belief, human newborn’s brains aren’t substantially less developed than monkey species. It just appears that way since so much brain growth occurs after birth.

Humans have brains that are typically developed for similar primate species at birth. However, because human brains are so complex than other species, it is mistakenly believed that newborn humans are underdeveloped.

According to lead author Dr. Aida Gomez-Robles of UCL Anthropology, “This new work changes the overall understanding of the evolution of human brain development. Humans seem so much more helpless when they’re young compared to other primates, not because their brains are comparatively underdeveloped but because they still have much further to go.”

Measuring the difference between a species’ birth and adult brain sizes allows scientists to study how their brains evolve.

People appear less mature at birth than other monkey species because humans have smaller brains than other monkeys.

This new study, however, demonstrates that this metric is deceptive because human brain growth is broadly comparable to that of other primates, including chimpanzees, bonobos, gorillas, and orangutans, according to other assessments.

The study casts doubt on accepted theories about how the human brain develops over evolution.

Due to less physical control, it has been believed that humans are born with less developed brains than other animals.

In order for newborn’s heads to fit through their mothers’ birth canal, they had to further develop outside of the womb, which was assumed to be the outcome of an evolutionary compromise.

On the basis of this knowledge, scientists proposed that humans have more pliable brains in their early lives and are more susceptible to external stimuli as they mature, because humans emerged relatively underdeveloped.

It was believed that this early underdevelopment led to increased brain plasticity, which in turn promoted human intelligence.

The reason why human brains take longer to reach their maximum potential than those of other animals

It’s not because their brains are significantly underdeveloped at birth, researchers claim; it’s because their brains develop far more slowly.

Results make it less likely that humans’ superior brain plasticity is the result of being born less developed than other primates. The researchers noted that their findings do not discount the significance of brain plasticity in human evolution.

Scientists examined 140 distinct mammal species including primates, rodents, carnivores and related ancestors of hominins, to understand the human brain.

To comprehend how human brains evolved, researchers analysed the length of fatal gestation in current mammals. The proportion of newborn bodies and brains to those of adults, and the total size of newborn and adult brains

Researchers found that while the brain development of many animal species varies significantly at birth, monkeys’ brains are quite similar.

Both current monkeys and their hominin relatives do not have considerably lower developmental stages at birth than humans.

In the US, the National Institutes of Health and the National Science Foundation funded the study.

Source: Garvan Institute of Medical Research

Summary: Chronic stress can suppress the body’s natural satiety signals, increasing appetite and boosting desires for sweets.

Chronic stress suppresses the brain’s normal satiety-inducing reaction, resulting in continuous reward signals that encourage the consumption of more appetizing food.

This happens in an area of the brain known as the lateral habenula, which normally blocks these reward impulses when it is active.

Professor Herzog, the study’s principal author and visiting scientist at the Garvan Institute, comments, “Our findings reveal stress can override a natural brain response that diminishes the pleasure gained from eating — meaning the brain is continuously rewarded to eat.”

“We showed that chronic stress, combined with a high-calorie diet, can drive more and more food intake as well as a preference for sweet, highly palatable food, thereby promoting weight gain and obesity. This research highlights how crucial a healthy diet is during times of stress.

From mental stress to weight gain:

While some people choose to eat less than usual during stressful times, most people choose calorie-dense, high-sugar, and fatty foods.

To understand what drives these eating behaviours, the team examined how different brain regions responded to long-term stress under varying diets in mouse models.

“We discovered that an area known as the lateral habenula, which is normally involved in switching off the brain’s reward response, was active in mice on a short-term, high-fat diet to protect the animal from overeating. However, when mice are chronically stressed, this part of the brain remains silent — allowing the reward signals to stay active and encourage feeding for pleasure, no longer responding to satiety regulatory signals,” explains first author Dr Kenny Chi Kin Ip from the Garvan Institute.

“We found that stressed mice on a high-fat diet gained twice as much weight as mice on the same diet that were not stressed.”

Researchers discovered that the primary cause of weight gain was the chemical NPY, which the brain normally produces in response to stress.

Stress mice on a high-fat diet consumed fewer comfort foods and gained less weight when the researchers prevented NPY from activating brain cells in the lateral habenula.

Next, in a “sucralose preference test,” the mice were offered the choice of drinking water or water that had been artificially sweetened by the investigators.

“Stressed mice on a high-fat diet consumed three times more sucralose than mice that were on a high-fat diet alone, suggesting that stress not only activates more reward when eating but specifically drives a craving for sweet, palatable food,” says Professor Herzog.

“Crucially, we did not see this preference for sweetened water in stressed mice that were on a regular diet.”

Chronic Stress outweighs a balanced, healthy energy level.

“In stressful situations it’s easy to use a lot of energy and the feeling of reward can calm you down — this is when a boost of energy through food is useful. But when experienced over long periods of time, stress appears to change the equation, driving eating that is bad for the body long term,” says Professor Herzog.

Stress is a major regulator of eating habits that can override the brain’s natural ability to balance energy needs, according to the study.

“This research emphasises just how much stress can compromise a healthy energy metabolism,” says Professor Herzog. “It’s a reminder to avoid a stressful lifestyle, and crucially — if you are dealing with long-term stress — try to eat a healthy diet and lock away the junk food.”

Source: : Karolinska Institute

Summary: Chronic stress, and Alzheimer’s disease may have a link. According to the study, those between the ages of 18 and 65 who had previously been diagnosed with chronic stress were more likely than others to receive a diagnosis of Alzheimer’s disease or mild cognitive impairment.

In Sweden, 160,000 people suffer from dementia, with Alzheimer’s disease being common. This number is increasing as people live longer. The need to uncover additional disease risk factors highlighted by the recent development of several novel early-intervention medications.

Prior research has indicated a potential correlation between depression, dementia, and long-term chronic stress. A history of depression or prolonged stress increases the risk of Alzheimer’s disease development, according to a current study.

According to research, people with prolonged stress were more likely to develop Alzheimer’s disease than people without it. In patients with both conditions, the risk was as high as four times.

There was an equivalent increase in the chance of cognitive impairment. Chronic stress is defined as stress experienced by a patient for more than six months without an opportunity for recovery.

“The risk is still very low and the causality is unknown,” Axel C. Carlsson, a docent at the Karolinska Institute’s Department of Neurobiology, Care Sciences and Society, the study’s final author. “That said, the finding is important in that it enables us to improve preventative efforts and understand links with the other risk factors for dementia.”

All healthcare contacts who were compensated by Region Stockholm were included in the administrative healthcare database used for the study. Patients between 2012 and 2013 who were between the ages of 18 and 65 were the focus of the study.

They found 44,447 individuals who had been diagnosed with depression and/or chronic stress, and they tracked them for eight years to see how many of them developed mild cognitive impairment or Alzheimer’s disease later on.

More people with Alzheimer’s disease than all other 1,362,548 people in the same age had been diagnosed with depression.

“It’s very uncommon for people in this age group to develop dementia, so we need to identify all possible risk factors for the disease,” says Dr Carlsson. “We show here that the diagnosis is more common in people who have suffered chronic stress or depression, but more studies will be required if we’re to demonstrate any causality there.”

Today, the researchers will continue their study, creating questionnaires and cognitive tests to identify people at early risk of dementia.

The Academic Primary Care Center (APC) and Region Stockholm provided funding for this study.