Primates and patience — the evolutionary roots of self control

A chimpanzee will wait more than two minutes to eat six grapes, but a black lemur would rather eat two grapes now than wait any longer than 15 seconds for a bigger serving.

It’s an echo of the dilemma human beings face with a long line at a posh restaurant. How long are they willing to wait for the five-star meal? Or do they head to a greasy spoon to eat sooner?

A paper published today in the scientific journal Proceedings of the Royal Society B explores the evolutionary reasons why some primate species wait for a bigger reward, while others are more likely to grab what they can get immediately.

"Natural selection has shaped levels of patience to deal with the types of problems that animals face in the wild," said author Jeffrey R. Stevens, a comparative psychologist at the University of Nebraska-Lincoln and the study’s lead author. "Those problems are species-specific, so levels of patience are also species-specific."

Studying 13 primate species, from massive gorillas to tiny marmosets, Stevens compared species’ characteristics with their capacity for “intertemporal choice.” That’s a scientific term for what some might call patience, self-control or delayed gratification.

He found the species with bigger body mass, bigger brains, longer lifespans and larger home ranges also tend to wait longer for a bigger reward.

Chimpanzees, which typically weigh about 85 pounds, live nearly 60 years and range about 35 square miles, waited for a reward for about two minutes, the longest of any of the primate species studied. Cotton-top tamarins, which weigh less than a pound and live about 23 years, waited about eight seconds before opting for a smaller, immediate reward.

The findings are based partially on experiments Stevens performed during the past ten years with lemurs, marmosets, tamarins, chimpanzees and bonobos at Harvard’s Department of Psychology and at the Berlin and Leipzig zoos in Germany. In those experiments, individual animals chose between a tray containing two grapes that they could eat immediately and a tray containing six grapes they could eat after waiting. The wait times were gradually increased until the animal reached an “indifference point” when it opted for the smaller, immediate reward instead of waiting.

Stevens combined those results with those of scientists who performed similar experiments with other primates. He scoured primate-research literature to gather data on the biological characteristics of each species.

In addition to characteristics related to body mass, Stevens analyzed but found no correlation with two other hypotheses for patience: cognitive ability and social complexity.

"In humans, the ability to wait for delayed rewards correlates with higher performance in cognitive measures such as IQ, academic success, standardized test scores and working memory capacity," he wrote. "The cognitive ability hypothesis predicts that species with higher levels of cognition should wait longer than those with lower levels."

But Stevens found no correlation between patience levels and an animal’s relative brain size compared to its body size, the measure he used to quantify cognitive ability.

Researchers also have argued that animals in complex social groups have reduced impulsivity and more patience to adapt to the social hierarchies of dominance and submission. But Stevens did not find correlations between species’ social group sizes and their patience levels.

Stevens said he believes metabolic rates may be the driving factor connecting patience with body mass and related physical characteristics. Smaller animals tend to have higher metabolic rates.

"You need fuel and you need it at a certain rate," he said. "The faster you need it, the shorter time you will wait."

Metabolic rates also may factor in human beings’ willingness to wait. Stevens said human decisions about food, their environment, their health care and even their finances all relate to future payoffs. The mental processes behind those decisions have not yet been well identified.

"To me, this offers us interesting avenues to start thinking about what factors might influence human patience," he said. "What does natural selection tell us about decision making? That applies to humans as well as to other animals."

(Image credit)

Pain’s Benefit to Squid May Hold Clues to Chronic Human Pain

For the longfin inshore squid, pain can mean the difference between life and death, according to a new study. That’s because pain prompts injured squid to behave in ways that help it survive encounters with a fish predator, researchers said.

That finding may also provide hints as to why other animals, including humans, experience long-lasting or chronic pain, behavior experts say.

It’s long been thought that pain causes an animal to act self-protectively, says Robert Elwood, an animal behavior researcher at Queen’s University Belfast who was not involved in the study. Pain teaches an organism to avoid situations that will bring it on. It seems obvious, but it hasn’t really been tested until now, Elwood said in an email interview.

In a study published today in Current Biology, researchers report that the sensitivity with which injured squid reacted to aggressive moves from a predator, in this case a black sea bass, gave the squid better odds of surviving an attack.

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Neurobiologists find chronic stress in early life causes anxiety, aggression in adulthood

In recent years, behavioral neuroscientists have debated the meaning and significance of a plethora of independently conducted experiments seeking to establish the impact of chronic, early-life stress upon behavior – both at the time that stress is experienced, and upon the same individuals later in life, during adulthood.

These experiments, typically conducted in rodents, have on the one hand clearly indicated a link between certain kinds of early stress and dysfunction in the neuroendocrine system, particularly in the so-called HPA axis (hypothalamic-pituitary-adrenal), which regulates the endocrine glands and stress hormones including corticotropin and glucocorticoid.

Yet the evidence is by no means unequivocal. Stress studies in rodents have also clearly identified a native capacity, stronger in some individuals than others, and seemingly weak or absent in still others, to bounce back from chronic early-life stress. Some rodents subjected to early-life stress have no apparent behavioral consequences in adulthood – they are disposed neither to anxiety nor depression, the classic pathologies understood to be induced by stress in certain individuals.

This week, a research team led by Associate Professor Grigori Enikolopov of Cold Spring Harbor Laboratory (CSHL) reports online in the journal Plos One the results of experiments designed to assess the impacts of social stress upon adolescent mice, both at the time they are experienced and during adulthood. Involving many different kinds of stress tests and means of measuring their impacts, the research indicates that a “hostile environment in adolescence disturbs psychoemotional state and social behaviors of animals in adult life,” the team says.

The tests began with 1-month-old male mice – the equivalent, in human terms of adolescents – each placed for 2 weeks in a cage shared with an aggressive adult male. The animals were separated by a transparent perforated partition, but the young males were exposed daily to short attacks by the adult males. This kind of chronic activity produces what neurobiologists call social-defeat stress in the young mice. These mice were then studied in a range of behavioral tests.

“The tests assessed levels of anxiety, depression, and capacity to socialize and communicate with an unfamiliar partner,” explains Enikolopov. They showed that in young mice, chronic social defeat induced high levels of anxiety and helplessness, and less social interaction, including diminished ability to communicate with other young animals. Stressed mice also had less new nerve-cell growth (neurogenesis) in a portion of the hippocampus known to be affected in depression: the subgranular zone of the dentate gyrus.

Another group of young mice was also exposed to social stress, but was then placed for several weeks in an unstressful environment. Following this “rest” period, these mice, now old enough to be considered adults, were tested in the same manner as the other cohort. 

In this second, now-adult group, most of the behaviors impacted by social defeat returned to normal, as did neurogenesis, which retuned to a level seen in healthy controls. “This shows that young mice, exposed to adult aggressors, were largely resilient biologically and behaviorally,” says Enikolopov.

However, in these resilient mice, the team measured two latent impacts on behavior. As adults they were abnormally anxious, and were observed to be more aggressive in their social interactions. “The exposure to a hostile environment during their adolescence had profound consequences in terms of emotional state and the ability to interact with peers,” Enikolopov observes.

What are you scared of?

What do bullies and sex have in common? Based on work by scientists at the European Molecular Biology Laboratory (EMBL) in Monterotondo, Italy, it seems that the same part of the brain reacts to both. In a study published today in Nature Neuroscience, the researchers found that – at least in mice – different types of fear are processed by different groups of neurons, even if the animals act out those fears in the same way. The findings could have implications for addressing phobias and panic attacks in humans.

“We found that there seems to be a circuit for handling fear of predators – which has been described anatomically as a kind of defence circuit – but fear of members of the same species uses the reproductive circuit instead,” says Bianca Silva, who carried out the work, “and fear of pain goes through yet another part of the brain.” 

Working in the lab of Cornelius Gross at EMBL, Silva exposed mice to three threats: another mouse (chosen for being particularly aggressive), a rat (the mouse’s natural predator) or a mild electric shock to the feet. The mice showed the same typical fearful behaviours – running away, freezing – in response to all threats, but their brains painted a different picture. When the scientists mapped the brain activity of mice exposed to the aggressive mouse and the rat, they saw that different parts of a region called the ventromedial hypothalamus (VMH) ‘lit up’ depending on the threat. Fear of the mouse seemed to activate the bottom and sides of the VMH, while fear of the rat seemed to be processed by the VMH’s central and upper areas. This was confirmed when the scientists used drugs to block only the neurons in those ‘rat fear’ areas: mice were no longer afraid of the rat, but were still afraid of the mouse, showing that mice need this brain circuit specifically to process fear of predators.

The human brain has similar circuits, and we too experience different kinds of fear, so the results hint at the possibility of developing more efficient treatments for specific phobias or panic attacks, by targeting only the relevant region of the brain.

For their part, the EMBL scientists plan to probe these fears further. 

“What we’re interested in, in the long-run, is if these results represent a kind of mental state,” says Cornelius Gross, who led the work. “If so, mice should be able to be in that state without expressing it in their behaviour – do they re-live that fear, for example? These are not easy questions to ask in the mouse, but we’re looking into them.”

Gross’s lab are also looking at how these different fears – and the neural circuits that process them – may have evolved. Working with Detlev Arendt’s group at EMBL Heidelberg, they have discovered a similar brain region in a marine worm thought to closely resemble our ancestors from 600 million years ago. Now the team is exploring the possibility that this represents an ancestral core fear circuit that those ancestors handed down to us all, from worms to man.

Chimpanzees communicate with robots

Chimpanzees are willing to socialise with robots, new research reveals. It is the first time that robots have been used to study behaviour in primates other than humans.

The study, by researchers at the University of Portsmouth, shows that chimps respond to even basic movements made by a robot, demonstrating that chimps want to communicate and interact with other ‘creatures’ on a social level. The researchers believe that these basic forms of communication in chimpanzees help to promote greater social bonding and lead to more complex forms of social interaction.

The research, published in Animal Cognition a few days ago, outlines how chimps responded to a human-like robot about the size of a doll. The chimps reacted to small movements made by the robot by inviting play, offering it toys and in one case even laughing at it. They also responded to being imitated by the robot.

The chimps did not appear to be put off by the primitive nature of the gestures but responded in the same way they might to humans or other chimps.

Lead researcher, Dr Marina Davila-Ross, is from the University’s Centre for Comparative and Evolutionary Psychology. She said that the advantage of using a robot in the study was that the chimps could be observed in a controlled but interactive setting while a human researcher was able to examine the chimps’ behaviour without needing to participate. This allowed the researchers to analyse simplest forms of ’social’ interactions.

She said: “It was especially fascinating to see that the chimps recognised when they were being imitated by the robot because imitation helps to promote their social bonding. They showed less active interest when they saw the robot imitate a human.

“Some of the chimps gave the robot toys and other objects and demonstrated an active interest in communicating. This kind of behaviour helps to promote social interactions and friendships. But there were notable differences in how the chimps behaved. Some chimps, for instance, seemed not interested in interacting with the robot and turned away as soon as they saw it.

“In our other studies we have found that humans will also react to robots in ways which suggest a willingness to communicate, even though they know the robots are not real. It’s a demonstration of the basic human desire to communicate and it appears that chimpanzees share this readiness to communicate with others.”

The interactive robot was approximately 45 centimetres high and its head and limbs could move independently while chimpanzee sounds (such as chimpanzee laughter) were sent via a small loudspeaker in its chest area, which was covered by a dress. The chimps first observed a person interacting with the robot which was then turned around to face the chimp while the human researcher looked away to avoid any further communication.

Almost all of the 16 chimpanzees observed showed a level of active communication with the robot, such as gestures and expressions.

Dr Davila-Ross said that the research paves the way for further study using robots to interact with primates and discover more about their social behaviour in a controlled setting, such as how they make friends.

Studying the social side of carnivores

The part of the brain that makes humans and primates social creatures may play a similar role in carnivores, according to a growing body of research by a Michigan State University neuroscientist.

In studying spotted hyenas, lions and, most recently, the raccoon family, Sharleen Sakai has found a correlation between the size of the animals’ frontal cortex and their social nature.

In her latest study, Sakai examined the digitally recreated brains of three species in the Procyonid family – the raccoon, the coatimundi and the kinkajou – and found the coatimundi had the largest frontal cortex. The frontal cortex is thought to regulate social interaction, and the coatimundi is by far the most social of the three animals, often living in bands of 20 or more.

The study, funded by the National Science Foundation, is published in the research journal Brain, Behavior and Evolution.

“Most neuroscience research that looks at how brains evolve has focused primarily on primates, so nobody really knows what the frontal cortex in a carnivore does,” said Sakai, professor of psychology. “These findings suggest the frontal cortex is processing social information in carnivores perhaps similar to what we’ve seen in monkeys and humans.”

Sakai did the most recent study in her neuroscience lab with Bradley Arsznov, a former MSU doctoral student who’s now an assistant professor of psychology at Minnesota State University. Sakai is one of myriad MSU faculty members who help make the university’s brain research portfolio one of the most diverse in the nation.

Her latest study was based on the findings from 45 adult Procyonid skulls acquired from university museum collections (17 coatimundis, 14 raccoons and 14 kinkajous). The researchers used computed tomography, or CT scans, and sophisticated software to digitally “fill in” the areas where the brains would have been.

When they analyzed into the findings, they discovered the female coatimundi had the largest anterior cerebrum volume consisting mainly of the frontal cortex, which regulates social activity in primates. This makes sense, Sakai said, since the female coatimundi is highly social while the male coatimundi, once grown, typically lives on its own or with another male. Also known as the Brazilian aardvark, the coatimundi – or coati – is native to Central and South America.

Raccoons, the most solitary of the three animals, had the smallest frontal cortex. However, raccoons had the largest posterior cerebrum, which contains the sensory area related to forepaw sensation and dexterity – and the raccoon’s forepaws are extremely dexterous and highly sensitive.

The rainforest-dwelling kinkajou had the largest cerebellum and brain stem, areas that regulate motor coordination. This skill is crucial for animals like the kinkajou that live in trees.

Brain size variations in this small family of carnivores appear to be related to differences in behavior including social interaction, Sakai said.

The Split Brain of Honey Bees

Honey bees may have only a fraction of our neurons—just under a million versus our tens of billions—but our brains aren’t so different. Take sidedness. The human brain is divided into right and left sides—our right brain controls the left side of our body and vice versa. New research reveals that something similar happens in bees. When scientists removed the right or left antenna of honey bees, those insects with intact right antennae more quickly recognized bees from the same hive, stuck out their tongues (showing willingness to feed), and fended off invaders. Bees with just their left antennae took longer to recognize bees, didn’t want to feed, and mistook familiar bees for foreign ones. This suggests, the team concludes today in Scientific Reports, that bee brains have a sidedness just like ours do. The researchers also think that right antennae might control other bee behavior, like their sophisticated, mysterious "waggle dance" to indicate food. But there’s no buzz for the left-antennaed.