Posts tagged brain size
Articles and news from the latest research reports.
In a battle of brains, bigger isn’t always better
It’s one of those ideas that seems to make perfect sense: the bigger the brain, the more intelligent the creature. While it is generally true, exceptions are becoming increasingly common. Yet the belief persists even among scientists. Most biologists, for example, assume that rats, with larger brains, are smarter than mice. Cold Spring Harbor Laboratory (CSHL) scientists now challenge this belief. They compared mice and rats and found very similar levels of intelligence, a result that could have powerful implications for researchers studying complex behaviors and learning.
Are rats really smarter than mice? The question is more important than it sounds. For more than a decade, rats have been the rodent of choice for scientists studying how the brain arrives at decisions. They are relatively inexpensive to keep and are the subject of extensive protocols for studying cognitive function. Yet the last few years have seen an explosion in the number of genetic tools available to study their smaller cousins, mice. These tools enable scientists to turn genes on and off within specific populations of neurons – specificity that is critical to understanding how complex behaviors arise. Many investigators have shied away from using these new tools, however, believing that mice simply are not as intelligent as rats.
CSHL Professor Anthony Zador and Santiago Jaramillo, Ph.D., were skeptical. “Mice have the potential to greatly accelerate our research. We didn’t want to discount a very powerful option based on anecdotal evidence of their inferiority,” explains Zador.
The team systematically compared how rats and mice learn to perform a moderately challenging auditory task and found that their performance was similar. “This was a task that tested perceptual ability as well as adaptability, and we were very surprised to see that mice and rats performed about the same,” says Jaramillo, a former postdoctoral researcher in the Zador lab who now heads his own lab at the University of Oregon.
The researchers were able to find only one difference: rats learned somewhat faster than mice. According to Zador and Jaramillo, the training protocol, which was developed and optimized specifically for rats, might account for the slight advantage.
The finding of roughly equal intelligence has broad implications for cognition research. “We’ve found that mice, and all the genetic tools available in them, can be used to study the neural mechanisms underlying decision-making, and they might be suitable for other cognitive tasks as well,” says Zador.
(Source: ekaweb02.eurekalert.org)
Fish study links brain size to parental duties
Male stickleback fish that protect their young have bigger brains than counterparts that don’t care for offspring, finds a new University of British Columbia study.
Stickleback fish are well known in the animal kingdom for the fact that the male of the species, rather than the female, cares for offspring. Male sticklebacks typically have bigger brains than females and researchers wanted to find out if the difference in size might relate to their role as caregivers.
In the study, published recently in Ecology and Evolution, researchers compared regular male sticklebacks to male white sticklebacks, which do not tend to their offspring. They found evidence that this change in male behaviour – giving up caring for the young – occurred at the same time the white stickleback evolved a smaller brain.
“This suggests that regular sticklebacks have bigger brains to handle the brain power needed to care for and protect their young,” says Kieran Samuk, a PhD student in UBC’s Dept. of Zoology and the study’s lead author. “This is one of the first studies to link parental care with brain size.”
The white stickleback is a relatively young species that only diverged from other sticklebacks 10,000 years ago, offering researchers some insight into how quickly brains can evolve.
“Our study tells us that brains might change in very drastic ways in a relatively short period of time. This helps us understand how physical changes such as brain size can lead to more complex behavioural changes,” says Samuk.
Scientists show how bigger brains could help us see better
It has become increasingly common to hear reports that big brains are not necessary, or even an evolutionary fluke. However, the new article found that increases in the size of brain areas, such as the visual cortex, are an essential element of evolution.
As part of the study, the researchers found that an increase in the size of the visual part of the brain in different primate species, including humans, apes, and monkeys, is associated with enhanced visual processing.
It is controversial whether overall brain size can predict intelligence. However the size of specialised areas within the brain is associated with specific changes in behaviour such as reducing the susceptibility to visual illusions and increasing the visual acuity or fine details that can be seen.
First author, Dr Alexandra de Sousa explained: “Primates with a bigger visual cortex have better visual resolution, the precision of vision, and reduced visual illusion strength. In essence, the bigger the brain area, the better the visual processing ability.
“The size of brain areas predicts not only the number of neurons (brain cells) in that area, but also the likelihood of connections between neurons. These connections allow for increasingly complex computations to be made that allow for more accurate, and more difficult, visual perception.”
Co-author, Dr Michael Proulx, Senior Lecturer (Associate Professor) in Psychology, added: “This paper is a novel attempt to bring together the micro and macro anatomy of the brain with behaviour. We link visual abilities, the size of brain areas, and the number of neurons that make up those brain areas to provide a framework that ties brain structure and function together.
“The theory of brain size that we discuss can be tested in the future with more behavioural tests of other species, gathering more comparative neuroanatomical data, and by testing other senses and multi-sensory perception, too. We might be able to even predict how well extinct species could sense the world based on fossil data.”
For the study, Dr Alexandra de Sousa, an expert in brain evolution, provided brain size measurements from her and other’s neuroanatomical research. Dr Michael Proulx, an expert in perception, found psychological studies of visual illusions and visual acuity in the same species or general of animals.
The paper ‘What can volumes reveal about human brain evolution? A framework for bridging behavioral, histometric and volumetric perspectives’ is published today in Frontiers in Neuroanatomy – an online, open access journal.
(Source: bath.ac.uk)
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."
Brain size matters when it comes to animal self-control
Chimpanzees may throw tantrums like toddlers, but their total brain size suggests they have more self-control than, say, a gerbil or fox squirrel, according to a new study of 36 species of mammals and birds ranging from orangutans to zebra finches.
Scientists at Duke University, UC Berkeley, Stanford, Yale and more than two-dozen other research institutions collaborated on this first large-scale investigation into the evolution of self-control, defined in the study as the ability to inhibit powerful but ultimately counter-productive behavior. They found that the species with the largest brain volume – not volume relative to body size – showed superior cognitive powers in a series of food-foraging experiments.
Moreover, animals with the most varied diets showed the most self-restraint, according to the study published in the journal of the Proceedings of the National Academy of Sciences.
“The study levels the playing field on the question of animal intelligence,” said UC Berkeley psychologist Lucia Jacobs, a co-author of this study and of its precursor, a 2012 paper in the journal, Animal Cognition.
This latest study was led by evolutionary anthropologists Evan MacLean, Brian Hare and Charles Nunn of Duke University. The findings challenge prevailing assumptions that “relative” brain size is a more accurate predictor of intelligence than “absolute” brain size. One possibility, they posited, is that “as brains get larger, the total number of neurons increases and brains tend to become more modularized, perhaps facilitating the evolution of new cognitive networks.”
While participating researchers all performed the same series of experiments, they did so on their own turf and on their own animal subjects. Data was provided on bonobos, chimpanzees, gorillas, olive baboons, stump-tailed macaques, golden snub-nosed monkeys, brown, red-bellied and aye-aye lemurs, coyotes, dogs, gray wolves, Asian elephants, domestic pigeons, orange-winged amazons, Eurasian jays, western scrub jay, zebra finches and swamp sparrows.
Food inside a tube used as bait
In one experiment, creatures large and small were tested to see if they would advance toward a clear cylinder visibly containing food – showing a lack of self-restraint – after they had been trained to access the food through a side opening in an opaque cylinder. Large-brained primates such as gorillas quickly navigated their way to the treat or “bait.” Smaller-brained animals did so with mixed results.
Jacobs and UC Berkeley doctoral student Mikel Delgado contributed the only rodent data in the study, putting some of the campus’s fox squirrels and some Mongolian gerbils in their lab through food-foraging tasks.
Mixed results on campus squirrels’ self-restraint
In the case of the fox squirrels, the red-hued, bushy-tailed critters watched as the food was placed in a side opening of an opaque cylinder. Once they demonstrated a familiarity with the location of the opening, the food was moved to a transparent cylinder and the real test began. If the squirrels lunged directly at the food inside the bottle, they had failed to inhibit their response. But if they used the side entrance, the move was deemed a success.
“About half of the squirrels and gerbils did well and inhibited the direct approach in more than seven out of 10 trials,” Delgado said. “The rest didn’t do so well.”
In a second test, three cups (A, B and C) were placed in a row on their sides so the animals could see which one contained food. It was usually cup A. The cups were then turned upside down so the “baited” cup could no longer be seen. If the squirrels touched the cup with the food three times in a row, they graduated to the next round. This time, the food was moved from cup A to cup C at the other end of the row.
“The question was, would they approach cup A, where they had originally learned the food was placed, or could they update this learned response to get the food from a new location?” Delgado said. “The squirrels and gerbils tended to go to the original place they had been trained to get food, showing a failure to inhibit what they originally learned.” Click here for video showing other animals doing the cup test.
“It might be that a squirrel’s success in life is affected the same way as in people,” Jacobs said. “By its ability to slow down and think a bit before it snatches at a reward.”
(Source: newscenter.berkeley.edu)
Gene family linked to brain evolution is implicated in autism severity
The same gene family that may have helped the human brain become larger and more complex than in any other animal also is linked to the severity of autism, according to new research from the University of Colorado Anschutz Medical Campus.
The gene family is made up of over 270 copies of a segment of DNA called DUF1220. DUF1220 codes for a protein domain – a specific functionally important segment within a protein. The more copies of a specific DUF1220 subtype a person with autism has, the more severe the symptoms, according to a paper published in the PLoS Genetics.
This association of increasing copy number (dosage) of a gene-coding segment of DNA with increasing severity of autism is a first and suggests a focus for future research into the condition Autism Spectrum Disorder (ASD). ASD is a common behaviorally defined condition whose symptoms can vary widely – that is why the word “spectrum” is part of the name. One federal study showed that ASD affects one in 88 children.
“Previously, we linked increasing DUF1220 dosage with the evolutionary expansion of the human brain,” says James Sikela, PhD, a professor in the Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine. Sikela led the autism study which also involved other members of his laboratory.
“One of the most well-established characteristics of autism is an abnormally rapid brain growth that occurs over the first few years of life. That feature fits very well with our previous work linking more copies of DUF1220 with increasing brain size. This suggests that more copies of DUF1220 may be helpful in certain situations but harmful in others.”
The research team found that not only was DUF1220 linked to severity of autism overall, they found that as DUF1220 copy number increased, the severity of each of three main symptoms of the disorder — social deficits, communicative impairments and repetitive behaviors – became progressively worse.
In 2012, Sikela was the lead scientist of a multi-university team whose research established the link between DUF1220 and the rapid evolutionary expansion of the human brain. The work also implicated DUF1220 copy number in brain size both in normal populations as well as in microcephaly and macrocephaly (diseases involving brain size abnormalities).
Jack Davis, PhD, who contributed to the project while a postdoctoral fellow in the Sikela lab, has a son with autism and thus had a very personal motivation to seek out the genetic factors that cause autism.
The research by Sikela, Davis and colleagues at the Anschutz campus in Aurora, Colo., focused on the presence of DUF1220 in 170 people with autism.
Strikingly, Davis says, DUF1220 is as common in people who do not have ASD as in people who do. So the link with severity is only in people who have the disorder.
“Something else is at work here, a contributing factor that is needed for ASD to manifest itself,” Davis says. “We were only able to look at one of the six different subtypes of DUF1220 in this study, so we are eager to look at whether the other subtypes are playing a role in ASD.”
Because of the high number of copies of DUF1220 in the human genome, the domain has been difficult to measure. As Sikela says, “To our knowledge DUF1220 copy number has not been directly examined in previous studies of the genetics of autism and other complex human diseases. So the linking of DUF1220 with ASD is also confirmation that there are key parts of the human genome that are still unexamined but are important to human disease.”
In the Human Brain, Size Really Isn’t Everything
There are many things that make humans a unique species, but a couple stand out. One is our mind, the other our brain.
The human mind can carry out cognitive tasks that other animals cannot, like using language, envisioning the distant future and inferring what other people are thinking.
The human brain is exceptional, too. At three pounds, it is gigantic relative to our body size. Our closest living relatives, chimpanzees, have brains that are only a third as big.
Scientists have long suspected that our big brain and powerful mind are intimately connected. Starting about three million years ago, fossils of our ancient relatives record a huge increase in brain size. Once that cranial growth was underway, our forerunners started leaving behind signs of increasingly sophisticated minds, like stone tools and cave paintings.
But scientists have long struggled to understand how a simple increase in size could lead to the evolution of those faculties. Now, two Harvard neuroscientists, Randy L. Buckner and Fenna M. Krienen, have offered a powerful yet simple explanation.
In our smaller-brained ancestors, the researchers argue, neurons were tightly tethered in a relatively simple pattern of connections. When our ancestors’ brains expanded, those tethers ripped apart, enabling our neurons to form new circuits.
Dr. Buckner and Dr. Krienen call their idea the tether hypothesis, and present it in a paper in the December issue of the journal Trends in Cognitive Sciences.
“I think it presents some pretty exciting ideas,” said Chet C. Sherwood, an expert on human brain evolution at George Washington University who was not involved in the research.
Big brains are all in the genes
Scientists have moved a step closer to understanding genetic changes that permitted humans and other mammals to develop such big brains.
During evolution, different mammal species have experienced variable degrees of expansion in brain size. An important goal of neurobiology is to understand the genetic changes underlying these extraordinary adaptations.
The process by which some species evolved larger brains – called encephalization – is not well understood by scientists. The puzzle is made more complex because evolving large brains comes at a very high cost.
Dr Humberto Gutierrez, from the School of Life Sciences, University of Lincoln, UK, led research which examined the genomes of 39 species of mammals with the aim of better understanding how brains became larger and more complex in mammals.
To do this, the scientists focussed on the size of gene families across these species. Gene families are groups of related genes which share similar characteristics, often linked with common or related biological functions. It is believed that large changes in the size of gene families can help to explain why related species evolved along different paths.
The researchers found a clear link between increased brain size and the expansion of gene families related to certain biological functions.
Dr Gutierrez said: “We found that brain size variations are associated with changes in gene number in a large proportion of families of closely related genes. These gene families are preferentially involved in cell communication and cell movement as well as immune functions and are prominently expressed in the human brain. Our results suggest that changes in gene family size may have contributed to the evolution of larger brains in mammals.”
Mammalian species in general tend to have large brains compared to their body size which represent an evolutionary costly adaptation as they require large amounts of energy to function.
Dr Gutierrez explained: “The brain is an extremely expensive organ consuming a large amount of energy in proportion to its volume, so large brains place severe metabolic demands on animals. Larger brains also demand higher parental investment. For example, humans require many years of nurturing and care before their brains are fully matured.”
Dr Gutierrez’s research concluded that variations in the size of gene families associated with encephalization provided an evolutionary support for the specific physiological demands associated with increased brain size in mammals.
(Source: lincoln.ac.uk)
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.
Brain size may signal risk of developing an eating disorder
New research indicates that teens with anorexia nervosa have bigger brains than teens that do not have the eating disorder. That is according to a study by researchers at the University of Colorado’s School of Medicine that examined a group of adolescents with anorexia nervosa and a group without. They found that girls with anorexia nervosa had a larger insula, a part of the brain that is active when we taste food, and a larger orbitofrontal cortex, a part of the brain that tells a person when to stop eating.
Guido Frank, MD, assistant professor of psychiatry and neuroscience at CU School of Medicine, and his colleagues report that the bigger brain may be the reason people with anorexia are able to starve themselves. Similar results in children with anorexia nervosa and in adults who had recovered from the disease, raise the possibility that insula and orbitofrontal cortex brain size could predispose a person to develop eating disorders.
"While eating disorders are often triggered by the environment, there are most likely biological mechanisms that have to come together for an individual to develop an eating disorder such as anorexia nervosa," Frank says.
The researchers recruited 19 adolescent girls with anorexia nervosa and 22 in a control group and used magnetic resonance imaging (MRI) to study brain volumes. Individuals with anorexia nervosa showed greater left orbitofrontal, right insular, and bilateral temporal cortex gray matter compared to the control group. In individuals with anorexia nervosa, orbitofrontal gray matter volume related negatively with sweet tastes. An additional comparison of this study group with adults with anorexia nervosa and a healthy control group supported greater orbitofrontal cortex and insula volumes in the disorder across this age group as well.
The medial orbitofrontal cortex has been associated with signaling when we feel satiated by a certain type of food (so called “sensory specific satiety”). This study suggests that larger volume in this brain area could be a trait across eating disorders that promotes these individuals to stop eating faster than in healthy individuals, before eating enough.
The right insula is a region that processes taste, as well as integrates body perception and this could contribute to the perception of being fat despite being underweight.
This study is complementary to another that found adults with anorexia and individuals who had recovered from this illness also had differences in brain size, previously published in the American Journal of Psychiatry.
(Source: eurekalert.org)