Human Intelligence Secrets Revealed by Chimp Brains

Despite sharing 98 percent of our DNA with chimpanzees, humans have much bigger brains and are, as a species, much more intelligent. Now a new study sheds light on why: Unlike chimps, humans undergo a massive explosion in white matter growth, or the connections between brain cells, in the first two years of life.

The new results, published in the Proceedings of the Royal Society B, partly explain why humans are so much brainier than our nearest living relatives. But they also reveal why the first two years of life play such a key role in human development.

"What’s really unique about us is that our brains experience rapid establishment of connectivity in the first two years of life," said Chet Sherwood, an evolutionary neuroscientist at George Washington University, who was not involved in the study. "That probably helps to explain why those first few years of human life are so critical to set us on the course to language acquisition, cultural knowledge and all those things that make us human."

Chimpanzees

While past studies have shown that human brains go through a rapid expansion in connectivity, it wasn’t clear that was unique amongst great apes (a group that includes chimps, gorillas, orangutans and humans). To prove it was the signature of humanity’s superior intelligence, researchers would need to prove it was different from that in our closest living relatives.

However, a U.S. moratorium on acquiring new chimpanzees for medical research meant that people like Sherwood, who is trying to understand chimpanzee brain development, had to study decades-old baby chimpanzee brains that were lying around in veterinary pathologists’ labs, Sherwood told LiveScience.

But in Japan, those limitations didn’t go into place till later, allowing the researchers to do live magnetic resonance imaging (MRI) brain scans of three baby chimps as they grew to 6 years of age. They then compared the data with existing brain-imaging scans for six macaques and 28 Japanese children.

The researchers found that chimpanzees and humans both had much more brain development in early life than macaques.

"The increase in total cerebral volume during early infancy and the juvenile stage in chimpanzees and humans was approximately three times greater than that in macaques," the researchers wrote in the journal article.

But human brains expanded much more dramatically than chimpanzee brains during the first few years of life; most of that human-brain expansion was driven by explosive growth in the connections between brain cells, which manifests itself in an expansion in white matter. Chimpanzee brain volumes ballooned about half that of humans’ expansion during that time period.

The findings, while not unexpected, are unique because the researchers followed the same individual chimpanzees over time; past studies have instead pieced together brain development from scans on several apes of different ages, Sherwood said.

The explosion in white matter may also explain why experiences during the first few years of life can greatly affect children’s IQ, social life and long-term response to stress.

"That opens an opportunity for environment and social experience to influence the molding of connectivity," Sherwood said.

Re-tuning responses in the visual cortex

New research led by Shigeru Tanaka of the University of Electro-Communications and visiting scientist at the RIKEN Brain Science Institute has shown that the responses of cells in the visual cortex can be ‘re-tuned’ by experience.

Experiments on kittens in the 1960s showed that the primary visual cortex contains neurons that fire selectively to straight lines of specific orientations. These cells are organized into alternating columns that receive inputs from the left or right eye. The kitten experiments also showed that proper brain development is highly dependent on sensory information. Closing one eye altered the organization of the columns, so that those that should have received inputs from the closed eye were reduced in width, whereas those that received inputs from the open eye were much wider than normal.

The normal columnar organization can be restored if the closed eye is re-opened within a critical period of brain development. The effect of sensory experience on the orientation selectivity of neurons in the primary visual cortex is, however, unknown.

To investigate, Tanaka and his colleagues reared mice and fitted them with specially designed goggles through which they can only perceive vertically oriented visual stimuli, for a one-week period, between 3 and 15 weeks of age. Immediately after removing the goggles, they created a ‘window’ in the skull bone lying over the visual cortex to examine the cell response under the microscope.

Rearing the mice in this way had a significant effect on the properties of neurons in the primary visual cortex. The researchers found that the number of cells responding to vertical orientation increased, while the number responding to other orientation decreased. They also found that the extent of these changes depended on the age at which they fitted the animals with the goggles. Mice fitted with the goggles between 4 and 7 weeks of age had more cells that were sensitive to the experienced (vertical) orientation than those fitted later.

These findings show that there is a critical period of plasticity between 4 and 7 weeks, during which cells in the primary visual cortex are particularly sensitive to sensory experience and that plasticity persists in older animals, albeit to a lesser extent. They also suggest that plasticity in younger and older animals involves different mechanisms.

“When we put similar goggles on kittens, the age at which we started goggle rearing determined the reversibility of orientation selectivity,” says Tanaka. “We would now like to clarify the differences and commonalities of the mechanisms in cats and mice.”

A Key Gene for Brain Development

About one in ten thousand babies is born with an abnormally small head. The cause for this disorder – which is known as microcephaly – is a defect in the develoment of the embryonic brain. Children with microcephaly are severely retarded and their life expectancy is low. Certain cases of autism and schizophrenia are also associated with the dysregulation of brain size.

The causes underlying impaired brain development can be environmental stress (such as alcohol abuse or radiation) or viral infections (such as rubella) during pregnancy. In many cases, however, a mutant gene causes the problem.

David Keays, a group leader at the IMP, has now found a new gene which is responsible for Microcephaly. Together with his PhD-student Martin Breuss, he was able to identify TUBB5 as the culprit. The gene is responsible for making tubulins, the building blocks of the cell’s internal skeleton. Whenever a cell moves or divides, it relies on guidance from this internal structure, acting like a scaffold.

The IMP-researchers, together with collaborators at Monash University (Victoria, Australia), were able to interfere with the function of the TUBB5 in the brains of unborn mice. This led to massive disturbances in the stem cell population and impaired the migration of nerve cells. Both, the generation of large numbers of neurons from the stem cell reservoir and their correct positioning in the cortex, are essential for the development of the mammalian brain.

To determine whether the findings are also relevant in humans, David Keays collaborates with clinicians from the Paris-Sorbonne University. The French team led by Jamel Chelly, examined 120 patients with pathological brain structures and severe disabilities. Three of the children were found to have a mutated TUBB5-gene.

This information will prove vital to doctors treating children with brain disease. It will allow the development of new genetic tests which will form the basis of genetic counseling, helping parents plan for the future. By understanding how different genes cause brain disorders, it is hoped that one day scientists will be able to create new drugs and therapies to treat them.

The new findings by the IMP-researchers are published in the current issue of the journal “Cell Reports”. For David Keays, understanding the function of TUBB5 is the key to understanding brain development. “Our project shows how research in the lab can help improve lives in the clinic”, he adds.

The paper “Mutations in the β-tubulin Gene TUBB5 Cause Microcephaly with Structural Brain Abnormalities” is published on December 13, 2012, in the online Journal Cell Reports.

Scientists solve birth and migration mysteries of cortex’s powerful inhibitors, ‘chandelier’ cells

The cerebral cortex of the human brain has been called “the crowning achievement of evolution.” Ironically, it is so complex that even our greatest minds and most sophisticated science are only now beginning to understand how it organizes itself in early development, and how its many cell types function together as circuits.

A major step toward this great goal in neuroscience has been taken by a team led by Professor Z. Josh Huang, Ph.D., at Cold Spring Harbor Laboratory (CSHL). Today they publish research for the first time revealing the birth timing and embryonic origin of a critical class of inhibitory brain cells called chandelier cells, and tracing the specific paths they take during early development into the cerebral cortex of the mouse brain. 

These temporal and spatial sequences are regarded by Huang as genetically programmed aspects of brain development, accounting for aspects of the brain that are likely identical in every member of a given species, including humans. Exceptions to these stereotypical patterns include irregularities caused by gene mutations or protein malfunctions, both of which are now being identified in people with developmental disorders and neuropsychiatric illnesses.

Chandelier cells were first noticed only 40 years ago, and in the intervening years frustratingly little has been learned about them, beyond the fact that they “hang” individually among great crowds of excitatory cells in the cortex called pyramidal neurons, and that their relatively short branches make contact with these excitatory cells.  Indeed, a single chandelier cell connects, or “synapses,” with as many as 500 pyramidal neurons. Noting this, the great biologist Francis Crick decades ago speculated that chandelier cells exerted some kind of “veto” power over the messages being exchanged by the much more numerous excitatory cells in their vicinity.

Fetuses yawn in the womb, according to new research

We know that unborn babies hiccup, swallow and stretch in the womb but new observational research concludes that they also yawn.

The 4D scans of 15 healthy fetuses, by Durham and Lancaster Universities, also suggest that yawning is a developmental process which could potentially give doctors another index of a fetus’ health.

While some researchers have suggested that fetuses yawn, others have disagreed and claim it is simple mouth opening.

But the new research clearly distinguished ‘yawning’ from ‘non-yawn mouth opening’ based on the duration of mouth opening. The researchers did this by using the 4D video footage to closely examine all events where a mouth stretch occurred in the fetus.

Using their newly developed criteria, the research team found that over half of the mouth openings observed in the study were classed as yawns.

The study was carried out on eight female and seven male foetuses from 24 to 36 weeks gestation. The researchers found that yawning declined from 28 weeks and that there was no significant difference between boys and girls in yawning frequency.

Although the function and importance of yawning is still unknown, the study findings suggest that yawning could be linked to fetal development, and as such could provide a further medical indication of the health of the unborn baby.

Teenagers’ brains affected by preterm birth

New research at the University of Adelaide has demonstrated that teenagers born prematurely may suffer brain development problems that directly affect their memory and learning abilities.

The research, conducted by Dr Julia Pitcher and Dr Michael Ridding from the University of Adelaide’s Robinson Institute, shows reduced ‘plasticity’ in the brains of teenagers who were born preterm (at or before 37 weeks gestation).

The results of the research are published in the Journal of Neuroscience.

"Plasticity in the brain is vital for learning and memory throughout life," Dr Pitcher says. "It enables the brain to reorganise itself, responding to changes in environment, behaviour and stimuli by modifying the number and strength of connections between neurons and different brain areas. Plasticity is also important for recovery from brain damage.

"We know from past research that preterm-born children often experience motor, cognitive and learning difficulties. The growth of the brain is rapid between 20 and 37 weeks gestation, and being born even mildly preterm appears to subtly but significantly alter brain microstructure, neural connectivity and neurochemistry.

"However, the mechanisms that link this altered brain physiology with behavioural outcomes - such as memory and learning problems - have remained unknown," Dr Pitcher says.

Neuroscientists Launch 5 Year Study of Music Education and Child Brain Development

Researchers at USC Brain and Creativity Institute will explore the effects of intense music training on cognitive development in LA Phil’s YOLA at HOLA program.

The Los Angeles Philharmonic Association, the USC Brain and Creativity Institute and Heart of Los Angeles (HOLA) are delighted to announce a longitudinal research collaboration to investigate the emotional, social and cognitive effects of musical training on childhood brain development.

The five-year research project, Effects of Early Childhood Musical Training on Brain and Cognitive Development, will offer USC researchers an important opportunity to provide new insights and add rigorous data to an emerging discussion about the role of early music engagement in learning and brain function.

Through a collaboration with the Youth Orchestra Los Angeles at Heart of Los Angeles (YOLA at HOLA) program, a partnership between the LA Phil and HOLA which provides free instruments and musical training to children from the Rampart District of Los Angeles, researchers with the USC Brain and Creativity Institute — led by acclaimed neuroscientists Hanna Damasio and Antonio Damasio – will track how children respond to music from the very onset of their exposure to systematic, high intensity music education.

Delayed Development: 20-Somethings Blame the Brain

Recent research into how the brain develops suggests that people are better equipped to make major life decisions in their late 20s than earlier in the decade. The brain, once thought to be fully grown after puberty, is still evolving into its adult shape well into a person’s third decade, pruning away unused connections and strengthening those that remain, scientists say.

"Until very recently, we had to make some pretty important life decisions about education and career paths, who to marry and whether to go into the military at a time when parts of our brains weren’t optimal yet," says neuroscientist Jay Giedd at the National Institute of Mental Health, whose brain-imaging studies of thousands of young people have yielded many of the new insights. Postponing those decisions makes sense biologically, he says. "It’s a good thing that the 20s are becoming a time for self-discovery."

Such findings are part of a new wave of research into “emerging adulthood,” the years roughly from 18 to 29, which psychologists, sociologists and neuroscientists increasingly see as a distinct life stage. The gap between adolescence and full adulthood is becoming ever wider as more young people willingly or because of economic necessity prolong their education and postpone traditional adult responsibilities. As recently as the 1960s, the average age of first marriage for women in the U.S. was 20, and men 22. Today, the average is 26 for women and 28 for men.

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