More sophisticated wiring, not just bigger brain, helped humans evolve beyond chimps

August 22, 2012
Chimpanzees

Human and chimp brains look anatomically similar because both evolved from the same ancestor millions of years ago. But where does the chimp brain end and the human brain begin?

A new UCLA study pinpoints uniquely human patterns of gene activity in the brain that could shed light on how we evolved differently than our closest relative. Published Aug. 22 in the advance online edition of Neuron, these ' identification could improve understanding of human like autism and schizophrenia, as well as learning disorders and addictions.

"Scientists usually describe evolution in terms of the human brain growing bigger and adding new regions," explained principal investigator Dr. Daniel Geschwind, Gordon and Virginia MacDonald Distinguished Professor of and a professor of neurology at the David Geffen School of Medicine at UCLA. "Our research suggests that it's not only size, but the rising complexity within brain centers, that led humans to evolve into their own species."

Using post-mortem , Geschwind and his colleagues applied next-generation sequencing and other modern methods to study in humans, and rhesus macaques, a for both chimpanzee and humans that allowed the researchers to see where changes emerged between humans and chimpanzees. They zeroed in on three – the frontal cortex, hippocampus and striatum.

By tracking gene expression, the process by which genes manufacture the amino acids that make up cellular proteins, the scientists were able to search the genomes for regions where the DNA diverged between the species. What they saw surprised them.

"When we looked at gene expression in the frontal lobe, we saw a striking increase in molecular complexity in the human brain," said Geschwind, who is also a professor of psychiatry at the Semel Institute for Neuroscience and Behavior at UCLA.

While the caudate nucleus remained fairly similar across all three species, the frontal lobe changed dramatically in humans.

"Although all three species share a frontal cortex, our analysis shows that how the human brain regulates molecules and switches genes on and off unfolds in a richer, more elaborate fashion," explained first author Genevieve Konopka, a former postdoctoral researcher in Geschwind's lab who is now the Jon Heighten Scholar in Autism Research at University of Texas Southwestern Medical Center. "We believe that the intricate signaling pathways and enhanced cellular function that arose within the frontal lobe created a bridge to human evolution."

The researchers took their hypothesis one step further by evaluating how the modified genes linked to changes in function.

"The biggest differences occurred in the expression of human genes involved in plasticity – the ability of the brain to process information and adapt," said Konopka. "This supports the premise that the human brain evolved to enable higher rates of learning."

One gene in particular, CLOCK, behaved very differently in the human brain. Considered the master regulator of Circadian rhythm, CLOCK is disrupted in mood disorders like depression and bipolar syndrome.

"Groups of genes resemble spokes on a wheel – they circle a hub gene that often acts like a conductor," said Geschwind. "For the first time, we saw CLOCK assuming a starring role that we suspect is unrelated to Circadian rhythm. Its presence offers a potentially interesting clue that it orchestrates another function essential to the human brain."

When comparing the human brain to the non-human primates, the researchers saw more connections among gene networks that featured FOXP1 and FOXP2. Earlier studies have linked these genes to humans' unique ability to produce speech and understand language.

"Connectivity measures how genes interact with other genes, providing a strong indicator of functional changes," said Geschwind. "It makes perfect sense that genes involved in speech and language would be less connected in the non-human primate brains – and highly connected in the ."

The UCLA team's next step will be to expand their comparative search to 10 or more regions of the human, chimpanzee and maque brains.

Explore further: Autism changes molecular structure of the brain, study finds

Related Stories

Autism changes molecular structure of the brain, study finds

May 25, 2011
For decades, autism researchers have faced a baffling riddle: how to unravel a disorder that leaves no known physical trace as it develops in the brain.

Researchers uncover new tools for targeting genes linked to autism

June 21, 2012
UCLA researchers have combined two tools – gene expression and the use of peripheral blood -- to expand scientists' arsenal of methods for pinpointing genes that play a role in autism. Published in the June 21 online ...

Changes in the path of brain development make human brains unique

December 6, 2011
How the human brain and human cognitive abilities evolved in less than six million years has long puzzled scientists. A new study conducted by scientists in China and Germany, and published December 6 in the online, open-access ...

Recommended for you

Our memory shifts into high gear when we think about raising our children, new study shows

December 15, 2017
Human memory has evolved so people better recall events encountered while they are thinking about raising their offspring, according to a new study conducted by researchers at Binghamton University, State University of New ...

Offbeat brain rhythms during sleep make older adults forget

December 15, 2017
Like swinging a tennis racket during a ball toss to serve an ace, slow and speedy brainwaves during deep sleep must sync up at exactly the right moment to hit the save button on new memories, according to new UC Berkeley ...

Study finds graspable objects grab attention more than images of objects do

December 15, 2017
Does having the potential to act upon an object have a unique influence on behavior and brain responses to the object? That is the question Jacqueline Snow, assistant professor of psychology at the University of Nevada, Reno, ...

Little understood cell helps mice see color

December 14, 2017
Researchers at the University of Colorado Anschutz Medical Campus have discovered that color vision in mice is far more complex than originally thought, opening the door to experiments that could potentially lead to new treatments ...

Scientists chart how brain signals connect to neurons

December 14, 2017
Scientists at Johns Hopkins have used supercomputers to create an atomic scale map that tracks how the signaling chemical glutamate binds to a neuron in the brain. The findings, say the scientists, shed light on the dynamic ...

Journaling inspires altruism through an attitude of gratitude

December 14, 2017
Gratitude does more than help maintain good health. New research at the University of Oregon finds that regularly noting feelings of gratitude in a journal leads to increased altruism.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Sigh
not rated yet Aug 23, 2012
Good work.
A big step further would be to work out how that affects the detailed neural connectivity. That would allow inferences about the differences in computations, instead of only differences in the estimated complexity of genetic interactions.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.