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

August 22, 2012, University of California, Los Angeles
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

Research reveals atomic-level changes in ALS-linked protein

January 18, 2018
For the first time, researchers have described atom-by-atom changes in a family of proteins linked to amyotrophic lateral sclerosis (ALS), a group of brain disorders known as frontotemporal dementia and degenerative diseases ...

Fragile X finding shows normal neurons that interact poorly

January 18, 2018
Neurons in mice afflicted with the genetic defect that causes Fragile X syndrome (FXS) appear similar to those in healthy mice, but these neurons fail to interact normally, resulting in the long-known cognitive impairments, ...

How your brain remembers what you had for dinner last night

January 17, 2018
Confirming earlier computational models, researchers at University of California San Diego and UC San Diego School of Medicine, with colleagues in Arizona and Louisiana, report that episodic memories are encoded in the hippocampus ...

Recording a thought's fleeting trip through the brain

January 17, 2018
University of California, Berkeley neuroscientists have tracked the progress of a thought through the brain, showing clearly how the prefrontal cortex at the front of the brain coordinates activity to help us act in response ...

Midbrain 'start neurons' control whether we walk or run

January 17, 2018
Locomotion comprises the most fundamental movements we perform. It is a complex sequence from initiating the first step, to stopping when we reach our goal. At the same time, locomotion is executed at different speeds to ...

Neuroscientists suggest a model for how we gain volitional control of what we hold in our minds

January 16, 2018
Working memory is a sort of "mental sketchpad" that allows you to accomplish everyday tasks such as calling in your hungry family's takeout order and finding the bathroom you were just told "will be the third door on the ...

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.