(photo credit: Nutritional Neuroscience)
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
recently in the advance online edition of Neuron, these genes’
identification could improve understanding of human brain diseases like
autism and schizophrenia, as well as learning disorders and addictions.
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
Human Genetics 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 brain tissue,
Geschwind and his colleagues applied next-generation sequencing and
other modern methods to study gene activity in humans, chimpanzees and
rhesus macaques, a common ancestor for both chimpanzee and humans that
allowed the researchers to see where changes emerged between humans and
chimpanzees. They zeroed in on three brain regions – 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
“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.
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.
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.
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.”
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.
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 human brain.”
UCLA team’s next step will be to expand their comparative search to 10
or more regions of the human, chimpanzee and maque brains.This article was first published at www.newswise.com