Origins of the brain: Complex synapses drove brain evolution

June 8, 2008

One of the great scientific challenges is to understand the design principles and origins of the human brain. New research has shed light on the evolutionary origins of the brain and how it evolved into the remarkably complex structure found in humans.

The research suggests that it is not size alone that gives more brain power, but that, during evolution, increasingly sophisticated molecular processing of nerve impulses allowed development of animals with more complex behaviours.

The study shows that two waves of increased sophistication in the structure of nerve junctions could have been the force that allowed complex brains - including our own - to evolve. The big building blocks evolved before big brains.

Current thinking suggests that the protein components of nerve connections - called synapses - are similar in most animals from humble worms to humans and that it is increase in the number of synapses in larger animals that allows more sophisticated thought.

"Our simple view that 'more nerves' is sufficient to explain 'more brain power' is simply not supported by our study," explained Professor Seth Grant, Head of the Genes to Cognition Programme at the Wellcome Trust Sanger Institute and leader of the project. "Although many studies have looked at the number of neurons, none has looked at the molecular composition of neuron connections. We found dramatic differences in the numbers of proteins in the neuron connections between different species".

"We studied around 600 proteins that are found in mammalian synapses and were surprised to find that only 50 percent of these are also found in invertebrate synapses, and about 25 percent are in single-cell animals, which obviously don't have a brain."

Synapses are the junctions between nerves where electrical signals from one cell are transferred through a series of biochemical switches to the next. However, synapses are not simply soldered joints, but mini-processors that give the nervous systems the property of learning and memory.

Remarkably, the study shows that some of the proteins involved in synapse signalling and learning and memory are found in yeast, where they act to respond to signals from their environment, such as stress due to limited food or temperature change.

"The set of proteins found in single-cell animals represents the ancient or 'protosynapse' involved with simple behaviours," continues Professor Grant. "This set of proteins was embellished by addition of new proteins with the evolution of invertebrates and vertebrates and this has contributed to the more complex behaviours of these animals.

"The number and complexity of proteins in the synapse first exploded when muticellular animals emerged, some billion years ago. A second wave occurred with the appearance of vertebrates, perhaps 500 million years ago"

One of the team's major achievements was to isolate, for the first time, the synapse proteins from brains of flies, which confirmed that invertebrates have a simpler set of proteins than vertebrates.

Most important for understanding of human thought, they found the expansion in proteins that occurred in vertebrates provided a pool of proteins that were used for making different parts of the brain into the specialised regions such as cortex, cerebellum and spinal cord.

Since the evolution of molecularly complex, 'big' synapses occurred before the emergence of large brains, it may be that these molecular evolutionary events were necessary to allow evolution of big brains found in humans, primates and other vertebrates.

Behavioural studies in animals in which mutations have disrupted synapse genes support the conclusion that the synapse proteins that evolved in vertebrates give rise to a wider range of behaviours including those involved with the highest mental functions. For example, one of the 'vertebrate innovation' genes called SAP102 is necessary for a mouse to use the correct learning strategy when solving mazes, and when this gene is defective in human it results in a form of mental disability.

"The molecular evolution of the synapse is like the evolution of computer chips - the increasing complexity has given them more power and those animals with the most powerful chips can do the most," continues Professor Grant.

Simple invertebrate species have a set of simple forms of learning powered by molecularly simple synapses, and the complex mammalian species show a wider range of types of learning powered by molecularly very complex synapses.

"It is amazing how a process of Darwinian evolution by tinkering and improvement has generated, from a collection of sensory proteins in yeast, the complex synapse of mammals associated with learning and cognition," said Dr Richard Emes, Lecturer in Bioinformatics at Keele University, and joint first author on the paper.

The new findings will be important in understanding normal functioning of the human brain and will be directly relevant to disease studies. Professor Grant's team have identified recently evolved genes involved in impaired human cognition and modelled those deficits in the mouse.

"This work leads to a new and simple model for understanding the origins and diversity of brains and behaviour in all species" says Professor Grant, adding that "we are one step closer to understanding the logic behind the complexity of human brains"

Citation: Emes RD, Pocklington AJ, Anderson CNG, Bayes A, Collins MO, Vickers CA, Croning MDR, Malik BR, Choudhary JS, Armstrong JD and Grant SGN (2008), Evolutionary expansion and anatomical specialization of synapse proteome complexity. Nature Neuroscience published online Sunday 8 June 2008 ; dx.doi.org/10.1038/nn.2135

Source: Wellcome Trust Sanger Institute

Explore further: Scientists identify key regulator of male fertility

Related Stories

Scientists identify key regulator of male fertility

September 19, 2017
When it comes to male reproductive fertility, timing is everything. Now scientists are finding new details on how disruption of this timing may contribute to male infertility or congenital illness.

Scientists are unraveling the mystery of your body's clock – and soon may be able to reset it

September 18, 2017
For people who don't get sleepy until 2 a.m., the buzz of an alarm clock can feel mighty oppressive.

Laser device placed on the heart identifies insufficient oxygenation better than other measures

September 20, 2017
A new device can assess in real time whether the body's tissues are receiving enough oxygen and, placed on the heart, can predict cardiac arrest in critically ill heart patients, report researchers at Boston Children's Hospital ...

Study associates schizophrenia with defective processing of messenger RNA in cells

September 6, 2017
Schizophrenia affects approximately 1 percent of the world's population and is the main cause of psychiatric incapacitation. Despite its high prevalence and the severity of its symptoms, little is known about the biochemical ...

Turtles may hold the key to protecting human hearts after heart attack

August 29, 2017
In humans, going just minutes without oxygen—such as during a heart attack or stroke—can cause devastating damage to the heart. Conversely, freshwater turtles hibernate for months at the bottom of frozen lakes and awake ...

Manipulating a single gene defines a new pathway to anxiety

August 24, 2017
Removing a single gene from the brains of mice and zebrafish causes these animals to become more anxious than normal. Researchers from University of Utah Health show that eliminating the gene encoding Lef1 disrupts the development ...

Recommended for you

Image ordering often based on factors other than patient need: study

September 25, 2017
Do you really need that MRI?

Bone marrow concentrate improves joint transplants

September 25, 2017
Biologic joint restoration using donor tissue instead of traditional metal and plastic may be an option for active patients with joint defects. Although recovery from a biologic joint repair is typically longer than traditional ...

How ketogenic diets curb inflammation

September 25, 2017
Ketogenic diets – extreme low-carbohydrate, high-fat regimens that have long been known to benefit epilepsy and other neurological illnesses – may work by lowering inflammation in the brain, according to new research ...

Researchers develop treatment to reduce rate of cleft palate relapse complication

September 22, 2017
Young people with cleft palate may one day face fewer painful surgeries and spend less time undergoing uncomfortable orthodontic treatments thanks to a new therapy developed by researchers from the UCLA School of Dentistry. ...

Exosomes are the missing link to insulin resistance in diabetes

September 21, 2017
Chronic tissue inflammation resulting from obesity is an underlying cause of insulin resistance and type 2 diabetes. But the mechanism by which this occurs has remained cloaked, until now.

Thousands of new microbial communities identified in human body

September 20, 2017
A new study of the human microbiome—the trillions of microbial organisms that live on and within our bodies—has analyzed thousands of new measurements of microbial communities from the gut, skin, mouth, and vaginal microbiome, ...

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

thales
4.7 / 5 (3) Jun 08, 2008
Now let's model it in a computer and make one. http://bluebrain....699.html
moebiex
not rated yet Jun 09, 2008
Could these novel proteins have evolved in response to the appearrance within the brain of chemicals from plants ingested as part of the animal's diet?
Mercury_01
4 / 5 (1) Jun 09, 2008
If we can now better guage an animals inteligence by studying brain chemistry, how about telling us which animals are smarter than us, so we know who to watch out for.
thales
not rated yet Jun 09, 2008
Here's a much better overview of the project to model a brain. Pretty heady stuff (no pun intended).

http://www.seedma...page=all&p=y

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.