How complex are your synapses?

New research suggests that not all synaptic connections are the same:

Evolution’s recipe for making a brain more complex has long seemed simple enough. Just increase the number of nerve cells, or neurons, and the interconnections between them. A human brain, for instance, is three times the volume of a chimpanzee’s.

A whole new dimension of evolutionary complexity has now emerged from a cross-species study led by Dr. Seth Grant at the Sanger Institute in England.

Dr. Grant looked at the interconnections between neurons, known as synapses, which until now have been regarded as a standard feature of neurons.

But in fact the synapses get considerably more complex going up the evolutionary scale, Dr. Grant and colleagues reported online Sunday in Nature Neuroscience. In worms and flies, the synapses mediate simple forms of learning, but in higher animals they are built from a much richer array of protein components and conduct complex learning and pattern recognition, Dr. Grant said.

The finding may open a new window into how the brain operates. “One of the biggest questions in neuroscience is to answer what are the design principles by which the human brain is constructed, and this is one of those principles,” Dr. Grant said.

Perceiving ‘optical’ illusions

The NY Times reports on the perception of so-called optical illusions:

Staring at a pattern meant to evoke an optical illusion is usually an act of idle curiosity, akin to palm reading or astrology. The dot disappears, or it doesn’t. The silhouette of the dancer spins clockwise or counterclockwise. The three-dimensional face materializes or not, and the explanation always seems to have something to do with the eye or creativity or even personality.

That’s the usual cue to nod and feign renewed absorption in the pattern.

In fact, scientists have investigated such illusions for hundreds of years, looking for clues to how the brain constructs a seamless whole from the bouncing kaleidoscope of light coming through the eyes. Brain researchers today call the illusions perceptual, not optical, because the entire visual system is involved, and their theories about what is occurring can sound as exotic as anyone’s.

In the current issue of the journal Cognitive Science, researchers at the California Institute of Technology and the University of Sussex argue that the brain’s adaptive ability to see into the near future creates many common illusions.

“It takes time for the brain to process visual information, so it has to anticipate the future to perceive the present,” said Mark Changizi, the lead author of the paper, who is now at Rensselaer Polytechnic Institute. “One common functional mechanism can explain many of these seemingly unrelated illusions.” His co-authors were Andrew Hsieh, Romi Nijhawan, Ryota Kanai and Shinsuke Shimojo.