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.

If the synapses are thought of as the chips in a computer, then brainpower is shaped by the sophistication of each chip, as well as by their numbers. “From the evolutionary perspective, the big brains of vertebrates not only have more synapses and neurons, but each of these synapses is more powerful  vertebrates have big Internets with big computers and invertebrates have small Internets with small computers,” Dr. Grant said.

He included yeast cells in his cross-species survey and found that they contain many proteins equivalent to those in human synapses, even though yeast is a single-celled microbe with no nervous system. The yeast proteins, used for sensing changes in the environment, suggest that the origin of the nervous system, or at least of synapses, began in this way.

The computing capabilities of the human brain may lie not so much in its neuronal network as in the complex calculations that its synapses perform, Dr. Grant said. Vertebrate synapses have about 1,000 different proteins, assembled into 13 molecular machines, one of which is built from 183 different proteins.

These synapses are not standard throughout the brain, Dr. Grant’s group has found; each region uses different combinations of the 1,000 proteins to fashion its own custom-made synapses.