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Sea slug study shows brains rewiring themselves

Monday, October 19, 2009 – Ann Claycombe

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One of the great mysteries of the brain – whether animal or human – is its capacity to rewire itself after an injury. Even when the physical damage is permanent, brains can often re-organize their internal circuits in order to do the same old jobs in an entirely new way.

Researchers at Georgia State have just succeeded in mapping out one of these post-injury restructurings. Senior post-doctoral fellow Akira Sakurai, working with Professor Paul Katz, has shown how sea slugs rebound from having a major nerve cut, rerouting neural connections so they can swim again.

“One of the reviewers of the article pointed out the similarity to what researchers see in humans with spinal cord injuries,” Katz said, “that there is some recovery without regeneration.”

Sakurai and Katz performed their experiments on the sea slug species known as Tritonia Diomedea, which swims by bending forward and then arching backward. One of the advantages of working with Tritonia is that scientists have already charted the neural circuit that control the flipping, bending movement. And the circuit consists of only three neurons, which makes experiments relatively straightforward.

The first step in the experiment was to cut the neuron in the middle, thus breaking the circuit. Afterward, the sea slugs swam weakly or not at all.

That wasn’t the end of the story, though: after 15 hours had passed, all of the test slugs began to swim again. Their wounds hadn’t healed, so what had happened?

Through connecting slug brains up to electrodes, Sakurai and Katz found their answer: the first and last neurons were once again connected, not through the severed neuron but through a different part of the brain.

“The circuit is compensating in some way,” Katz said. “We don’t know how.”

Figuring out how a slug’s brain reorganizes itself is the next step, Katz said – as well as figuring out why some of the animals were able to do it more quickly than others.

In the long run, this research may lead to a better understanding of how brains in other species recover from injuries – and eventually, how to help them heal.

The article, titled "Functional Recovery following lesion of a central pattern generator," was a featured article in the Oct. 21 issue of the Journal of Neuroscience. The research was supported by a seed grant from the Brains and Behavior Program at Georgia State, as well as by the National Institutes of Health.