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May 24, 2003

Electric conversations

From: The Globe and Mail, Canada - May 24, 2003

Researchers have figured out how a small fish uses electricity to navigate and communicate in the murky Amazon River. ANNE McILROY reports


The fish in Len Maler's lab like doing everything in the dark: hunting, swimming, finding mates. They can't see or hear, but they don't need to. Their long, thin tails generate electrical signals and their bodies are covered with specialized receptors that act like AM/FM radios.

In their natural habitat in South America, they make sense of the murky world at the bottom of the Amazon River by constantly analyzing how the electricity they generate reacts with the environment. The fish, known as Apternotus leptorhynchus, have evolved an electrical navigation and communication system that makes man-made radar seem primitive by comparison.

It is almost like a new sense -- a combination of hearing and sight, says Dr. Maler, a University of Ottawa neuroscientist. He has been studying Apternotus leptorhynchus, one of hundreds of species of electric fish, in his laboratory for 30 years.

Working with U of O physicists André Longtin, Maurice Chacron and Brent Doiron and University of Oklahoma biologist Joseph Bastian, he has pieced together how the fish use electricity to navigate muddy waters, find prey and communicate with other fish. Their latest findings were published last month in the prestigious British journal Nature.

Over the next five to 10 years, their work with the electric fish could be used to help deaf people hear and to build unmanned vehicles to explore Mars and other forbidding places.

This seems hard to believe, looking at the fish squirming unhappily as they explore a glass tank in the daylight. Dr. Maler has brought three of them up from the basement for a photo shoot, but they prefer hanging out in the insides of black plastic tubes and emerging at night.

There is nothing electrifying about their appearance. They are small -- about the length of a human hand -- and a mossy dark green. Their eyes are almost too small to see. They are known as knife fish, and their bodies are thin and rigidly straight. They have fewer fins than other fish so that the action of swimming won't interfere with their reception of electrical signals. They propel themselves with a long, feathery fin that stretches along their stomachs, and can hover in one spot like helicopters.

They aren't as electric as other sea creatures. The electric organ in their spaghetti-sized tails generates about one-thousandth of a volt. Electric eels, by comparison, can generate 600 volts.

Other fish, including sharks, have an ability to receive electrical signals that helps them find prey, but don't generate electricity themselves.

What is so fascinating about these fish is that they use electricity to communicate, through bursts of energy that sound like bird-like chirps if they are amplified and hooked up to a speaker so the scientists can hear them.

"Mature females have lower frequencies and males have high frequencies. So they can tell if it is a rival or a mate from the frequency difference," Dr. Maler says.

"They have different chirps to attract females. The females give off different signals when they are ready to lay eggs. It is a very complicated electrical dance."

It does seem more complicated than "Do you come here often?" or other human pickup lines. But using electricity to communicate and to make sense of the world may actually be simpler in biological terms than seeing and hearing, which scientists are still struggling to understand.

The mechanics are well understood, but how does the brain process the information brought in by the eyes and ears? No one is really sure. In fact, Dr. Maler was drawn to the electric fish because they provide a simpler biological model of sensory perception to study than those found in higher vertebrates, such as cats or humans.

At the same time, the fish are remarkably similar to humans, at least at a cellular level. The receptors on their skin share similarities with cells involved in human hearing. The neurons in their brains that process sensory information look exactly the same as human neurons, and use many of the same chemicals.

But it is easier to study how sensory input is handled in their brains, in part because Dr. Maler can take thin sections of fish brain and use a microscope to study neurons at work.

In fish, the brain cells that process information from the world outside get only a small fraction of their input from the sensory organs. The rest comes from within the brain -- part of a process called feedback.

It is the same for humans. Feedback is how fish make sense of the electrical signals they pick up -- how they recognize another fish from the way electricity bounces off it. It is how we make sense of what we see and hear, how we can tell the difference between a tree and a tulip.

Dr. Longtin describes this mysterious process as the language of the brain, and he is betting that it is basically the same in humans and fish.

The researchers are also interested in how the fish manage to focus in a world awash with electrical activity.

"They can communicate one on one in a soup of fish," Dr. Longtin says. There is a lot of electrical noise in the Amazon. For the fish, a lightning bolt landing in the water, for example, is the equivalent to having a rock concert in your bedroom. Yet the fish carry on with their lives.

It is this ability to tease out meaningful signals from a busy background that could lead to better cochlear implants. Known as bionic ears, these devices are implanted surgically into the ear canal of patients who aren't helped by conventional hearing aids. They bypass damaged parts of the inner ear and electronically stimulate the nerves used for hearing.

One of the problems with them is that in a crowded room, the devices can't differentiate between the sound of one voice and the sound of the crowd in the background.

If the researchers can figure out how the fish do it, they might be able to use that information to improve the performance of the implants, Dr. Longtin says.

Other researchers associated with the Jet Propulsion Laboratory at the California Institute of Technology in the United States are working on building robots or unmanned vehicles that could probe hostile environments using an electrical sensing and navigation system that mimics the one used by the fish.

Certainly, the fish have done well with their electrical adaptations. They have been extraordinarily successful since they first evolved 60 million years ago. There are hundreds of electric species in South America, Dr. Maler says. "They are the dominant fish."

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