Some electric fish, like great orators, pause for effect

Mormyrids know how to create that shocking tension while communicating with fellow fish

Michelle Vincent

Want to be a better communicator? You could take a few tips from electric fish.

Most of us know of the pause for emphasis used in speeches. Not just good orators and rabble-rousing politicians use it. We do, too, in everyday conversation, without realizing it.

Bruce Carlson, from the University of Saint Louis, and Tsunehiko Kohashi, now at Nagoya University in Japan, had seen research suggesting that the pauses of persuasive speakers tend to come just before a big chunk of information.

But why? Do the pauses help prepare the listeners for more important information? If so, is this something we just picked up in the course of evolution? Or do our brains equate a short pause with “important information ahead”?

To learn more, the researchers took to the aquarium to study mormyrids, a variety of freshwater fish that map their world using a weak electric field to find their way through muddy waters.

Also known as freshwater elephantfish, mormyrids produce electric signals and use them to check out the world around, locate prey and communicate with other mormyrids.

Shocking language

The researchers hoped the frequency of the discharges and patterns in sending and receiving the signals would indicate something about how the fish use them to communicate, which in turn could clue us in to the mechanics of human communication.

Since mormyrids use the discharges to explore their environment and also to communicate, they broadcast electric discharges pretty much all the time. But when the fish were in pairs, the frequency of signals was greater and pattern different from when they were housed alone. This gave the first clue that the fish were using the electric discharge for social behavior.

The researchers also noticed that after a pause the fish often produced high frequency bursts of electric signals. Intrigued, they experimented by inserting artificial pauses in the communication between two fish, in effect tampering with it, and discovered that the ‘listener’ fish increased their own rates of electric discharge after the inserted pauses. This suggested the pauses held some meaning for the fish.

They then turned their attention to the brains of the signal-receiving fish. Turns out mormyrid brains have a specific sensory pathway for receiving the signals of neighboring fish.

The team hoped there would be evidence in the neurons of these fish that would explain their behavior. They measured the effects of receiving electric signals over time, hoping to see evidence that the fish’s brain cells were indeed paying extra attention following their neighbor’s pause. Specifically, they measured the neurological response after a long series of electric discharges without a break versus the response to discharges separated by pauses.

They found that by allowing neurons a brief rest, the neurons were better equipped to process the bit of information that came next.

“Sure enough,” says Carlson, “if you don’t allow enough time since the previous stimulus was delivered, then the response will be weaker… and it took about a second or two for the system to recover.”

Those significant pauses

After collecting data for a year, the researchers were on to something and submitted their findings for review.

“We place wires in the water and hook those wires up to an amplifier connected to a speaker,” said Carlson, describing the process used in the wild. “This converts the electrical pulses into sound pulses (in the same way computer speakers, ear buds, etc. convert electrical waves into sound waves).”

One piece that was added after the initial review was more data proving that the signals weren’t just noise. While the ‘listener’ fish’s brain might be better prepared to receive and process information after a pause, was there any evidence that the ‘speaker’ fish was actually taking advantage of this?

While the electrical impulses underwater are not sound, they can be converted to sound so the researchers could actually hear the fish communicating. “Basically,” says Carlson, “we place wires in the water and hook those wires up to an amplifier connected to a speaker, and this converts the electrical pulses into sound pulses”, like computer speakers and ear buds do.

There are three types of electric signals, called burst displays, that previous researchers had already noted as important in mormyrid-speak: rasps, scallops and accelerations. Carlson and his team found that not only did the paired fish have more pauses in electric discharge than solitary fish, the chance of a burst display was much higher immediately after a pause.

“We found that they tended to produce other communication signals right after using these pauses. That helped solidify a link to what we know about human language and the fact that we tend to use highly informative words right after a pause,” Carlson said. “It seems like these fish are doing something analogous.” So mormyrids do pause before making a big announcement, just like humans.

The research showed these communication patterns occurred in both the environment and on a cellular level. There are obvious implications for those who study human communication, and other species might offer more clues. They may even show that this is phenomenon is widespread in animals.

Carlson’s bet is that frogs might make the next big headline.

“A really interesting follow-up for people studying other systems is whether this exact same mechanism is happening in their system, whether it’s song birds singing or frogs croaking or crickets chirping, whether they are seeing the same phenomenon and whether the same mechanism can explain it,” he said.

Humans are programmed to pay more attention to new things. Over time, both electric fish and humans have taken advantage of that fact to tailor our communication to our listeners. Instead of droning on, one sentence flowing into the next, we have learned to take advantage of our listeners’ brain wiring. By giving the brain a short rest, we unconsciously prompt our audience to take more notice immediately afterward.

So, the next time you want to have a crowd hanging on your every word, think of how a mormyrid would do it.

The original report appeared in Cell

Michelle Vincent is a freelance writer whose early scientific influences include “Mr. Wizard,” Laika the Russian space dog, and “The Twilight Zone.” A native Midwesterner adapting to Southern life, she enjoys traveling with her husband, playing with her two rescue dogs, and air conditioning.

Related article

Getting zapped for science