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Electric fish helps scientists understand how the brain filters out internal stimuli

By
Brooks Hays
The elephant-nose fish's brain hosts a system of neurons responsible for creating a negative image of the fish's internal noise, allowing it to filter out useless internal information and focus on external stimuli. Photo by Sawtell lab
The elephant-nose fish's brain hosts a system of neurons responsible for creating a "negative image" of the fish's internal noise, allowing it to filter out useless internal information and focus on external stimuli. Photo by Sawtell lab

July 11 (UPI) -- Without the brain's noise-cancellation capabilities, life would be too disorienting. The ability to filter out internal stimuli is essential to our ability to process the world around us.

Scientists at Columbia University have identified the neurological origins of this ability inside the tiny brains of electric fish.

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"At its most fundamental, the brain's purpose is to create an accurate and stable representation of the world around us, and we've long hypothesized that this noise-cancellation mechanism played a part in that," Nathaniel Sawtell, a postdoctoral researcher at Columbia, said in a news release. "With today's study, we offer direct evidence that this mechanism is essential to improve and enhance the brain's ability to sense its surroundings."

The latest study, published this week in the journal Neuron, builds on earlier work by Sawtell, which showed how animals filter out predictable sensory data generated within. Previous experiments by Sawtell and his colleagues suggested the brain forms a "negative image" of internal signals.

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"This acts as a kind of subtraction mechanism, allowing animal to focus on behaviorally important, signals coming in from the outside world," said Sawtell, who is also an associate professor of neuroscience.

In their followup study, researchers wanted to better understand how the negative image impacts an organism's ability to sense the outside world. To find out, researchers used the elephant-nose fish as their subject. The species uses electricity to sense its surroundings.

In the lab, scientists measured the electrical signals generated by the neurons responsible for creating the negative image. Tests showed the neurons failed to react to external stimuli until after the negative image was formed.

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When researchers silenced the neurons responsible for creating the negative image, the fish became disoriented.

"The fish could no longer distinguish between electrical signals generated by their environment and the signals generated by their own actions," said Sawtell. "This means they were essentially blind to their surroundings at the most basic level."

In future studies, scientists draw connections between the noise-cancelling capabilities of mice and fish brains and the filtering capabilities of the human brain. Future research could also help scientists understand how the human brain's noise-cancelling system can go awry.

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"One example of this is tinnitus, which causes a ringing of the ears and which may begin in the dorsal cochlear nucleus -- a brain region we study in mice and that has striking similarities to the human equivalent in a brain region called the cerebellum," said Sawtell. "What we learn in electric fish is likely to be relevant for understanding how the human brain distinguishes self from other."

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