Two electric fish fill out an online dating profile. One fish’s profile reads: “I like long swims along the riverbank and Edith Wharton novels. I can’t stand ketchup.” The other fish’s profile reads: “I don’t know how I feel about ketchup because scientists switched off the part of my brain that allows me to tell the difference between signals coming from my body and signals coming from the outside world. I have no idea who I am or even if I’m a ‘who’ an ‘I’ or an ‘am’.” Some version of this scenario may be happening to elephantnose electric fish when scientists attempt to test the brain’s ability to differentiate between the self and other. They do this by shutting off the fish’s brain mechanism that generates future predictions about interactions with the world based on past interactions. A new study out today in Neuron shows that when this prediction mechanism is switched off, the fish’s brain can no longer distinguish between its internal signals and external input, effectively making it blind to the world outside. The researchers who conducted the study suspect this mechanism in fish brains is similar to a mechanism in all animals, including humans.
Prediction and Self.
The brain is constantly taking sensory snapshots to create a detailed and dynamic impression of the world around us as we interact with it. It’s an overwhelming amount of information for the brain to process.
“For all animals, at least all animals that move, there’s this basic problem that the sensory systems in the brain have to distinguish what patterns of sensory input are due to behaviorally relevant things out in the world,” says Nathaniel Sawtell, a neuroscientist at Columbia University’s Zuckerman Institute and senior author of the study.
Neuroscientists theorize that dealing with all this information is made possible via something called a negative image. A negative image is an image made up of past experiences (snapshots) of an organism interacting with its environment. The brain projects these snapshots into the future, as a prediction about future interactions with the world.
The brain can then ignore or cancel out new stimuli that track with the prediction so it can focus on unpredictable and potentially threatening stimuli such as predators or prey. This might also mean an organism’s current impression of the world is a collage of real-time, unpredictable sensory experiences, as well as the brain’s generated predictions. The researchers wanted to test this hypothesis and chose as their ideal candidate an elephantnose electric fish that can sense and interact with the world by generating and detecting an electrical field.
Testing the predictions.
“If we could easily study [negative images] in humans, we would do that,” says Sawtell. “But we do it in the fish because that’s the place where we can really get our hands on these things.” Sawtell and his colleagues isolated this negative image/predictive mechanism in a particular class of neurons in the electrosensory lobe (ELL) of elephantnose electric fish. When the mechanism was surgically switched off, the fish were unable to distinguish between signals they were generating and signals generated by prey in the environment. “In the lab, we can study this characteristic as a model for how other animals, including humans, sense their surroundings,”says Sawtell via press release.
Studying us versus them.
Neuroscientists are often circumspect when discussing their findings for these types of studies. They quite legitimately can’t ask the fish what’s going on inside its head. They have to rely on observing the animal’s brain activity and behavior as the basis for making claims about how other animal and human brains might work, and how this might impact sensory perception, experience, self versus other. But they also don’t want to anthropomorphize by attributing human characteristics to non-humans. This presents a challenge when testing animal brains to better understand how human brains work. But maybe now it doesn’t have to. Switch off the part of the brain that lets us distinguish ourselves from fish, and this problem might simply go away. Though it may also tailspin you into an identity crisis.