“Normally, when you think of how neurons talk to each other, you have one neuron that makes a selective set of connections to other neurons. That’s not how these cells work,” said Jennifer Li, Ph.D. ’13, another lead author and also a former fellow at the Rowland Institute. “When these cells fire, almost all other cells in your brain are listening. They are not a way to communicate narrowly from one information channel to another. They send a signal that gets broadcast to your entire brain.”
This makes sense, Li said, because this type of system is exactly what’s needed to set a global brain state. It’s also interesting that the brain naturally sets a timer for this, she added.
When a zebrafish’s priority is to hunt, the switching mechanism leaps into action, making the zebrafish not only a more motivated but a more effective hunter, because cells in the brain that amplify motor functions related to hunting — like making highly precise turns —are also heightened. This state lasts about 5 to 8 minutes and, in a chart, looks like a triangle. “It shoots up to a really high level and slowly winds down, like the discharging of a battery,” Robson said.
In the opposing state, when the signal fully discharges, skills and desires related to hunting are suppressed and the animal seems more interested in exploring its environment and covering longer distances. In this state, even if the zebrafish is hungry and presented with prey, it is routinely inattentive to it, demonstrating a different set of internal priorities. In fact, when it tries to hunt in the exploratory state, the researchers report the fish is more likely to fail.
The researchers hypothesize that the zebrafish makes this switch because it is balancing two competing priorities: eating and not being eaten. The findings call into play the questions of how long a focused state can be maintained, and even controlled.
“You don’t want an animal to be perfectly focused for an infinite amount of time, because that isn’t how an animal has to survive in the world,” Li said. “They have to switch out of that state so that they can balance all of their other objectives in life.”