At Howard Hughes Medical Institute’s Janelia Research Campus, scientists claim to have shown that the brain is able to temporarily disconnect past experiences from decision-making brain regions. The consequence of this disconnection is that decision-forming lessons are abandoned, leading to random behavior.
The researchers consider that, in some instances, random behavior might actually be preferable to experience-informed decision making. For instance, an animal might have the best chance of avoiding predation if it moves unpredictably.
Some scientists have wondered, therefore, if the brain has an inbuilt method of switching these experiences off, to produce random behavior.
The Janelia team decided to investigate this, despite some criticism from other researchers. “They argue that it’s inefficient, and that it would be at odds with what some people call one of the most central operating principles of the brain – to use our past experience and knowledge to optimize behavioral choices,” explains lab head Alla Karpova.
Of the team’s research, Karpova says they attempted “to create a setting that would push the need to create behavioral variability and unpredictability to its extreme.”
To create this environment, the researchers placed rats in a competitive setting where a computer determined which of two available holes in the habitat would produce a sweet treat for the rats.
What is more, the computer was able to analyze the rats’ behavior, predict their future behaviors and then vary its actions accordingly. A “sophistication” variable in the computer’s software was controlled by the researchers.
“We thought if we came up with very sophisticated competitors, then the animals would eventually be unable to figure out how to outcompete them, and be forced to either give up or switch into this [random] mode, if such a mode exists.”
The team’s prediction was correct. When the computer was operating on a low sophistication setting, the rats would make strategic choices based on the outcomes of previous trials.
But when the researchers cranked up the machine’s sophistication powers, allowing it to make strong predictions, the rats disregarded past experience and – in their search for the sugary prize – made seemingly random selections.
The next step for the researchers was to investigate exactly how the rat brains initiate this random behavior. The team wondered if the anterior cingulate cortex of the brain might be responsible – as it is this brain region where the “internal model” of our world is most likely encoded.
By manipulating a stress hormone – norepinephrine – in the animals’ anterior cingulate cortex, the researchers found that they could indeed switch the rats’ behavior between random and strategic modes.
When the hormone was increased, the random behavior was activated, and when the hormone was suppressed, the rats entered random mode.
However, Karpova and colleagues noticed that some rats continued to behave randomly, even when there was no strategic advantage to their randomness:
“If all they’ve experienced is this really sophisticated competitor for several sessions that thwarts their attempts at strategic, model-based counter-prediction, they go into this [random mode], and they can get stuck in it for quite some time after that competitor is gone.”
Karpova suggests this behavior is a kind of “learned helplessness,” similar to when decision making is impaired after a person encounters an experience in which they are unable to control their environment.
By suppressing the release of norepinephrine in the anterior cingulate cortex, though, the team was able to release the rats from this “stuck” behavior. “We think this might shed light on what has gone wrong in conditions such as learned helplessness, and possibly how we can help alleviate them,” Karpova says.
Now that the researchers – who publish their results in the journal Cell – have identified a mechanism that switches the brain between random and strategic behaviors, they are interested in exploring how these behaviors are controlled in more everyday settings.
“We normally try to use all of our knowledge to think strategically, but sometimes we still need to explore,” Karpova suggests.