Living in a group can be a hard thing to navigate, especially as an individual’s short-term interest can conflict strongly with the group’s long-term interests. A new paper looks into how mice juggle costs and benefits in social settings, with implications for other animals and humans as well.
People have learned to live together in huge communities, and a big part of that is solving conflicts through compromise and by following rules, instead of making justice with one’s fists. The sheer scale and complexity of the frameworks of rules we use to guide these resolutions, as well as our heavy reliance on cooperation, sets us apart from other animals.
Still, this also raises a question. How did this web of rules and cooperation evolve, and can other animals set up new social rules to help guide their interaction? A new study from the Center for Cognition and Sociality, part of the Institute for Basic Science (IBS), shows that lab mice can establish and then follow rules that are equitable (provide equal rewards in the long-term) even if they have to exercise patience and tolerance in the short-term. The findings provide a glimpse into how humans and other animals weigh costs and benefits in social interactions.
I don’t make the rules I just work here
Competition can be a powerful tool to getting what you want and need. But it’s also a very risky, one-against-all strategy, which comes with great costs both of time and of energy. With that in mind, humans generally adopt rules to guide how people with conflicting interests solve their differences without having to resort to aggression. The ‘first-come, first-served’ approach, or territorial ownership, are examples of such rules that, in the long-term, maximize the mutual benefit of everybody involved.
Other species also follow such rules. Some species of social spiders, the team notes, will back away when trespassing on someone else’s territory and will look for an unoccupied place. Rodents, however, are known to be impulse-driven, especially when food is concerned. A mouse would rather eat a small amount of food now than wait for a large serving later. Chow, after all, is a matter of survival.
However, the IBS researchers were curious to see how well-fed mice would behave when presented with a less immediate and necessary reward — could they learn to adapt to new social rules to maximize the rewards for all involved?
In lieu of food, the team used headsets that could produce a wireless electrical brain stimulation (WBS) in the medial forebrain bundle, the brain’s reward circuitry. The mice would feel this as a very powerful (yet nonaddictive) sense of pleasure, which they tend to prefer even over mating, as previous work revealed.
The mice were then trained using a specially designed box. It had a starting area in the center, and two reward zones to its left and right. The animals learned to start the round by entering the central area, and then follow a blue light indicating one of the reward zones. The light was randomly allocated and indicated where a mouse had to go to receive a five-second WBS pleasure-burst.
For the experiment, the team first placed two trained mice in the same box, setting them up for a winner-takes-all scenario. The mice had to further learn that the round only started when both entered the start zone together. Moreover, they had to figure out that only the first mouse to enter would receive the WBS — as soon as the second one entered the same zone, the signal was interrupted.
Over time, the researchers report, mice developed a “social rule” through which to split up the box. One mouse would only go for the pleasure doses on the left zone, while the other would only go for those on the right. Out of the 38 mice tested in this step, 23 (60%) observed the rule and waited for their turn. Those that respected the rule went through more rounds during the experiment than their peers, thus receiving more reward time overall. In other words, despite the initial effort of obeying the rules, teams of cooperating mice got more reward for each member than those who didn’t work together.
“Violating the rule is not a problem in the short term, but it is not sustainable in the long-term,” says Professor Shin Hee-Sup, corresponding author of the study. “Mice that respect the social rule learn how to play to their mutual advantage.”
However, he admits that the mice were still tempted to cheat the system and get some extra reward out of the situation. “From time to time,” even the most cooperating mice would, after waiting for a few seconds so as not to disrupt the other mouse’s WBS hit, “try their luck by going to the opponent’s territory,” Hee-Sup explains. Here is where another rule underpinning social cooperation comes into play.
“Another rule is tolerance. If a mouse violates the rule, the other mouse has the choice of retaliate immediately, or tolerate and keep on observing the rule. Tit for tat brings a disruption of the system, while tolerance to partner’s mistakes allows the system to continue, and as a result both mice receive a long-term benefit,” explains the professor. “This is called Bourgeois strategy in psychology. It limits aggression and is better for the long-term.”
Overall, rule observance increased over time during the test. This happened independently of the mice’s body weight or learning ability. To prevent habit (such as a mouse forming a preference for one side of the box) from biasing the results, the authors also swapped members between the teams to couple rats that had previously gone on the same side. Disoriented and confused at first, the animals quickly re-assigned territory, one going to the left and one to the right. This phenomenon is known as “rapid rule transfer,” and shows that mice are capable of adapting the same social rule to new situations.
In the future, the authors want to see if familiarity between the mice influences their tendency to observe the rules. Another interesting avenue of research would be to see if the mice keep following the rules in unfair conditions — i.e. when they’re trained to expect that the zones receive an equal amount of reward but that doesn’t happen.
The paper “Mice in social conflict show rule-observance behavior enhancing long-term benefit” has been published in the journal Nature Communications.
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