/By Ilan Shavit/
New research at the Weizmann Institute shows that mice that have been raised in a stimulus-rich environment have less complexity in their social interactions than those growing up in more Spartan conditions.
The detailed research appears Tuesday in the scientific journal eLife, and it was a collaborative study between two very different groups in the Institute’s Neurobiology Department. Professor Alon Chen deals with molecules in the nervous system that affect behaviour, while Dr. Elad Schneidman is a theoretician who works on the nature of collective behaviour. The experimental system for the research was created by the team, which included Drs. Yair Shemesh, Oren Forkosh and Yehezkel Sztainberg, and Tamar Shlapobersky.
The system created was a large “arena” with points of interest – sleeping nests, stations for food and games, and more. The team tracked mice over four nights running, recording everything under ultraviolet lighting so as not to disturb the mice’s normal nocturnal routines.
Their findings are based on two innovative developments: first is an automated system that continuously tracks groups of mice living in semi-natural conditions; and the second is a mathematical framework for analyzing the data.
A theoretical calculation based on each mouse’s individual likes and fears yielded 4, 000 possible arrangements, but only around half of these actually occurred.
The scientists employed a mathematical model from statistical physics called the “maximum entropy model, ” which is applied in many different types of research to analyze data on relationships in complex systems with minimal reliance on initial assumptions.
Here they analyzed the importance of relationships of different orders – from the first order in which a single mouse acts independently of the others, through the second order of paired relationships, and on to third- and fourth-order relationships.
Mouse social activity seems, on the surface, to be pair-based: chasing, approaching, fighting, etc.
Yet, surprisingly, the team found that third-order relationships carried around a third of the weight of the group behavior. The scientists suggest that complex social structures evolved for survival.
The scientists then asked how the environment in which the mice are raised affects the social structure?
Analysis with the mathematical model revealed a significant difference: Mice that had grown up in the complex environment engaged in less of the appropriate social activity, and their group behavior was much more dominated by pair relationships than triple ones.
In contrast, not only did the second, standard groups exhibit more complexity in their social structure, they even advanced in “sociability” over the course of the experiment, while the first groups did not.
The difference, say the scientists, might arise because a rich society enables more individualism and reduces the need for dependence on the group.
The results of the study to date offer many lines of thought for subsequent research.
Mickey’s Photo courtesy : Wikipedia