tl;dr: Rodents will help each other get out of trouble, though they will help each other more if they are related. Social learning in rodents can require information transmission between ACC and amygdala, and the strength of synapses in mPFC dictates social status.
He wanders into the room and stops – someone else is peering at him out of a tiny plastic cage. Wandering over he must decide: should he help him out of the cage? Or let the creepy situation remain creepy, and leave them stuck in there?
Rats, it turns out, aren’t big fans of creepy situations and will actively go out of their way to help their furry compatriots escape from their cages. Not only will they help other rats escape their cages – even if they don’t know them – but if they find a bite of chocolate they’ll hand over some of that as well. [Though if you look at the data: the little bastards wait half a week before they get around to doing it.]
That’s fine but things can get a bit sinister when the rats aren’t just strangers but strangers that appear different. When they find another rat trapped in a cage that is of a different strain, the free rats would rarely attempt to let the trapped rats loose. This isn’t purely a matter of rats being different from one another, but rather of rat-features that they weren’t familiar with. When rats were housed with rats of different strains, they would help other rats of that strain out. Individuals of that outgroup had been ‘humanized’, so to speak. Yet, own-group preference wasn’t innate – if they weren’t housed with other rats of their own strain, they wouldn’t help them, either. For an example, watch this movie from the paper (which I can’t directly embed).
We already know a bit about the neuroscience of empathy and social structure in rodents. A mouse that observes a fellow mouse receiving painful shocks in a certain area of their cage will learn to avoid that area through pure social observation. However, they learn better when it is a sibling that is being shocked than when it is an unrelated rat. This learning requires a region of the brain known as the anterior cingulate cortex (ACC), though the region can be inactivated during later retrieval and recall without affecting the behavior. It also requires the amygdala, not just for learning but also for later retrieval and recall. During learning, the ACC and amygdala are connected by strong (theta) rhythms, potentially to transmit information between the areas.
Another factor guiding social behavior is social status. Status affects behavior on a range of levels, from how decisions are made to how healthy an individual is. It is pretty surprising to me that in rodents, social status can be directly changed by changing the strength of synapses in the medial prefrontal cortex (mPFC). I’ve only ever seen a broad neuromodulator like serotonin do something like that, though I would hesitate before suggesting that they two mechanisms were connected. On the other hand, mPFC is upstream of serotonergic areas so increased synaptic strength could mean increased serotonin!
Ben-Ami Bartal I, Rodgers DA, Bernardez Sarria MS, Decety J, & Mason P (2014). Pro-social behavior in rats is modulated by social experience. eLife, 3 PMID: 24424411
Ben-Ami Bartal I, Decety J, & Mason P (2011). Empathy and pro-social behavior in rats. Science (New York, N.Y.), 334 (6061), 1427-30 PMID: 22158823
Wang F, Zhu J, Zhu H, Zhang Q, Lin Z, & Hu H (2011). Bidirectional control of social hierarchy by synaptic efficacy in medial prefrontal cortex. Science (New York, N.Y.), 334 (6056), 693-7 PMID: 21960531
Jeon D, Kim S, Chetana M, Jo D, Ruley HE, Lin SY, Rabah D, Kinet JP, & Shin HS (2010). Observational fear learning involves affective pain system and Cav1.2 Ca2+ channels in ACC. Nature neuroscience, 13 (4), 482-8 PMID: 20190743