Comment Motivation is a complicated emotion (Score 4, Insightful) 200
Behavioral experiments like this are relatively straightforward to plan and run. The hard part is to explain the result, and the reasons are not always what you'd expect on first glance, often due to confounding variables that you've inadvertently changed.
It's also worth noting that the news release throws in a quote about altruism, but the original paper's authors were careful not to go there.
For example, reading this carefully, it's clear that the rat frees its cagemate and then goes for the chocolate. It's not a binary choice between the two. Why does it do that? Perhaps it's hidden empathy/altruism circuitry. Or maybe the rat's just afraid of what its cagemate will do if it eats all the food and then the trapped rat gets out. Contrary to what most people think, domesticated rats are very much like domesticated dogs in terms of temperament... very social animals, usually with a playful temperament, but can also be very territorial and assertive. And territorial fighting usually occurs over shared, limited resources, like food. (I will say, chocolate is a good choice. Rats love chocolate. Some of our rats will eat 30 - 40 M&Ms in a half-hour experiment. Not bad for an animal weighing 300 grams.)
Maybe it is altruism or empathy. But true altruism is doing something good and expecting nothing in return, not a pain avoidance strategy.