By Jennifer Viegas
Rats, like humans, contemplate problems by carefully weighing the costs and benefits of a situation before making decisions, according to a new study on Wistar rats, a rodent developed for research.
The study is the first to demonstrate that a non-human animal creates a desired ratio, or standard, to decide between options requiring varying levels of effort and that yield different rewards.
A person buying a new car, for example, must weigh the cost and the effort needed to make payments versus the value of the car. Rats, and likely all rodents, do something similar, only under a lot more pressure.
"In its natural habitat, rats are facing the problem that little is under their control, so they are facing various levels and forms of uncertainty all the time," said Ruud van den Bos, who led the research. "For instance, the quality and amount of food items at patches varies over time and between different patches, thus benefits are not always the same."
Van den Bos, a scientist in the Faculty of Veterinary Medicine at Utrecht University in The Netherlands, added, "The amount of energy spent to obtain these different items varies during the different foraging sessions, as sometimes it's cold, sometimes it's hot, sometimes it rains, sometimes sudden obstacles are present after heavy storms, etc."
Van den Bos and his team attempted to duplicate such challenges by manipulating barriers in a T-shaped maze that rats explored. Rats entered at the bottom of the "T," which connected two arms.
At the end of each arm was a chamber filled with treats. One side had a low reward -- one sugar pellet -- while the other side had three to five sugar pellets.
Rats that wanted the higher rewards had to climb steep barriers. It would be like placing a person's favorite dessert behind a Marines-type training wall that would have to be scaled before the individual could nosh. The researchers varied the size of the barrier and the amount of reward on that side to see how the rodents would react.
At first the rats went for the easy pickings, but when they determined more sweets were available on the other side of the maze, they exerted additional effort, but only after a certain point. When the pain yielded too little gain, they stuck with the tiny treat.
Findings have been accepted for publication in the journal Behavioral Brain Research.
The researchers also noted that rats seem to behave according to an internal constant standard, a relative ratio for each situation by which choices are measured. This is comparable to how a car purchaser may enter a dealership with a budget in mind. Since this standard varies depending on the situation, it is possibly part inherent and part created by individuals.
John Salamone, professor and head of Behavioral Neuroscience at the University of Connecticut, developed the T-maze for previous studies. He also recently authored a paper in Current Psychiatry Reviews that determined problems in the brain associated with effort-related processes, such as how much energy an individual will put out to obtain a reward, could be linked to depression.
This suggests rats get depressed too. Salamone's own research indicates interference with dopamine, a neurotransmitter chemical in the brain, may make individuals less likely to work for rewards and biased toward low-effort alternatives.
"Exertion of effort and energy and energy-related decision-making are fundamental for survival, in humans and other animals, and I am very happy that more and more people are getting involved in this sort of research," said Salamone, who added the new work as "an excellent piece of research."