Laughing It Up

320px-Fancy_rat_blazeIn skimming journals to find articles to discuss on this blog, I frequently see studies that, based on title alone, seem a bit unbelievable. Recently I came across the most unbelievable-sounding one so far: Laughing Rats are Optimistic. Rats can be optimistic? How would you even measure that? Wait – rats can laugh?


To begin with the last question, yes, actually, they can. Rats make certain Ultrasonic Vocalizations (USVs) – sounds that are too high-pitched for humans to hear – that seem to be analogous to human laughter. For example, rats emit these USVs in response to pleasant stimuli, and when playing or being tickled. Additionally, stimulating the reward circuit of the brain increases the rates of USVs in rats.

If these USVs are truly analogous to human laughter, then they similarly serve as an indicator of a positive affective state in rats. Put more plainly, these USVs are a sign that a rat is happy. And this could be good information to know because, in humans, emotional state can greatly affect cognitive processes like decision-making. What if the same is true for animals?

Rygula et al. (2012) wanted to know if rats in a positive affective state are also more optimistic. We know how to tell us if a rat is in a positive affective state (USVs), and also how to put a rat in a positive affective state (tickling). But how can we tell if a rat is optimistic?

The researchers began by teaching the rats a very simple task. If a particular (“positive”) tone was played, the rat could push one lever (the “positive” lever) to receive a reward. If a different (“negative”) tone was played, the rat had to push another lever (the “negative” lever) to avoid a punishment (a small shock to the foot). The rats easily learned these associations, and were able to discriminate between the two tones.

WT_and_TK_rat_photoBut how would the rat respond if the researchers played a tone in between the positive and negative tones? An optimistic rat would expect the tone to indicate a reward, so it would be more likely to push the positive lever. A pessimistic rat, on the other hand, would expect the tone to indicate a punishment, so it would be more likely to push the negative lever.

After training the rats on the initial task, Rygula et al. tested the rats on the intermediate tone in two different sessions. In one session, the rats were tickled before being tested; in the other session, they were merely held before being tested.

Overall, the rats didn’t push the positive lever significantly more often after being tickled than after being held. However, when they took a closer look at the data, the researchers found individual differences in how much the rats laughed in response to the tickling; some rats laughed a lot, while others barely laughed at all. The researchers thus divided the rats into two groups (those that laughed when tickled and those that did not) and analyzed the data again. They found that the rats that laughed when tickled did press the positive lever significantly more often after being tickled than after being held. There was no significant difference found for the rats that didn’t laugh when tickled.

These results indicate that laughing rats are indeed more optimistic, and more generally, that affect can influence cognitive processes like decision-making in rats. This study also serves as an important reminder to be aware of individual differences in subjects; although it had been previously shown that tickling could elicit USVs, it clearly didn’t do so for all rats (or at least not to the same degree). By just combining the results of all the rats, the significant relationship between USVs and optimism was obscured.


Here’s a short video about detecting rat laughter (and how to tickle a rat). In addition to rats, non-human primates and dogs also laugh. In fact, it’s been found that playing recordings of dog laughter for shelter dogs actually decreases their stress behaviors!


Source Cited:

Rygula, Rafal, Helena Pluta, and Piotr Popik. “Laughing rats are optimistic.” PloS one 7.12 (2012): e51959.

Mission Accomplished

Have you ever noticed, upon achieving a goal, the rewarding sense of accomplishment that is completely separate from the goal itself? Completing a task or achieving a goal seems to be rewarding in itself, independent of the actual outcome of that task or goal. Do other animals feel this sense of accomplishment after achieving a goal? A recent study suggests that dogs might.

In their study, McGowan et al. (2013) investigated how dogs reacted to rewards after solving a puzzle compared to receiving a reward randomly. First, they trained dogs to solve various puzzles, such as pressing a lever or pushing a box over, in order to get a reward.

160px-Beagle_puppy_CadetDuring the testing phase, a dog would be led into a room containing a puzzle. In the experimental condition, the puzzle was one that the dog had been trained to solve. Once the dog solved the puzzle, a door would open, allowing the dog to access the reward. In the control condition, the puzzle was completely new to the dog, who had no idea how to solve it. The door to the reward would open randomly, regardless of what the dog did. The important difference between these two conditions is that in the first (experimental), the dog had control over access to the reward, whereas in the second (control), she did not.

The dogs were tested on six trials per day for six days (three days in the experimental condition, three in the control condition). Having all the dogs participate in both conditions allowed the experimenters to control for individual differences in the dogs’ temperaments.

McGowan et al. closely examined and compared the behavior of the dogs in the two conditions and made some interesting findings. First, they found that dogs in the experimental condition wagged their tails more frequently than dogs in the control condition. Conversely, dogs in the control condition chewed on the puzzle devices, but dogs in the experimental condition did not.

3059800422_015f4c45c4_mWe can easily interpret the tail-wagging results: clearly, the dogs were in a more positive emotional state while in the experimental condition than while in the control condition. The chewing behavior is a bit more difficult to interpret, but McGowan et al. suggest that it was the result of the dogs’ frustration with their inability to open the door by solving the puzzle.

Both of these behaviors were measured before the door to the reward was opened, so they can’t be attributed to receiving the reward. Rather, they suggest that the differing emotional states of the dogs in the two conditions were due to the dog solving the puzzle (or not).

(Note: Animal emotions are a source of conflict among researchers. Some insist that nonhuman animals do not have emotions, others say that they have emotions but they aren’t the same as human emotions, still others assert that nonhuman animals have the same emotions as humans, and many more researchers fall somewhere in between. For the purposes of this blog post, I’ll stick with the very vague term “positive emotion” to describe the canine equivalent of “sense of accomplishment”.)

A particularly interesting result is that in the experimental condition, the dogs were excited to go to the testing room at the start of each trial. However, in the control condition, while they showed excitement on the first couple trials, the dogs became reluctant to go to the testing room in later trials. McGowan et al. think this could be due to apathy caused by the dogs having no control over their environment (i.e. opening the door to the reward).

Overall, these results indicate that dogs, like humans, experience a positive emotion after achieving a goal that is separate from the direct result of achieving that goal (in this case, the reward). Furthermore, the behavior of the dogs in the control condition suggests that a sense of having control over the environment may play a part in this positive emotion. Which makes sense, when you think about it. If we assume that feeling like you have control over your environment is an important component of happiness or wellbeing, then achieving a goal or completing a task (i.e. changing your environment in a self-defined way) should cause a positive emotion.


McGowan et al. also used three different rewards (food, human contact, and canine contact) and compared the dogs’ responses – check out their paper for the interesting results!

Source Cited:

McGowan, Ragen TS, et al. “Positive affect and learning: exploring the “Eureka Effect” in dogs.” Animal cognition (2013): 1-11.