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.

Planning Ahead

Planning for the future is one of our most important – and complex – cognitive abilities. It requires the ability to make predictions about future events or states by relying on knowledge and past experiences. More basically, it requires us to disconnect ourselves from our current state, including our current emotions and motivations, to anticipate our future emotions and motivations. Scientists call this ability “mental time travel”, or chronesthesia.

As with many cognitive abilities discussed here, the mental time travel ability was initially thought to belong only to humans (the Bischof-Köhler hypothesis). However, an ingenious study done with scrub jays has demonstrated that animals may possess this ability, too.

Scrub jays, which belong to the same family as crows and magpies, cache excess food, hiding it in various places that they can access when food is scarce. This behavior may seem like planning ahead, but it could just be an automatic response to an abundance of food or the season.

Raby et al. (2007) investigated whether scrub jays could demonstrate planning for the future in a very specific way through their caching behavior. Each jay was housed in a cage divided into three compartments. The jay was fed every evening in the middle compartment. Each of the side compartments contained a caching tray, where the jay could hide food. During the day, the jay could move freely between all of the compartments. However, each morning, the jay was restricted to one of the two side compartments for two hours. In one compartment, the jay was always fed a breakfast of (uncachable) powdered pine nuts. In the other compartment, the jay was never fed breakfast, and had to wait two hours for food.

During a training phase, each jay spent a few mornings in each of the side compartments, in order to learn the associations between one compartment and breakfast, and the other compartment and no breakfast. The jay was only fed powdered pine nuts, so no caching occurred during the training phase.

After the training phase came the critical test: when given whole pine nuts (which can be cached) in the evening, would the jay cache more nuts in the no-breakfast compartment than the breakfast compartment? Such behavior would indicate that the jay was planning for the future by caching more food where it knew food would be scarce. However, if the jay cached similar amounts of nuts in both of the side compartments, then it was not planning for the future.

Raby et al. found that the jays cached significantly more nuts in the no-breakfast compartment than in the breakfast compartment, indicating that they were planning ahead. This is especially impressive because it required the jays to take into account both their future motivational state (i.e. hunger) and future available resources (breakfast or no breakfast), and suggests that they have the ability of mental time travel.

In addition to planning for the future, mental time travel also includes remembering past events (episodic memory). There’s even evidence that these cognitive processes (planning for or imagining the future and remembering or imagining the past) involve similar areas of the brain in humans!

For a more thorough discussion of mental time travel and whether non-human animals have this ability, check out this paper.


Source Cited:

Raby, Caroline R., et al. “Planning for the future by western scrub-jays.” Nature 445.7130 (2007): 919-921.