Category: Comparative

Baboons like to hang out with other baboons who are similar

By guest blogger Mary Bates

The saying “birds of a feather flock together” might apply to non-human primates, as well. A new study shows chacma baboons within a troop spend more of their time with baboons that they resemble, choosing to associate with those of a similar age, status, and even personality. This is known as homophily, or “love of the same.”

The researchers, led by the University of Cambridge and the Zoological Society of London, discuss these findings in light of the evolution of culture in primate societies. The research was published in May in the journal Royal Society Open Science.

Alecia Carter and her colleagues tracked two baboon troops in Namibia’s Tsaobis Nature Park over six years. All the individuals in these groups had been given personality tests to determine their boldness and propensity to either generate or exploit information. Carter and her colleagues analysed how these personality traits, along with age, dominance rank, and sex, affected how baboons associate with one another. To define an association, the researchers measured time spent in proximity and time spent grooming.

Individual animals can acquire information first-hand, by directly interacting with their environment, or socially, by paying attention to the behavior of others. An individual’s personality can affect its propensity to both generate social information (i.e. bolder baboons are more likely to act as a demonstrator) and exploit it from information generators (i.e. bolder types also tend to learn more than their shyer peers through observation).

Boldness also influences a baboon’s response to an unfamiliar food item, like a hard-boiled egg or bread roll dyed green. More confident individuals spend more time inspecting and ultimately eating a novel food while shy types stick to the food they know. And in a previous experiment, Carter and her colleagues discovered that juveniles and their bolder elders were more likely than shyer animals to learn about a novel foraging task by watching another baboon demonstrate, and to later serve as demonstrators themselves.

Given these differences in personality and propensity to either generate or use social information, the researchers next focused on which baboons hung out with one another. They found that, like humans, baboons prefer others who are similar to themselves.

Carter and her colleagues show that, especially when it comes to grooming networks, baboons show homophily for boldness, age, rank, and propensity to both generate and exploit information, but not for sex.

The problem with these patterns of assortment is that they may impede the transfer of information between individuals. Social learning allows the rapid spread of novel information among group members. It has been implicated in the formation of traditions and cultures within species. But if information-generators – those baboons more likely to solve novel foraging tasks on their own, such as younger and bolder baboons – spend their time in the company of other information-generators, their knowledge might not spread throughout the troop. In this case, homophily could preclude some individuals from learning from others.

Carter and her colleagues hope that understanding baboons’ personalities and social preferences will shed light on the conditions that may facilitate or retard the formation of culture in primate societies. It seems likely that both personalities and social networks play a role.

In baboon societies, it appears that the information producers, those individuals that find out new information, tend not to associate with individuals who need to access new social information. This would stop the formation of a tradition, as information cannot pass from informed individuals to uninformed ones. This tendency to associate with similar baboons could explain why these animals are not known for their cultural traditions in the same way that humans and great apes are. In this case, “birds of a feather flocking together” leads to cultural stagnation and a lower likelihood of new knowledge spreading throughout the group.

Although humans are known for their rich culture, Carter says that homophily could also slow down the transmission of ideas in human social groups. Conversely, diversity can help idea exchange, as shown in some tentative research on Twitter.

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Carter, A., Lee, A., Marshall, H., Tico, M., & Cowlishaw, G. (2015). Phenotypic assortment in wild primate networks: implications for the dissemination of information Royal Society Open Science, 2 (5), 140444-140444 DOI: 10.1098/rsos.140444

further reading
We sit near people who look like us

Post written by Mary Bates (@mebwriter) for the BPS Research Digest. Mary Bates is a freelance science writer specializing in the brains and behavior of humans and other animals. She has been published in National Geographic News, National Geographic’s Weird & Wild blog, New Scientist, the Society for Neuroscience’s BrainFacts website, Psychology Today, the Scientific American Mind Matters blog, on the Howard Hughes Medical Institute’s News website, as well as in other online and print publications. Her Wired Science blog, Zoologic, was published from 2013-2015. She earned her PhD from Brown University, where she researched bat echolocation and bullfrog chorusing. You can follow her on Twitter and Facebook and see all of her work at her website.

"Place cells" discovered in the rat brain

John O’Keefe
Image: Nobelprize.org

This month John O’Keefe, May-Britt Moser and Edvard Moser were awarded the Nobel Prize in Physiology or Medicine for their work identifying the brain’s “GPS system” – the internal maps that allow us to understand our position in space. The Moser’s discovery of grid cells this century built upon O’Keefe’s earlier accomplishment at UCL in London, the discovery of place cells in the brain. Here, we look back to his 1971 “Short Communication” in the journal Brain Research which presented his preliminary evidence for place cells in rats.

Earlier research had suggested that damage to a rat’s hippocampus (a bilateral brain structure in the temporal lobes) causes it to become confused when attempting spatial tasks. O’Keefe wanted to look in detail at what different hippocampal regions were up to when a rat moves around, specifically to see whether there was a neural system “which provides the animal with a cognitive, or spatial, map of its environment”.

Together with student Jonathan Dostrovsky, O’Keefe inserted microelectrodes through the skulls of 23 rats, each arriving at a slightly different position in the hippocampus. Each rat could then explore its limited environment – a 24cm by 36cm platform – while the experimenters recorded neural activity from the electrodes.

In all, the study took recordings from 76 different positions in the hippocampus. Some turned out to fire in response to particular behaviours, such as walking, eating, or grooming; some while the rat was aware of something; some during sleep; some for no detectable reason at all. But electrodes at eight locations only gave their full response “when the rat was situated in a particular part of the testing platform facing in a particular direction” (italics in original). This was the first ever discovery that different brain cells represent unique location and orientation information.

O’Keefe and Dostrovsky attempted to find straightforward explanations for this spatial sensitivity. But eliminating sound cues (by silencing fans and other unmoving sound sources) and olfactory ones (by rotating the testing platform) had no effect on the neural activity of these eight “place cells*”. This solidified the possibility that the eight weren’t responding to information arriving through the senses from “out there”, but from a representation of space that existed within the brain.

Our findings “suggest that the hippocampus provides the rest of the brain with a spatial reference map,” concluded O’Keefe and Dostrovsky. As explained by Hugo Spiers in next month’s Psychologist magazine, this evidence opened up investigations into spatial memory and cognition, which began to demand some kind of coordinate system feeding into the place cells themselves. That idea was finally cashed out by the Mosers, who established that the entorhinal cortex, a key interface between the hippocampus and the neocortex, contains grid cells that perform this function by encoding atop space grids of hexagons in a honeycomb fashion familiar to anyone who has played too many wargames.

A systematic investigation into the through-lines between neural activity, cognition and behaviour, the body of work by O’Keefe and the Mosers is groundbreaking, genuinely surprising, and provides fertile ground for continued exploration, not only of rats, but of ourselves: minds within bodies within space.
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  ResearchBlogging.orgO’Keefe, J., & Dostrovsky, J. (1971). The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat Brain Research, 34 (1), 171-175 DOI: 10.1016/0006-8993(71)90358-1

*note the term “place cell” was not used in this paper.

Post written by Alex Fradera (@alexfradera) for the BPS Research Digest.

Rats outperformed humans on this learning task

We like to think of ourselves as the top of the class when it comes to intelligence in the animal kingdom. Our inventions and scientific progress are testament to that claim, and yet there are some ways in which our complex brains let us down. In this new study researchers led by Ben Vermaercke compared human and rat performance on two forms of category-based learning. On one of them, the rodents trounced the homo sapiens.

The participants – 16 rats and 24 humans – were trained to recognise that certain patterns (stripes of light and dark, known as gratings) shown on a screen were the targets, while others were the distractors. The patterns were presented in pairs, and for the rats, if they followed the target pattern in a pair, this led them to the correct route (out of two) towards the safety of a platform in a water maze. For humans, choosing the target pattern simply led to presentation of a “correct” symbol – a green triangle pointing upwards; choosing the distractor pattern triggered a downward red triangle.

Through choosing the different patterns and receiving feedback, the rats and humans learned which patterns were targets and which were distractors. In one “rule based” version of the task, the targets and distractors always differed only along one dimension – either the frequency, or the orientation, of the light and dark stripes. In the other “information integration” version of the task, the targets differed from the distractors along both dimensions (frequency and orientation) simultaneously.

The key challenge occurred next, when the rats and humans entered the test phase, and attempted to generalise what they’d learned in the training phase to new pairs of patterns. The rats and humans performed similarly on the rule-based version of the task. However, when it came to the “information integration” version, the rats performed significantly better than the humans. This was because the humans’ performance dipped in the “integrated information” version of the task, whereas the rats performed just as well at this version as they did on the rule-based version.

What was going on? In the version of the task where the target was distinguishable from the distractors along two dimensions simultaneously, the correct choice couldn’t be identified based on a simple rule. But humans like to make conscious decisions and use explicit rules, even when this approach isn’t optimal. It’s for this reason that they struggled at this version of the task. Rats, in contrast, used an implicit similarity approach in both versions of the task (think of this as going with your gut, as to which pattern seemed most similar to the targets seen in training). This served the rodents fine in the “rule-based” version, and actually led them to beat us humans in the more complex information-integration version. In this latter version, the humans looked too hard for an explicit rule, and would likely have performed better if they’d gone with their instincts.

“We have shown that rats display superior generalisation performance in a generalisation context in which correct stimulus-response associations do not follow a dimension-based rule,” the researchers said. “This is in line with the hypothesised competition in the human brain between an explicit, rule based system and in implicit category-learning system.”

_________________________________ ResearchBlogging.org

Vermaercke B, Cop E, Willems S, D’Hooge R, & Op de Beeck HP (2014). More complex brains are not always better: rats outperform humans in implicit category-based generalization by implementing a similarity-based strategy. Psychonomic bulletin & review, 21 (4), 1080-6 PMID: 24408657

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

The evolutionary roots of laughter

To evolutionary psychologists, the noise made by gorillas, chimps and bonobos when you tickle their feet is no laughing matter. These distinctive vocalisations suggest that rather than evolving separately, laughter evolved in a shared common ancestor before becoming tailored in each primate species, including humans.

To find support for this idea, Diana Szameitat and her colleagues scanned the brains of 18 men and women whilst they listened to the sound of human tickle-induced laughter as well as laughter prompted by joy and taunting. The researchers found a ‘double-dissociation’ – the tickle laughter provoked extra activity in the secondary auditory cortex, likely reflecting the acoustical complexity of this kind of laughter, whereas the joy and taunting laughter prompted more activity in the medial frontal cortex, a region associated with social and emotional processing. These differences were observed whether the participants were tasked with categorising the laughter they heard, or merely with counting the number of laughs. The finding suggests that humans produce and process an evolutionarily ‘old’ form of tickle-based laughter, which is shared with non-human primates, as well as a newer, more emotionally sophisticated variant.

The laughter stimuli were provided by a team of eight professional actors using ‘auto induction’ techniques. This means they used their imagination, memories, and body movements to provoke the required emotions and bodily sensations in themselves as far as they could. The researchers said they only selected laughter samples that had been accurately categorised (as joy, taunting, or tickle laughter) in pilot work at well above chance levels by naive listeners. The dependence on acted laughter does seem to be a weakness of the study, however, especially as it’s a well-documented fact that people are unable to tickle themselves.

‘Our study provides suggestive evidence that laughter, in the form of a reflex-like reaction to touch, has been adopted into human social behaviour from animal behaviour,’ the researchers said. ‘Through the differentiation of human social interaction over time this “simple” form of laughter may have diversified to become a spectrum of different laughter variants in order to accommodate increased complexity of human social interaction.’
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ResearchBlogging.orgSzameitat, D., Kreifelts, B., Alter, K., Szameitat, A., Sterr, A., Grodd, W., and Wildgruber, D. (2010). It is not always tickling: Distinct cerebral responses during perception of different laughter types. NeuroImage, 53 (4), 1264-1271 DOI: 10.1016/j.neuroimage.2010.06.028

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Mice and humans like the same smells

We share more in common with mice than a penchant for cheese, we also like the same kinds of smells. This suggests that our nasal preferences, even for biologically insignificant smells, are somewhat hard-wired or predetermined, and not entirely learned.

Nathalie Mandairon and colleagues asked thirty participants to rate their preference for a range of odours including geraniol, which has a floral smell, and guaiacol, which has a smoky whiff about it. The odours that the participants said they favoured, such as geraniol, tended to be the same ones that thirty mice spent the most amount of time sniffing, whereas the odours the humans liked least, such as guaiacol, tended to be the ones the mice were least interested in.

Importantly, the smells used in the study were varied and had no apparent biological significance. For example, it wasn’t just the case that humans and mice both disliked smells that signalled rotten food or that signalled danger.

“Even if pleasantness is the result of culture, life experience and learning,” the researchers said, “the present interspecies comparison shows that there is an initial part of the percept which is innate and engraved in the odourant structure.”

Just what it is about the chemical structure of some substances that makes them smell pleasant to mice and humans remains to be discovered. “Taken as a whole, these results substantially affect our view of olfactory [smell-based] hedonic perception and open up new avenues for the understanding of its neural mechanisms,” the researchers concluded. “They also suggest that odour exploration behaviour in mice may be used to predict human olfactory preferences.”
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ResearchBlogging.orgNathalie Mandairon, Johan Poncelet, Moustafa Bensafi, Anne Didier (2009). Humans and Mice Express Similar Olfactory Preferences PLoS ONE, 4 (1) DOI: 10.1371/journal.pone.0004209

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Cognitive dissonance observed in children and monkeys

Roast beef or chicken for dinner? Spain or Greece for a holiday? If we believe two or more options are equally appealing, yet we have to plump for just one choice, it can cause us psychological discomfort – what psychologists call ‘cognitive dissonance’.

Having made a decision, say, for chicken or Greece, what people often do to alleviate this dissonance, is update their attitudes to match the choice they made – the beef would have been too rare, Spain would have been too hot. Remarkably, psychologists at Yale University have now shown that young children and monkeys engage in these sorts of thought processes too.

Forty 4-year-olds used a scale of smiley faces to indicate how much they liked a range of animal stickers. For each child, the researchers identified three stickers which that child liked equally – let’s call these A, B, C. Each child then faced two choices – first to choose which of A or B they would like to take home. Afterwards, they then had to choose between sticker C and whichever sticker (A or B) they hadn’t selected before.

In the latter case, if the children liked the stickers equally, then on average they should have opted for sticker C over either A or B 50 per cent of the time, but in fact sticker C was selected in 63 per cent of such choices. The reason, the researchers say, is because, to reduce cognitive dissonance, the children had downplayed the appeal of whichever sticker (A or B) they had chosen not to pick earlier, thus tipping the balance in favour of C.

Moreover, the same pattern was found in an almost identical experiment with six capuchin monkeys who chose between different coloured, equally appealing M&M sweets. After a given colour was rejected, its future appeal suffered as the monkeys appeared to update their attitudes to match their earlier choices.

“Our findings hint that some of the mechanisms that drive cognitive-dissonance-reduction processes in human adults may emerge as a result of developmentally and evolutionarily constrained systems that are consistent across cultures, ages, and even species,” Louisa Egan and colleagues concluded.
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Egan, L.C., Santos, L.R. & Bloom, P. (2007). The origins of cognitive dissonance. Evidence from children and monkeys. Psychological Science, 18, 978-983.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Hat tip to The Proper Study of Mankind where further discussion and analysis can be found.

Who’s the daddy?

Image by Raimond SpekkingBeing a father profoundly alters the structure of your brain – at least it does if you’re a marmoset monkey. Yevgenia Kozorovitskiy and colleagues at Princeton University psychology department used staining techniques to compare the brain structure of male marmoset fathers with the brain structure of male marmosets who had never fathered an infant. Marmoset fathers are unusual among mammals because they care extensively for their offspring, spending large amounts of time carrying and feeding them.

The researchers found that compared with non-fathers, there was a marked increase in the connective branching between brain cells in the front of the marmoset fathers’ brains. Kozorovitskiy told The Digest that this could lead to enhanced information processing, thus promoting paternal behaviour. “Paternal behaviour in marmosets is a complex task, indeed – the infants must be watched over, picked up whenever necessary and handed back to the mother for feeding at regular intervals”, she said. The marmoset fathers’ brains also had an increased number of receptors for vasopressin, a hormone that’s known to be associated with bonding.

But how relevant is this research to human fathers? Kozorovitskiy again: “Since many human fathers are intimately involved in child-care, their brains might show somewhat similar changes. Yet, male marmosets are extremely engaged fathers and carry their offspring almost all the time during the first month or two of the infant’s life, and it remains to be seen how the brains of human dads measure up”.

In some ways this research is hardly surprising – from taxi-driving to juggling, countless studies have demonstrated how the brain’s structure changes to meet the demands placed on it. Indeed, Kozorovitskiy’s team are planning experiments to find out if the brain changes they observed in marmoset fathers will also be found among any marmoset that raises young, whether it’s the natural parent or not.
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Kozorovitskiy, Y., Hughes, M., Lee, K. & Gould, E. (2006). Fatherhood affects dendritic spines and vasopressin V1a receptors in the primate prefrontal cortex. Nature Neuroscience, In Press. DOI:10.1038/nnl1753.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Marmoset image courtesy of Wikipedia Commons.

Chimps and toddlers lend a helping hand

It’s been argued that only humans display truly altruistic behaviour, but now, under laboratory conditions, Michael Tomasello and colleagues at the Max Planck Institute of Evolutionary Anthropology have observed altruistic behaviour by chimpanzees towards a human experimenter, suggesting we’re not so unique after all. They’ve also observed surprising degrees of altruistic helping by 18-month old children.

Three young chimpanzees were observed helping a human experimenter reach items she’d dropped or couldn’t reach. They helped without verbal prompting, training or any form of reward or punishment (see movie). However, they didn’t help when the experimenter’s needs were more complicated – for example they didn’t open the doors to a cabinet when she had her hands full.

In a related study, Tomasello’s group also observed chimps letting another chimp in from an adjacent room when they needed help reaching a food platform, and that given a choice, they chose the more able chimp from two potential collaborators (see movie). “The implication is that human forms of collaboration are built on a foundation of evolutionary precursors that are present in chimpanzees and a variety of other primate species”, the researchers said.

Tomasello found the altruism shown by 18-month old infants was even more extensive – they helped a researcher reach things he’d dropped but also did things like open a cabinet door so he could place books inside (see movie). Again this behaviour was observed without any verbal requests for help or any reward or praise. And importantly, the infants (and chimps) rarely helped in control conditions – for example, if the researcher deliberately threw something on the floor, or clearly intended to place books on top of the cabinet rather than inside.

“Children and chimpanzees are both willing to help, but they appear to differ in their ability to interpret the other’s need for help in different situations,” the researchers said.

The observed altruism in chimpanzees appears to contradict an earlier study that showed chimps tended not to share food with others when given the opportunity at no cost to themselves. However, Tomasello and colleagues suggest that study may not have used ideal conditions to study altruism because chimps are notoriously competitive with each other when it comes to food.
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Warneken, F. & Tomasello, M. (2006). Altruistic helping in human infants and young chimpanzees. Science, 311, 1301-1302.
Melis, A.P., Hare, B., Tomasello, M. (2006). Chimpanzees recruit the best collaborators.Science, 311, 1297-1300.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Why perform psychology experiments on rats?

Following readers’ criticisms of the research behind the item “Phew! How rats sigh when they’re relieved” (see comments under previous post), the Digest invited lead author of that research, Dr. Stefan Soltysik, to defend his study. To continue the debate, please do use the ‘comments’ function at the bottom of this post. First, here’s what Dr. Soltysik had to say:

I am grateful for the comments addressed to some aspects of the paper: “In Rats, Sighs Correlate with Relief.” I would like to initiate a dialogue to promote mutual understanding.

First about pain experiences in experiments.

In reply to those (Karen, Freya, Richard, Dave S.) justly concerned with the use of pain in behavioural experiments, I would like to offer a few words of explanation. This explanation does not apply to many studies where excessive electric shocks are used, but does apply to a great many behavioural studies, such as this one, in which the animals are required to exhibit normal emotional states.

The expression ‘tail-shock‘ sounds bad if one does not realize that five brief and mild pain incidents per day is the least of unpleasant experiences the rats may go through in normal life. Not only do they inflict more harm on each other in normal fighting, but the effects of bites or scratches could be much more painful, prolonged, dangerous, and even lethal. Animals trained with the use of pain, such as in this study, are spared long-lasting unpleasant experiences of hunger, thirst, low or high ambient temperature, anxiety, cutaneous itch or swellings from lice or other parasites – all of which are normal in “natural life conditions.”

Both I and my co-workers regularly tried the electric shock on ourselves. It wasn’t pleasant but was certainly preferable to a rat’s bite. Our entire experiment had to be very tolerable for the rats, because they needed to learn when it was safe and when not. They wouldn’t have been able to learn to relax and feel relief if the training was more disturbing. The same intensity of shock was used on cats in previous studies and to our surprise and satisfaction, many of these cats purred and fell asleep between trials. Both our cats and rats, when handled before and after the daily session, were quiet and friendly.

If it is accepted that there is a need to study emotional states of anxiety, fear and relief, then the administration – carefully and as humanely as possible – of pain is inevitable. Pain is not an abnormal experience – some cultural attitudes not withstanding – and a total lack of it (pain deprivation) may be deleterious to normal non-exaggerated responding to it and future coping with it.

As to the question of “scientific interest” and “benefit …. for humanity” (Karen, Louise) or replacing rats with humans (Dave Stevens – you probably think of paid volunteers, but I’ve even received suggestions of using inmates), consider this:

First, it is interesting per se, to find common psycho-physiologic grounds between our and other animals’ behaviour and “psyche.” Second, such commonality allows us to explore new ways (treatments, drugs) for dealing with human suffering (anxieties, depressions, phobias etc.). I do not know of any other procedure or behavioural test, or physiological index, that compares anxiety and relief, which would provide 20-fold (2000%) difference in objective measurements (it is usually measured in fractions, like 35% or so). Our rats sigh approx. 25 times/hour spontaneously, less than 10/h when anxious, but more than 180/h when relieved! So, consider, if you really have experimental animals` wellbeing in mind and not just negative feeling about any animal experimentation, that far fewer animals will be required to test a new psychotropic drug or some other procedure, when measuring emotional states (using sighs instead of heart rate, blood pressure etc.) is so dramatically improved (as demonstrated by the current study). And third, why not humans? Indeed, why not? I am sure now that rats have pioneered this approach, studies of human sighing should be considered as one of many other possible steps. But, humans seem diverged from other mammals (rats?) in that they use sighs in many emotional contexts: We sigh with relief, but also for something, to somebody, with disappointment, in frustrations, when resenting, etc. etc. That complicates things, unfortunately.Our paradigm that elicits in the rat three emotions (anxiety, fear and relief) reliably within 15 seconds of each trial has undeniable simplicity. So please, try to accept the possibility that mild aversive experiences and clear-cut highly significant results will benefit both humanity (leading to the fast reliable testing of new drugs) and animals (because fewer will be needed to obtain results).

Stefan Soltysik

Phew! How rats sigh when they’re relieved

If you ever hear a rat sigh, don’t worry it’s not because they’re getting impatient, rather it’s because they’re relieved, a behaviour that probably evolved as a safety signal to other rats. That’s according to Stefan Soltysik and Piotr Jelen at the Limbic System Laboratory of the Nencki Institute of Experimental Biology in Warsaw.

Over hundreds of trials, Soltysik and Jelen trained 16 rats to expect an electric shock to their tail after they heard an auditory tone, but not to expect a shock if a light came on after the tone. In this way, fear could be induced in the rats, followed by relief if they saw the light come on. All the while, the researchers monitored the rats’ breathing by recording their diaphragm muscles. Sighs are easily recognisable, the researchers explained, because they appear as a “deep ‘additional’ inhalation that starts at or around the peak of a normal respiratory cycle”.

Three hundred and eleven sighs were recorded across the course of the experiment, the vast majority of them during the ‘relief phase’ that followed a light coming on, indicating a shock would not occur. Averaged across all the rats, 7.4 times more sighs occurred during this ‘relief phase’ than during the equivalent period when the light didn’t come on – a fear phase – that occurred between the tone sounding and a shock being given.

The researchers said it’s possible “This respiratory act was recruited during evolution to signal reduced perception of danger, and/or to synchronise the emotional state of the group (collective sighs of relief?)…” They added that “the sigh could be a signal opposite to the alarm cry”.

To test this theory further they plan experiments to see if sighing is more prevalent in the company of other rats, and to test whether sighing is impaired in rats raised in social isolation.
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Soltysik, S. & Jelen, P. (2005). In rats, sighs correlate with relief. Physiology and behaviour, 85, 598-602.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.