Category: Comparative

Researchers are studying psychopathic chimps to better understand the human variety

GettyImages-584864828.jpgBy Emma Young

To understand the drivers of a psychopathic personality (marked by callousness, disinhibition and superficial charm), it’s worth looking at our closest relatives. Some chimps, like some people, score highly on scales designed to evaluate psychopathic tendencies. And new work in Frontiers in Neuroscience reveals a potentially important genetic contributor to psychopathic traits in chimps, which could lead to a better understanding of the traits in people.

Continue reading “Researchers are studying psychopathic chimps to better understand the human variety”

The idea that humans have a poor sense of smell is an outdated myth, argues new review

The Nose For Wine
It’s estimated that humans may be able to distinguish up to a trillion different smells

By Alex Fradera

In the early 1950s, while investigating rabbits’ sense of smell by recording the activity of their brain cells, the scientist Lord Adrian noticed something curious. As his team mixed up odours of increasing strength, to see at what point the rabbits’ neurons fired in response, they found the critical threshold appeared around the same point that they were able to smell the odour themselves: in other words, this suggested that the smell had become noticeable to animal and man at the same time.

On publication of the research, Lord Adrian mentioned his observation, but it didn’t provoke a serious response, presumably because informed scientists knew that the human sense of smell is generally pathetic. Everyone knew… but they knew wrong. In a new review in Science, John McGann, who runs the Rutgers Laboratory on the Neurobiology of Sensory Cognition, takes us through the historical misunderstandings to reach the truth about what the human nose knows.

Continue reading “The idea that humans have a poor sense of smell is an outdated myth, argues new review”

Brain scan study reveals dogs attend to word meaning, not just intonation

By guest blogger Sofia Deleniv

Imagine if we could capture the words of an angry dog owner holding a chewed-up shoe – “How could you? You terrible dog!” – and digitally alter the tone to sound praising. Would the dog be oblivious to the reprimanding content of the message? I should admit that, until quite recently, I thought that the answer was yes ­– that no matter how chastising the words you used, you could convince a dog that it is being showered in praise, simply by adopting an affectionate tone. But a recent study published in Science indicates that many of us might be vastly underestimating canine listening skills. The findings reveal that dogs do not rely exclusively on intonation when judging the reward value of human speech, but that they also recognise the meanings that we assign to words. Continue reading “Brain scan study reveals dogs attend to word meaning, not just intonation”

New clues about the way memory works in infancy

Neurons in the beautiful background. 3d illustration of a highBy Alex Fradera 

Can we form memories when we are very young? Humans and non-humans alike show an “infantile amnesic period” – we have no memory of anything that happens during this time (usually up to age three or four in humans) which might suggest we can’t form very early memories. But of course it might be that we can form memories in these early years, it’s just that they are later forgotten. The idea that at least something is retained from infancy is consistent with the fact that disorders present in adult life can be associated with very early life events.

Now Nature Neuroscience has published a paper confirming that in rats some kind of memories are created during the amnesic period, but that these operate differently and are produced by different brain chemistry from adult memories. What’s more, such events may have a role in kickstarting memory system maturation. Continue reading “New clues about the way memory works in infancy”

Pessimistic rats are extra sensitive to negative feedback

By guest blogger Mary Bates

Depression is complex and influenced by many factors, but the way depressed people think is a likely contributor to the disorder. Depression is often associated with cognitive biases, including paying more attention to negative than positive events and recalling them more easily. People with depression also tend to ruminate over perceived failures and criticism, and they are extra sensitive to negative feedback.

Analogous cognitive biases can be found in animals. Now, in a new study, researchers have demonstrated for the first time a link between pessimism and sensitivity to performance feedback in rats. It’s the latest finding to show parallels between human depression and rat pessimism – an important result that lends further legitimacy to using animal research to shed light on human psychological problems.

You might wonder how on earth it is possible to measure pessimism in rats.  One way to do this was shown in a 2004 study in which animals were trained to press a lever to receive a food reward in response to hearing one tone, and to press a different lever to avoid a mild electric shock upon hearing a different tone. Then the scientists presented the animals with intermediate tones, in between the ones that signaled either food or shock. Which lever the rats pressed in response to these ambiguous cues was considered an indicator of whether the animals expected a positive or negative event. In other words, their behaviour revealed their relative optimism or pessimism.

In the new research, Rafal Rygula and Piotr Popik of the Polish Academy of Sciences used the same paradigm to compare the reaction of rats displaying optimistic and pessimistic traits to positive and negative feedback. First, they divided rats into two groups based on how they performed in the ambiguous-cue interpretation test. Some rats tended to interpret ambiguous cues as signaling a reward, indicating a positive cognitive bias, while others were more likely to interpret them as signaling punishment, indicating a bias toward more pessimistic judgments.

Then the optimistic and pessimistic rats were trained and tested in a probabilistic reversal-learning (PRL) task, which essentially involves using negative or positive feedback to teach the animals to change or maintain a response that they’ve learned previously. Rygula and Popik determined how likely each rat was to switch its response after receiving negative feedback and to maintain its response following positive feedback.

The researchers found that the two groups did not differ in their responses to positive feedback, but that pessimistic rats were more sensitive to negative feedback than optimistic rats. That is, the pessimistic rats were much quicker to drop a previously learned response once it started to be met with negative feedback – you could see this as akin to a depressed human giving up more quickly in response to criticism.

This new finding builds on earlier research by Rygula and his colleagues, in which they demonstrated that the trait of pessimism can also influence rats’ motivation levels (the optimistic rats were more motivated than pessimistic rats to obtain a sip of sugary water), and their vulnerability to “stress-induced anhedonia” – after being restrained, which they find stressful, pessimistic rats showed a longer-lasting lost appetite for sugary water. This might represent a reduction in their ability to experience pleasure that is analogous to human anhedonia, which is another important symptom of depression.

This new study on sensitivity to negative feedback in pessimistic rats, in combination with Rygula’s two previous studies, supports the claim that rats that tend to be pessimistic are also more likely to demonstrate a variety of behavioral and cognitive processes that are linked with increased vulnerability to depression.

It’s hard to know how similar pessimistic rats are to depressed people, but studies like these certainly provide intriguing commonalities. Scientists use animals such as rats as models for human disorders like depression, and use such models to test new therapies and drugs. It seems that rats can display the same negative cognitive biases as people, tending to make negative judgments about events and interpreting ambiguous cues unfavorably. And these biases, in turn, affect both rats’ and humans’ sensitivity to negative feedback.

Post written by Mary Bates (@mebwriter) for the BPS Research Digest. Mary is a freelance science writer specialising in the brains and behaviour 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, plus many other outlets. 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.

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Rats can be trained to perform search and rescue missions

Step aside batman and superman, there’s a new hero in town

By guest blogger Mary Bates

Search and rescue dogs are commonly used to find people trapped in the debris of collapsed buildings, but are search and rescue rats next? A new study suggests the rodents can be trained to find people and then return to their release point after hearing a signal.

The study was conducted by researchers at Western Michigan University and APOPO, a Belgian nongovernmental organization that has previously trained giant African pouched rats (Cricetomys gambianus) to sniff out landmines and tuberculosis.

Pouched rats have the potential to make even better search and rescue animals than man’s best friend. Dogs can take years to train, are inconvenient to transport, and, because of their size, cannot penetrate rubble but have to search for scent as they move over and around it. Giant African pouched rats, native to sub-Saharan Africa, are agile and climb well. They should have little difficulty moving among debris. Like dogs, they have a keen sense of smell. These rats are relatively inexpensive to house, train, and transport, and unlike dogs, they do not depend on a particular human handler to work well. Pouched rats can live more than eight years in captivity, so early investment in training can pay off over a protracted period. Finally, the rats are large enough (adults have body lengths between 25-45 cm and weigh 1-2 kg) to carry appropriate equipment. In this study, that equipment was a small video camera and a beeper to signal the rat to return to its release point.

For more than 10 years, APOPO has been training pouched rats to sniff out landmines by rewarding them in a series of training stages that increasingly resemble real-world conditions. For the new study, the researchers tested whether the same technique could be used to train rats to find people in collapsed buildings.

The first stage of training was socialization. From three to six weeks of age, the rats were handled by people and exposed to different sights, sounds, and smells as they were hand fed treats like peanuts and bananas. During this time, the rats were also fitted with backpacks that held a miniature video camera and small beeper, to which they readily habituated.

Next, the researchers trained the rats to approach and place their paws on a target person and then return to their starting point at the sound of a beep. Gradually, they increased the distance the rats had to cover and added obstacles that simulated a collapsed building, like damaged wood and furniture. The target people eventually hid beneath and behind the obstacles, requiring the rats to walk through and climb over the debris to contact them. In order to receive their tasty rewards, the rats had to reach the target person and then return to their handler.

The rats were first trained in a 5 x 5 m area. When they reached more than 87 per cent accuracy, they moved on to a larger (6 x 9 m) area that contained even more obstacles. On average, it took the rats 21 sessions to reach 80 per cent or greater accuracy in this larger area.

Then the rats were put to the test. This time the rubble could be hiding a person, a bag containing recently-worn clothing, or an empty bag. Each of the five rats tested located the human target most often and the empty bag least often. Overall, rats found the target within three minutes on 83 per cent of human target trials, 37 per cent of clothing trials, and 11 per cent of empty bag trials, so they seemed to find the challenge of locating humans the easiest of all. Moreover, each rat spent the most time in proximity of the hidden person and the least time near the empty bag.

The researchers say it’s not surprising that pouched rats can be trained to sniff out people; the interesting finding is that both searching for humans and returning on command were easily trained together. Both these behaviors will be necessary if the rats are to be used to search for survivors in collapsed buildings. In a real-life situation, the rat would leave the handler, search for and find a person buried in rubble, and then return to the release point at the signal so the handler could examine the video captured by the rat for signs of survivors.

This study provides proof of principle, but the researchers say a great deal of behavioral research will be needed to produce working search and rescue rats. Even under the simplified testing conditions, the rats sometimes failed to locate the person. Multiple rats searching an area together might be required in real life conditions, as APOPO does with its landmine detecting rats.

Also, if pouched rats are to be useful search and rescue animals, they will have to perform in even more challenging conditions. More research is required to investigate the effects of variables like the presence of dust or smoke, temperature extremes, and a much larger area. The animals might have to wear muzzles to prevent them from eating any food they find, and be taught to continue searching despite the presence of food or other interesting distractions.

And what about some people’s antipathy towards rodents? “Trained pouched rats are friendly and attractive animals, but they are rats nonetheless,” note the authors. They suggest a small light might be included to allow a camera to operate and inform survivors that the rat is a trained search animal and not a wild scavenger. Rats could also carry a reassuring printed message to that effect.

Landmines, tuberculosis, and now people under debris – APOPO is just scratching the surface of what rats can do for humans.


La Londe, K., Mahoney, A., Edwards, T., Cox, C., Weetjens, B., Durgin, A., & Poling, A. (2015). Training pouched rats to find people Journal of Applied Behavior Analysis, 48 (1), 1-10 DOI: 10.1002/jaba.181

Post written by Mary Bates (@mebwriter) for the BPS Research Digest. Mary Bates is a freelance science writer specialising in the brains and behaviour 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, plus many other outlets. 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.

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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.


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

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.

  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.”


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.’

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.