Risky Business: Ape Style

A repost of an original article from April 3, 2013.

The decisions of this chimpanzee living in the
Tchimpounga Chimpanzee Sanctuary are affected
by his social situation. Photo by Alex Rosati.

If you have a choice between a prize that is awesome half the time and totally lame the other half of the time or a mediocre prize that is a sure-thing, which would you choose? Your choice probably depends on your personality somewhat. It may also depend on your needs and your mood. And it can depend on social contexts, like if you’re competing with someone or if you’re being watched by your boss or someone you have a crush on.

All animals have to make choices. Some choices are obvious: Choose the thing that is known to be of high quality over the thing that is known to be of low quality. But usually, the qualities of some options are uncertain and choosing them can be risky. As with us, the likelihood of some primates, birds, and insects to choose riskier options over safer ones can be affected by outside influences. And we aren’t the only species to have our risk-taking choices influenced by social context.

Anthropologists Alex Rosati and Brian Hare at Duke University tested two ape species, chimpanzees and bonobos, in their willingness to choose the riskier option in different social situations. They tested chimpanzees living in the Tchimpounga Chimpanzee Sanctuary and bonobos in the Lola ya Bonobo Sanctuary, both in the Democratic Republic of Congo. Most of the apes living in these sanctuaries are confiscated from poachers that captured them from the wild for the pet trade and for bushmeat. In these sanctuaries the animals live in social groups, generally spending their days roaming large tracts of tropical forest and their nights in indoor dormitories. This lifestyle rehabilitates their bodies and minds, resulting in psychologically healthy sanctuary inhabitants.

It is in these familiar dormitories that Alex and Brian tested the apes’ propensity for making risky choices. For their experimental set-up, an experimenter sat across a table from an ape and offered them two options: an overturned bowl that always covered a treat that the apes kinda like (peanuts) versus an overturned bowl that covered either an awesome treat (banana or apple) or a lousy treat (cucumber or lettuce). In this paradigm, the peanut-bowl represents the safe choice because whenever the ape chooses it, they know they’re getting peanuts. But the other bowl is the risky choice, because half the time they get fruit (yum!), but the other half of the time they get greens (bummer).


This figure from Rosati and Hare's 2012 Animal Behavour paper shows Alex demonstrating the steps they would go through before the ape chose one of the two options.

After spending some time training the apes to be sure they understood the game, the researchers tested their choices in different social situations. In each test session, the ape was allowed to choose between the two bowls (and eat the reward) multiple times (each choice was called a trial). But before the test session began and in between choice trials, another experimenter sat with the ape for two minutes and did one of three things: In one group, the experimenter sat at the table and silently looked down (they called this the “neutral condition”). In another group, the experimenter repeatedly offered the ape a large piece of food, pulling it away and grunting whenever the ape reached for it (they called this the “competitive condition”). In a third group, the experimenter tickled and played with the ape (they called this the “play condition”).

Alex and Brian found out that whereas bonobos chose the safe option and the risky option about equally, the chimpanzees were significantly more likely to choose the risky option. But despite this species difference, both species chose the risky option more often in the “competitive condition”. Neither species increased their risk-taking in the “play condition”.

The graph on the left shows that wheras bonobos chose the safe option and the risky option each about 50% of the time (where the dashed line is), the chimpanzees chose the risky option much more often. The graph on the right shows that both species chose the risky option more often in the "competition condition" than they did in the "neutral condition". Figure from Rosati and Hare's 2012 Animal Behavour paper.

These are interesting findings, especially when you consider the natural behaviors and lifestyles of these closely related species. Bonobos can be thought of as the hippies of the ape world, happily sharing and using sex to settle disputes and strengthen relationships. In comparison, chimpanzees are more like gangsters, aggressively fighting over resources and dominance ranks. So in general, the more competitive species is more likely to take risks. But when the social environment becomes more competitive, both species up the ante. This effect doesn’t seem to be simply the result of being in a social situation, because the apes didn’t increase their risk-taking in the presence of a playful experimenter.

This still leaves us with some questions to ponder though. Are apes more likely to take risks when an experimenter is offering food and taking it away because of a heightened sense of competition, or is this the result of frustration? And would we see the same effect if the “competitor” were another ape of the same species, rather than a human experimenter? How would their behavior change if they were hungry? These questions are harder to get at, but this research does demonstrate that like in humans, the decision-making process in chimpanzees and bonobos is dependent on social context.


Want to know more? Check this out:

Rosati, A., & Hare, B. (2012). Decision making across social contexts: competition increases preferences for risk in chimpanzees and bonobos Animal Behaviour, 84 (4), 869-879 DOI: 10.1016/j.anbehav.2012.07.010

The Love Chemical of 2018

Hello and welcome to the Love Chemical Pageant Results Show! The voting results are in, and today we get to crown the Love Chemical of 2018… Vasopressin! Now let’s get to know Vasopressin a little bit better.

Vasopressin (also known as Antidiuretic Hormone) is a molecule that is widely involved in the balance of water and ions (such as salts) in mammals. (Other taxonomic groups have variations of it as well). But this chemical has gone to our heads, influencing behavior as well.

In the brain, vasopressin acts on a specific receptor type, called vasopressin 1a receptor (V1aR). There are lots of V1aR receptors in brain areas that regulate social and emotional behaviors. When vasopressin binds to many of these receptors, it can result in aggression, territoriality, and fight-or-flight responses. It is also involved in the formation of memories that are necessary to avoid danger. Interestingly, males and females usually have different patterns of where in the brain these V1aR receptors are.

Although we often think of love and aggression as opposites, the life-preserving roles of vasopressin have made it well-suited to become an important chemical of love. In animals, pair bonding (the formation of a strong and unique connection between mates of a socially monogamous species) is often accompanied by an increase in aggression towards non-mates. This aggression can serve to protect the mate and family, but also to reject competitive suitors towards either partner.

Photo of a prairie vole pair from Young, Gobrogge, Liu and Wang paper
in Frontiers in Neuroendocrinology (2011)

Researchers often use several closely-related vole species to study how the brain regulates pair bonding; While prairie voles and pine voles are monogamous, raise their offspring with their partners, and defend their homes and families, montane voles and meadow voles are promiscuous and females raise their young by themselves. Oddly, giving monogamous vole species vasopressin increases their preference for spending time with their mate, their parental behaviors, and their selective aggression against outsiders, but giving promiscuous vole species vasopressin does not. Vasopressin is also more likely to increase these monogamous behaviors in males more than in females. Both males and females respond differently to vasopressin depending on their reproductive status.

It turns out, the pattern of V1aR receptors in the brain is similar between the monogamous prairie and pine voles, but different from the promiscuous montane and meadow voles. Genetic factors drive this difference, and if you alter the gene for the V1aR of a promiscuous species to be more like the prairie vole’s version of the gene, the previously promiscuous species behaves in a monogamous way! The reason promiscuous vole species don’t behave in a monogamous way when given vasopressin is because they don’t naturally have the V1aR receptors in certain brain regions to respond to it that way.

We are still learning about the role of vasopressin in pair bonding behaviors. Much of what we know has focused on these vole species, and we know much less about vasopressin’s involvement in pair bonding in other species. We also don’t know as much about the role of vasopressin in females across different reproductive stages. But one thing is for sure: Love wouldn’t be the same without Vasopressin!


Want to know more? Check these out:
Carter, C.S. (2017). The Oxytocin–vasopressin Pathway in the Context of Love and Fear. Frontiers in Endocrinology, 8(356): 1-12.

Phelps, S.M., Okhovat, M. and Berrio, A. (2017). Individual Differences in Social Behavior and Cortical Vasopressin Receptor: Genetics, Epigenetics, and Evolution. Frontiers in Endocrinology, 8(537): 1-12.

Tickerhoof, M.C. and Smith, A.S. (2017). Vasopressinergic Neurocircuitry Regulating Social Attachment in a Monogamous Species. Frontiers in Endocrinology, 8(265): 1-10.

The Love Chemical Pageant of 2018

A modified repost of an original article from February 15, 2012.

Hello and welcome to the Love Chemical Pageant of 2018! I’m your host, Miss Behavior, and YOU are the judges.

Since the beginning of…well, social animals, many hormones and neurotransmitters have been quietly working in their own ways to fill our world with love. Lately (over the last few decades), some of them have been brought out of the background and into the limelight, credited with every crush, passionate longing, parental hug, embrace among friends, and cuddle between spouses. But who truly deserves the title of The Love Chemical?

Let’s meet our contestants!

Let’s first meet our reining title-holder, Dopamine! Dopamine is a neurotransmitter produced in the brain. Sex increases dopamine levels in both males and females and blocking its effects during sex can prevent prairie voles (a monogamous species often used to test questions on pair bonding) from forming preferences for their own partner. Dopamine also plays a role in maternal and paternal behaviors.

But dopamine is not just involved in love. It has a wide range of known functions in the brain, involved in everything from voluntary movement, mood, motivation, punishment and reward, cognition, memory, learning, aggression, pain perception and sleep. Abnormally high levels of dopamine have been linked to schizophrenia and psychosis. And dopamine is especially well-known for its role in addiction... in fact, many researchers believe that we may even be addicted to our own romantic partners.

Now let’s meet Dopamine’s partner, Opioids! When natural opioids are released in the brain, they can cause a rewarding feeling that often cause us to seek more of it. When prairie voles are given drugs that prevent opioids from acting on a particular opioid receptor type (mu-opioid receptors) in a particular brain region (the caudate-putamen), they do not form pair bonds with sexual partners. Interestingly, people that see the faces of their loved ones experience lots of activity in the caudate-putamen region of the brain, especially if they rate their relationship with that person as very romantic and passionate. The caudate-putamen region of the brain also uses dopamine, so the two chemicals appear to work together there to promote the feelings of romantic love.

Please welcome Oxytocin! Oxytocin is a peptide hormone, most of which is made in the brain. Some of this oxytocin is released into the blood and affects body organs, such as the uterus and cervix during child birth and the mammary glands during breast feeding. But some of it stays in the brain and spinal cord, acting on neurons with oxytocin receptors to affect a number of behaviors. Released during child birth and nursing, oxytocin is important for helping mammalian mothers behave like moms and in species in which both parents raise young, it helps fathers behave like dads. Also released during sex, oxytocin plays an important role in pair bonding in prairie voles (particularly in the female of the pair). In humans, people given oxytocin nasal sprays have been reported to have less fear, more financial trust in strangers, increased generosity, improved memory for faces, improved recognition of social cues, and increased empathy.

But before you fall head-over-heels for oxytocin, you should know a few more things. For one thing, oxytocin isn’t exclusively linked with feel-good emotions; It has also been associated with territoriality, aggressive defense of offspring, and forming racist associations. Also, oxytocin doesn’t work alone. It has been shown to interact with vasopressin, dopamine, adrenaline and corticosterone and all these interactions affect pair bonding.

Next up is Vasopressin! Vasopressin is closely related to oxytocin. Like oxytocin receptors, vasopressin receptors are expressed in different patterns in the brains of monogamous vole species compared to promiscuous vole species. Released during sex, vasopressin plays an important role in pair bonding in monogamous prairie voles (particularly in the male of the pair). If you block vasopressin in the brain of a paired male prairie vole, he will be more likely to prefer spending time around a new female rather than his mate. On the flip side, if you increase vasopressin activity in specific brain regions of an unpaired male prairie vole or even a promiscuous male meadow vole and introduce him to a female, he will prefer spending time with her than other females. Vasopressin may also make male prairie voles more paternal.

But vasopressin does a lot of things. In the body, its primary function is to regulate water retention. In the brain, it plays a role in memory formation and territorial aggression. And even its role in monogamy is not exclusive: Vasopressin interacts with oxytocin and testosterone when working to regulate pair bonding and parental behavior.

Look out for Cortisol! Cortisol is produced by the adrenal glands (on top of the kidneys) and is involved in stress responses in humans and primates. Both men and women have increased cortisol levels when they report that they have recently fallen in love. Many studies have also found relationships between cortisol and maternal behavior in primates, but sometimes they show that cortisol increases maternal behavior and sometimes it prevents it. In rodents, where corticosterone is similar to cortisol, the story is also not very clear. Corticosterone appears to be necessary for male prairie voles to form pair bonds and it plays a role in maintaining pair bonds and promoting paternal behavior. But in female prairie voles, the opposite seems to be true! Corticosterone in females appears to prevent preference for spending time with their partner and pair bond formation.

Put your hands together for Testosterone! Testosterone is a steroid hormone and is primarily secreted from the gonads (testes in males and ovaries in females). Frequently referred to as “the male hormone”, both males and females have it and use it, although maybe a little differently. Testosterone is associated with sex drive in both men and women. But men who have recently fallen in love have lower testosterone levels than do single males, whereas women who have recently fallen in love have higher testosterone than single gals.

This is Estrogen! Estrogen is another steroid hormone, frequently referred to as “the female hormone”, although again, both males and females have it. Estrogen also seems to play a role in sex drive in both men and women. The combination of high estrogen levels and dropping progesterone levels (another steroid hormone) is critical for the development of maternal behavior in primates, sheep and rodents. But look closer and you will find that the activation of estrogen receptors in particular brain regions is associated with less sexual receptivity, parental behavior, and the preference for spending time with the mate.

So let’s have a round of applause for this year’s contenders in The Love Chemical Pageant! Now it is your turn to voice your opinion in the comments section below. Vote for the neurochemical you believe deserves the title The Love Chemical. Or suggest an alternative pageant result!


Want to know more? Check these out:

Burkett, J.P. and Young, L.J. (2012). The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction. Psychopharmacology, 224:1-26.

Fisher, H.E. (1998). Lust, attraction, and attachment in mammalian reproduction. Human Nature, 9(1) 23-52.

Marazziti, D. and Canale, D. (2004). Hormonal changes when falling in love. Psychoneuroendocrinology, 29, 931-936.

Van Anders, S.M. and Watson, N.V. (2006). Social neuroendocrinology: Effects of social contexts and behaviors on sex steroids in humans. Human Nature, 17(2), 212-237.

Young, K.A., Gobrogge, K.L., Liu, Y. and Wang, Z. (2011). The neurobiology of pair bonding: Insights from a socially monogamous rodent. Frontiers in Neuroendocrinology, 32(2011), 53-69.

Addicted to Love

Image from imagerymajestic at FreeDigitalPhotos.net.

Early exposure creates a sense of euphoria, a heightening of senses, a rush of pleasure. In order to recreate and further heighten the experience, more is sought, but the euphoric effect eventually starts to wear off. Craving and palpable longing intensifies in its absence, but the effect of exposure is now a calm relief rather than a euphoric high. And once cut off abruptly and completely, desperation, grief, pain and depression set in. The pull to return to it is (almost) insurmountable.

This describes the phases of substance addiction, listed by the DSM-5, the latest version of the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association. These phases include consumption (taking the substance), reinforcement learning (intense pleasure associated with consuming the substance), seeking more of the substance, developing a tolerance (intense pleasure is replaced with avoidance of discomfort), withdrawal (psychological and physical discomfort associated with not consuming the substance), and relapse (returning to consume the substance, even in the face of large costs of doing so).

Now re-read the first paragraph, but instead of imagining the development of a substance addiction, imagine the process of falling in love.

It sounds the same, doesn’t it? According to one theory, it sounds the same because it is the same. In essence, falling in love is the process of becoming addicted to another individual.

There are undeniable similarities between how the brain responds to substance addiction and how the brain responds to falling in love. Both substances of addiction and individuals we are attracted to cause the brain to release dopamine, a neurotransmitter, into a brain region called the nucleus accumbens. Dopamine acting in this region helps us learn to associate cues with rewarding feelings. However, dopamine acts on two different types of receptors, called D1-receptors and D2-receptors, in complex ways. Activation of D2-receptors promotes bonding with a partner; it also promotes the reward value of a substance. Activation of D1-receptors reduces bonding with a partner; it also reduces the reward value of a substance. During this time early on in a romantic relationship or early exposure to an addictive substance, dopamine is primarily acting on D2 receptors, heightening our senses and focusing our attention on the cues of our next encounter… developing our craving, our longing, our drive for the next meeting.

When we are in the early obsessive stages of love, every encounter (and especially sexual encounters) cause a pleasurable release of not just dopamine, but also natural opioids. These two brain chemicals work together in the brain to continually strengthen the association of the stimulus (the one you are falling in love with) with intense positive feelings. This will cause you to seek more and more of these interactions, craving them intensely in the times in between. These same chemicals act on the same receptors in the same way during the process of forming an addiction to a substance, causing the person to seek more and more of it.

With time, the brain adapts. Repeated encounters no longer cause the same euphoria they once did, but rather, a sense of calm contentment. The dopamine that is released before and during these encounters is now activating more of the D1-receptors, which result in less of a feeling of pleasure, and more agitation and aggression. In terms of relationships, it is thought that this transition actually helps maintain a pair bond with one individual, because in this stage you are less driven to seek a competing pair bond and you are more likely to aggressively defend the pair bond you have already established. In terms of substance abuse, this phase is called tolerance. (I know, this perspective really takes the romance out of long-term marriages, but...)

During this tolerance phase, lack of exposure to the object of your addiction (whether it is a person or a substance) results in a lack of dopamine and opioid release and an increase in stress hormone release. If we are talking about addiction to a substance, we call this withdrawal. If we are talking about a relationship, we call this separation anxiety or even heartbreak. To avoid these horrible feelings, we often relapse… right back into the arms of our addiction.

Love is not listed as a psychological disorder in the DSM-5, nor do we think of it as one. But in a true physiological sense, we may actually be addicted to the ones we love.


Want to know more? Check these out:

Burkett, J.P. and Young, L.J. (2012). The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction. Psychopharmacology, 224:1-26.

Potenza, M.N. (2014). Non-substance addictive behaviors in the context of DSM-5. Addictive Behaviors, 39(1): 1-2.