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.

Origins of The Scorpion and The Frog and the Social Brain

Starting a weekly journalistic-type blog is a daunting task, especially for someone who is holding down other jobs (as most bloggers do). But I can't be happier that I started down this path in order to share with you all these wonderfully quirky stories of animal behavior and physiology. This week, I am happy to announce that The Scorpion and the Frog turns 1! It has been a remarkable first year: We've covered topics from whale dialects, to birds that kill their "siblings", to steroids and dominance in rodents; We've learned more about the researchers that contribute this fascinating knowledge to our global society; We've had fantastic guest posts by student guest writers; We've been recognized in other blogs and with awards; But my favorite aspect of this endeavor is that we are developing a growing community of readers and animal enthusiasts from all backgrounds. So today, I would like to reflect back on how we began a year ago with a repost of the very first The Scorpion and the Frog post, The Same Clay.


The Same Clay

According to a Hopi creation myth, the world was once nothing but water and dry land. The Sun, in his daily travels across the dry land, noticed that he had not seen a single living being. The Sun mentioned this observation to Hurúing Wuhti of the east and Hurúing Wuhti of the west, the deities of all hard substances, and they decided they would make a little bird. Hurúing Wuhti of the east made a wren out of clay and covered it with a piece of native cloth. The deities then sang a song over it and the wren came to life. They sent the wren to fly all over the earth to search for anything living, which it did. When the wren returned and reported that no living being existed anywhere, Hurúing Wuhti of the west shaped the clay to form all kinds of birds and placed these clay birds under the native cloth. The deities sang over the clay birds, bringing them to life, and they taught each of them what sounds they should make and sent them to populate the earth. Hurúing Wuhti of the west then shaped the clay to form all kinds of other animals and placed these clay animals under the native cloth. The deities sang over the clay animals, bringing them to life, and they taught them each what sounds they should make and sent them to populate the earth. Hurúing Wuhti of the east then shaped the clay to form a woman and a man and placed these people under the native cloth. The deities brought them to life with their song, and they taught them language and sent them to populate the earth.


I like this myth; in particular because it illustrates that despite the awesome diversity of the animals on our planet, we are all made of the same stuff and share many similarities. At first glance, we may be amazed by eels that resist eating prey fish who are providing a dental cleaning service (like the one on the left),



or by snakes that eat animals larger than their own heads and toads that save themselves from the jaws of death by puffing up their bodies even larger than the snake can handle (like the snake and toad battling it out on the right),


or by the elaborate displays of male birds in their attempts to woo females (like the golden pheasant below),



or by kangaroo moms that guard their toddler-like young in their own bodies (like the one on the right).




But at closer inspection, we realize that all of these animals are facing similar challenges: All animals are driven to eat and not be eaten, to stay healthy, to make babies, and to keep their babies alive. And animals have developed behavioral tools to achieve these goals, such as ways of finding or making food and a place to live, ways to defend these things, techniques for attracting the opposite sex, and parental methods. The details are extremely diverse across animal groups, but the ultimate goals and many of the strategies are common. And amazingly, the brain systems that regulate these behaviors are common too.

In a new synthesis of decades of research spanning the field of behavioral neuroscience, researchers Lauren O’Connell and Hans Hofmann from the University of Texas at Austin show that despite our impressive diversity, mammals, birds, reptiles, amphibians and fish are all molded from the same metaphorical clay. They specifically focus on two brain systems, often called the social behavior network and the mesolimbic reward system.

The social behavior network is a term first described in mammals by neuroscientist Sarah Newman to describe several brain regions that are all sensitive to steroid hormones (such as testosterone and estrogen), connect to each other, and are involved in many types of social behavior (including aggression, sexual behavior and parental behavior). We now know that reptiles, birds and fish also have brain areas that are similar in how they connect to one another and what neurotransmitters and other neurochemicals they use. More importantly, these brain areas seem to relate to the same types of social behaviors in similar ways.

The mesolimbic reward system is primarily a circuit of neurons that interact using the neurotransmitter dopamine. This neural circuit is central to how the brain controls motivation and a sense of desire and reward. This system is also involved in evaluating the importance of what is being perceived in order to behave accordingly. The mesolimbic reward system has been studied most in mammals, but birds, reptiles and fish are known to seek pleasure too and similar brain structures are likely involved.

This figure from O'Connell and Hofmann's paper in the Journal of Comparative Neurology shows corresponding brain regions in mammals, birds, reptiles, amphibians and fish. The images are shown as cross-sections of the brains as if we are looking directly at the front of the animals.

O’Connell and Hofmann show that the social behavior network and mesolimbic reward system work together as a single social decision-making system. For example, if one animal comes onto the territory of another animal, the brain areas of these two systems will work together to determine if the interloper should be fought, courted, nurtured, or eaten. (Imagine the consequences of getting this decision wrong!) Although mammals, birds, reptiles, amphibians and fish have very different lifestyles and brains, most of the brain areas of this social decision-making system are present, identifiable, and most importantly, play similar roles in regulating social behavior across all these animal groups. In the end, we’re not all so different after all.

Want to know more? Check these out:

1. O'Connell, L., & Hofmann, H. (2011). The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis The Journal of Comparative Neurology, 519 (18), 3599-3639 DOI: 10.1002/cne.22735

2. O’Connell, L., & Hofmann, H. (2011). Genes, hormones, and circuits: An integrative approach to study the evolution of social behavior Frontiers in Neuroendocrinology, 32 (3), 320-335 DOI: 10.1016/j.yfrne.2010.12.004

Decisions, Decisions

It doesn't take much to notice how different animals
can be... But look closer and you'll see how similar
they are too. Figure from O'Connell and Hofmann
2011 Frontiers in Neuroendocrinology paper.

Animals live in social environments that repeatedly present both challenges (like an aggressive neighbor) and opportunities (like a flirtatious neighbor). Although animals can usually respond to such challenges and opportunities in a number of different ways, there are patterns to how animals do respond. Scientists find that animals tend to make behavioral decisions that improve their chances of survival and reproduction. To do this, they evaluate the importance of what they perceive in their environment and their own internal physiology and then respond in ways that are appropriate to the social context.

Vertebrates (animals with spinal columns, such as mammals, birds, fish, reptiles and amphibians) have amazingly similar brain anatomy and physiology to control these behavioral decision-making processes. All five of these vertebrate groups have a social behavior network (a set of brain areas that are known to be sensitive to steroid hormones and to regulate social behavior) and a mesolimbic reward system (a brain system that uses dopamine to regulate motivation, among other things). When a vertebrate is faced with a social decision, these two brain systems work together as an integrated brain network called the social decision-making network.

Drawing of a rodent brain from the side showing brain areas in the mesolimbic reward system in blue and the social behavior network in yellow. Brain areas that are part of both systems are in green. Figure from O'Connell and Hofmann 2011 Frontiers in Neuroendocrinology paper.

Researchers Lauren O’Connell and Hans Hofmann from The University of Texas at Austin compared the neurochemistry of these brain regions across 88 vertebrate species, including mammals, birds, fish, reptiles and amphibians. In each of these brain areas for each species, they looked for the presence or absence of molecules involved in the chemical signaling of important behavior modulators (dopamine, estrogen, androgen, progesterone, vasopressin/vasotocin and oxytocin).

The researchers found that despite the diversity in the animals and their ecologies, their social decision-making networks were remarkably similar. One of the most striking similarities was that receptors for all of these behavior modulators were found in the same brain areas for almost all of the animals studied. This suggests that this common distribution pattern of where these receptors are in vertebrate brains is important for helping animals make decisions that improve their survival and reproduction regardless of what their social and environmental context is. This similarity may also explain, in part, why such diverse animals show similar behaviors in similar circumstances.

Drawing comparing animal brains from the front-view from front (left side ) to back (right side). Again, brain areas in the mesolimbic reward system are in blue, brain areas in the social behavior network are in yellow, and brain areas that are part of both systems are in green. Figure from O'Connell and Hofmann 2012 Science paper.

Although O’Connell and Hofmann found strong similarities across all vertebrates, that’s not to say there weren’t differences. Interestingly, the biggest differences were found between major groups of animals. For example, the fish species studied (although similar to each other) had a different distribution of dopamine-producing neurons than did all the 4-limbed animal groups (amphibians, mammals, birds, and reptiles). Additionally, birds and reptiles have more brain areas with vasotocin- and oxytocin-producing neurons compared to the other animal groups. Changes in where these neurochemicals are produced in the brain may correspond to changes in the animals’ social environments and the behaviors best adapted to such social environments.

The approach that O’Connell and Hofmann used in this study integrated decades of research on the brains, neurochemistry and behavior of nearly 100 different species, but it shows us that when we stand back and look at the bigger picture some remarkable patterns emerge. All vertebrates, from giraffes to tree frogs to iguanas likely have very similar brain systems that work in very similar ways to regulate very similar behaviors.

Want to know more? Check these out:

1. O'Connell, L., & Hofmann, H. (2012). Evolution of a Vertebrate Social Decision-Making Network Science, 336 (6085), 1154-1157 DOI: 10.1126/science.1218889

2. O'Connell, L., & Hofmann, H. (2011). The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis The Journal of Comparative Neurology, 519 (18), 3599-3639 DOI: 10.1002/cne.22735

3. O’Connell, L., & Hofmann, H. (2011). Genes, hormones, and circuits: An integrative approach to study the evolution of social behavior Frontiers in Neuroendocrinology, 32 (3), 320-335 DOI: 10.1016/j.yfrne.2010.12.004

The "Love Hormone" of 2012

Hello and welcome to the Love Hormone Pageant Results Show!  You have cast your votes, the results are in, and the “Love Hormone” of 2012 is… (dramatic pause)… Dopamine!

Dopamine is arguably the most exciting of love hormones. A neurotransmitter produced in the brain, dopamine plays a key role in many motivated behaviors (and love, especially falling in love, involves a lot of motivated behavior). It does this mostly through the mesolimbic reward system, which largely consists of dopamine-producing neuron cells in a brain region called the ventral tegmental area and their projections to other brain regions, including the nucleus accumbens. The mesolimbic reward system exists and has been studied in mammals, birds, reptiles and fish, but the story of how dopamine may be involved in “love” has been explored most with one particular mammal species, the prairie vole.

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

The prairie vole is a small rodent from the grasslands of the central United States. Unlike approximately 97% of mammal species, prairie voles are socially monogamous and form long-term pair bonds. Male and female pairs travel together, nest together and share parenting duties. Pairs tend to stay together for life and when one partner dies, the surviving partner may never re-pair with a new mate. The role that dopamine plays in how these pair bonds are formed between prairie vole couples has been studied extensively over the last 13 years by Zuoxin Wang at Florida State University and over 30 of his colleagues. Kimberly Young, Kyle Gobrogge, Yan Liu and Zuoxin Wang summarize much of this work in a recent review.

Graph showing that prairie voles prefer to
spend time with their partner after 24 hours
of living together and mating:fromYoung,
Gobrogge, Liu and Wang paper in
Frontiers in Neuroendocrinology (2011)

If you put a virgin male and a virgin female prairie vole in an enclosure and let them live together and mate for 24 hours, they will reliably prefer to spend time with each other rather than with a stranger if given that choice – this is called partner preference. If you enhance dopamine action in the brain, this partner preference will happen even sooner and if you block dopamine receptors throughout the brain, it won’t happen at all. This pattern is even true if you change dopamine action only in the nucleus accumbens, showing that dopamine binding in the nucleus accumbens is critical for the formation of partner preference and pair bonds.

The effect of a hormone or neurotransmitter is completely dependent on its receptors: where they are, how many there are, and how well things bind to them. Dopamine receptors can be classified into two main families, called D1-like and D2-like receptors, and they often have opposite effects. For example, in the prairie vole nucleus accumbens, activating D2 receptors or blocking D1 receptors will cause partner preference to form faster, whereas blocking D2 receptors or activating D1 receptors will prevent it from forming at all. Furthermore, male prairie voles develop more D1 receptors in the nucleus accumbens during pair bonding, which likely work to prevent the animal from forming a pair bond with a second female and keeping him faithful to his mate. Interestingly, promiscuous meadow voles generally have more D1-like receptors in the nucleus accumbens than closely related but monogamous prairie voles. So in the prairie vole nucleus accumbens, activation of D2 receptors promotes the formation of pair bonds and activation of D1 receptors prevents the formation of pair bonds.

However, dopamine is not all roses and chocolate hearts. The action of dopamine in the mesolimbic reward system, and especially in the nucleus accumbens, regulates much more than pair bonding; It regulates a whole suite of motivated social behaviors, like sexual, parental, play, and aggressive behaviors, as well as other motivated behaviors, like seeking food and drugs of addiction. Furthermore, mesolimbic dopamine seems to be at the heart of the interactions between drugs of abuse and social behavior. In another recent review by the same research group, Wang and his colleagues point out that brief exposure to any known drug of abuse activates dopamine activity in the nucleus accumbens and repeated drug exposure causes long-lasting or permanent changes to mesolimbic reward brain areas like the nucleus accumbens. For example, repeated exposure to psychostimulants increases the number and sensitivity of D1 receptors in the nucleus accumbens…Wait, what do active D1 receptors in the nucleus accumbens do? Oh yeah, they prevent pair bonding and partner preference formation. And not surprisingly, giving amphetamine (a psychostimulant) to prairie voles prevents them from forming partner preferences and pair bonds. So if you don’t want to hurt your chances of falling in love some day, just say “No” to drugs, mmmkay?

Dopamine is a busy neurohormone: It is not only involved in love and motivated behaviors, but is also involved in everything from voluntary movement, mood, punishment and reward, cognition, memory, learning, aggression, pain perception and sleep. It is also important to keep in mind that dopamine does not work alone. To regulate pair bonding and partner preference, dopamine interacts with oxytocin, vasopressin, glutamate, GABA, and corticotrophin-releasing factor. But then again, love is about as complex a brain function as you can get – we couldn’t expect a single hormone to go it alone!

So put your hands together one last time to celebrate the “Love Hormone” of 2012: Dopamine!

Want to know more? Check these out:

Young, K., Gobrogge, K., Liu, Y., & Wang, Z. (2011). The neurobiology of pair bonding: Insights from a socially monogamous rodent Frontiers in Neuroendocrinology, 32 (1), 53-69 DOI: 10.1016/j.yfrne.2010.07.006

Young, K., Gobrogge, K., & Wang, Z. (2011). The role of mesocorticolimbic dopamine in regulating interactions between drugs of abuse and social behavior Neuroscience & Biobehavioral Reviews, 35 (3), 498-515 DOI: 10.1016/j.neubiorev.2010.06.004

The Same Clay

According to a Hopi creation myth, the world was once nothing but water and dry land. The Sun, in his daily travels across the dry land, noticed that he had not seen a single living being. The Sun mentioned this observation to Hurúing Wuhti of the east and Hurúing Wuhti of the west, the deities of all hard substances, and they decided they would make a little bird. Hurúing Wuhti of the east made a wren out of clay and covered it with a piece of native cloth. The deities then sang a song over it and the wren came to life. They sent the wren to fly all over the earth to search for anything living, which it did. When the wren returned and reported that no living being existed anywhere, Hurúing Wuhti of the west shaped the clay to form all kinds of birds and placed these clay birds under the native cloth. The deities sang over the clay birds, bringing them to life, and they taught each of them what sounds they should make and sent them to populate the earth. Hurúing Wuhti of the west then shaped the clay to form all kinds of other animals and placed these clay animals under the native cloth. The deities sang over the clay animals, bringing them to life, and they taught them each what sounds they should make and sent them to populate the earth. Hurúing Wuhti of the east then shaped the clay to form a woman and a man and placed these people under the native cloth. The deities brought them to life with their song, and they taught them language and sent them to populate the earth.

I like this myth; in particular because it illustrates that despite the awesome diversity of the animals on our planet, we are all made of the same stuff and share many similarities. At first glance, we may be amazed by eels that resist eating prey fish who are providing a dental cleaning service (like the one on the left),

or by snakes that eat animals larger than their own heads and toads that save themselves from the jaws of death by puffing up their bodies even larger than the snake can handle (like the snake and toad battling it out on the right),

or by the elaborate displays of male birds in their attempts to woo females (like the golden pheasant below),

or by kangaroo moms that guard their toddler-like young in their own bodies (like the one on the right).

But at closer inspection, we realize that all of these animals are facing similar challenges: All animals are driven to eat and not be eaten, to stay healthy, to make babies, and to keep their babies alive. And animals have developed behavioral tools to achieve these goals, such as ways of finding or making food and a place to live, ways to defend these things, techniques for attracting the opposite sex, and parental methods. The details are extremely diverse across animal groups, but the ultimate goals and many of the strategies are common. And amazingly, the brain systems that regulate these behaviors are common too.

In a new synthesis of decades of research spanning the field of behavioral neuroscience, researchers Lauren O’Connell and Hans Hofmann from the University of Texas at Austin show that despite our impressive diversity, mammals, birds, reptiles, amphibians and fish are all molded from the same metaphorical clay. They specifically focus on two brain systems, often called the social behavior network and the mesolimbic reward system.

The social behavior network is a term first described in mammals by neuroscientist Sarah Newman to describe several brain regions that are all sensitive to steroid hormones (such as testosterone and estrogen), connect to each other, and are involved in many types of social behavior (including aggression, sexual behavior and parental behavior). We now know that reptiles, birds and fish also have brain areas that are similar in how they connect to one another and what neurotransmitters and other neurochemicals they use. More importantly, these brain areas seem to relate to the same types of social behaviors in similar ways.

The mesolimbic reward system is primarily a circuit of neurons that interact using the neurotransmitter dopamine. This neural circuit is central to how the brain controls motivation and a sense of desire and reward. This system is also involved in evaluating the importance of what is being perceived in order to behave accordingly. The mesolimbic reward system has been studied most in mammals, but birds, reptiles and fish are known to seek pleasure too and similar brain structures are likely involved.

This figure from O'Connell and Hofmann's paper in the Journal of Comparative Neurology shows corresponding brain regions in mammals, birds, reptiles, amphibians and fish. The images are shown as cross-sections of the brains as if we are looking directly at the front of the animals.

O’Connell and Hofmann show that the social behavior network and mesolimbic reward system work together as a single social decision-making system. For example, if one animal comes onto the territory of another animal, the brain areas of these two systems will work together to determine if the interloper should be fought, courted, nurtured, or eaten. (Imagine the consequences of getting this decision wrong!) Although mammals, birds, reptiles, amphibians and fish have very different lifestyles and brains, most of the brain areas of this social decision-making system are present, identifiable, and most importantly, play similar roles in regulating social behavior across all these animal groups. In the end, we’re not all so different after all.

Want to know more? Check these out:
1. O’Connell, L.A. and Hofmann, H.A. (2011). The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis. The Journal of Comparative Neurology, 519(18), 3599-3639.
2. O’Connell, L.A. and Hofmann, H.A. (2011). Genes, hormones, and circuits: An integrative approachto study the evolution of social behavior. Frontiers in Neuroendocrinology, 32, 320-335.
3. Native American legends at FirstPeople.us