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

Social butterflies or wallflowers? Two brain regions and a peptide

Zebra finches are really social little birds. When conditions are not right for breeding (usually when there’s not enough rain), they hang out in flocks of hundreds. And in the intimate mood the rain brings, groups break up into more manageable sizes of 10-20 birds, which still seems like a lot to me. Although, if you’re the type to have a “quiet night in” with just a dozen or so of your closest friends, you may be able to relate to the gregarious zebra finch. 

This is a zebra finch pair.
Photo by Keith Gerstung, Wikimedia commons.

This is not a flock of zebra finches, but it kinda looks like one. This is a flock
of chestnut-breasted munias, which is another Australian species of the
same family (Estrildidae). Photo by Duncan McCaskill, Wikimedia commons.

What makes some individuals more social than others? And what makes one individual change from being more social to less social (and vice versa)? One of the secrets to sociality in birds may lie in a neuropeptide called vasotocin. 

Vasotocin is a chemical messenger in the brains of birds, reptiles, amphibians and fishes (very similar to vasopressin in mammals) and it is known to be involved in several social behaviors. Researchers from Indiana University (including Aubrey Kelly, Marcy Kingsbury, Sara Schrock, David Kabelik and Jim Goodson) and Bowdoin College (Kristin Hoffbuhr, Brandon Waxman and Rick Thompson) got together to explore if and how vasotocin may be involved in how social zebra finches are. 

The top picture is a cartoon of a slice of
zebra finch brain, showing where BSTm
and LS are. The bottom image is a photo
of a brain section under the microscope.
Vasotocin is labeled in green. Figure from
Kelly, et al. (2011) Hormones and Behavior.

Chemical messengers, like vasotocin, generally don’t act equally on all parts of the brain, but rather have particular effects on specific brain regions. This is in part because certain chemicals are only produced by neurons (a type of brain cell) in some brain regions. Perhaps more importantly, the action of a chemical messenger is almost completely dependent on its receptors, and the receptors are also typically only located in specific brain regions. When you consider that neurons all project and talk to different areas of the brain, you can see that this system can get very complicated very quickly. Despite these complexities, this research team has narrowed in on two regions of the zebra finch brain that seem to be using vasotocin to regulate how social they are. 

The medial bed nucleus of the stria terminalis is a ridiculously long name for a brain region that is part of the extended amygdala (We’ll call it BSTm). Many neurons in the BSTm produce vasotocin (and are therefore called vasotocinergic neurons) and release the peptide in another brain area called the lateral septum (We’ll call it LS). The LS does not contain neurons that produce vasotocin (like the BSTm does), but instead contains neurons with vasotocin receptors, which vasotocin can bind to and take effect. 

Jim Goodson and another colleague, Yiwei Wang, had previously found that when zebra finches are allowed to socialize with other zebra finches, more of their vasotocinergic neurons in the BSTm become active. Could vasotocin produced in the BSTm and released in the LS underlie how social an animal is? 

If you were the zebra finch in the middle cage, which perch would you prefer to be on?
Figure from Kelly, et al. (2011) Hormones and Behavior paper.

One way to ask a zebra finch how social he’s feeling is to use a choice paradigm: that is, to put him in a cage with ten birds on one side, two birds on the other side, then see what side he hangs out on. The middle section (containing our bird of interest) contains a bunch of perches at different distances from the “flocks”. In this scenario, a zebra finch will sit on the perch next to the big flock on average 82% of the time, ‘cuz he’s social like that. But if the researcher injects a drug that blocks vasotocin receptors in the LS, he will sit on the perch next to the big flock on average 0% of the time. What do you think he does with all this free time? Typically, he sits on the perch next to the flock of two birds. So blocking vasotocin receptors in the LS seems to make zebra finches less social (but not asocial – If that were the case they would probably avoid both groups of birds). This suggests that more vasotocin binding to vasotocin receptors in the LS makes birds want to hang out with a large group. But, is the vasotocin that’s being released in this region and causing this behavior coming from the BSTm or another brain region? To figure this out, the researchers needed to look at (and experimentally alter) the vasotocin neurons in the BSTm.

Vasotocin is a peptide, and peptides are produced by a process in which the instructions for producing the peptide on the DNA is transcribed onto a molecule of messenger RNA. The instructions on the messenger RNA are then used to build the peptide. A drug called an antisense oligonucleotide can bind to that messenger RNA and confuse the instructions so the peptide doesn’t get made as much. This kind of drug was used to reduce the amount of vasotocin produced by BSTm neurons. 

Birds that had less vasotocin produced in the BSTm spent less time on the perch next to the large group, and spent more time on the perch next to the small group, compared to birds with natural vasotocin levels. They also explored less and took longer to feed if a strange object was in the cage, indicating that they were anxious. Together, it looks like vasotocin produced by neurons in the BSTm and acting on receptors in the LS may increase sociality and reduce anxiety (maybe social anxiety?) in gregarious birds like zebra finches. 

When you’re at a party, do you find yourself the life of the party or are you more comfortable hanging out in the corner with a few friends? Maybe you’re feeling more social at one party and less social at another? Could we have a system in our brain similar to the zebra finches? We have BST and LS brain regions and we have vasopressin, which is a lot like vasotocin. Hmmm… I guess this could be something to break the ice with at your next social mixer. 

Check out this zebra finch rockin’ out on electric guitar at a zebra finch party: 

Want to know more? Check these out:

1. Kelly, A., Kingsbury, M., Hoffbuhr, K., Schrock, S., Waxman, B., Kabelik, D., Thompson, R., & Goodson, J. (2011). Vasotocin neurons and septal V1a-like receptors potently modulate songbird flocking and responses to novelty Hormones and Behavior, 60 (1), 12-21 DOI: 10.1016/j.yhbeh.2011.01.012

2. Scientific American blogger Scicurious talks more about zebra finch brains here

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