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Scientists believe that most behaviors, from fighting to mating, are controlled by brain chemistry. In this Science Update, you’ll hear how researchers are using hamsters to understand the roots of aggression.
Is aggression a matter of chemistry? I'm Bob Hirshon and this is Science Update.
Studying how brain chemistry affects aggression is pretty much impossible to do with people. So scientists like Elliott Albers at Georgia State University and the Center for Behavioral Neuroscience in Atlanta turn to the Syrian gold hamster.
One of the reasons it’s an interesting model is because it’s rather a nonsocial animal. From what we know about these animals is that they do not like to be with other Syrian hamsters.
In fact, two hamsters placed together will quickly start fighting to establish which one is dominant. They then mark up the cage with scent. And somehow, this scent tells the world who’s the top hamster, so they don’t have to keep fighting.
The researchers have found that a single chemical, vasopressin, will induce the hamsters to engage in this scent marking. Another chemical that inhibits vasopressin stops it.
So, it’s almost as if we found a trigger or a switch for this behavior. And as far as I know, this is the best example of a single neurochemical substance injected into a specific area of the brain that will induce a whole, complicated behavior in a mammal.
And while hamsters are quite different than people, understanding how hormones affect them could one day provide insights into human behavior as well. For the American Association for the Advancement Of Science, I'm Bob Hirshon.
Making Sense of the Research
Scientists are very interested in the biology and chemistry of human beings. Unfortunately, our minds, bodies, and behaviors are very complex, so in many cases it’s easier to start by looking at a simpler model. For example, Gregor Mendel, the father of modern genetics, made some of his groundbreaking discoveries by studying pea plants. Today, neuroscientists often study nerve cells from leeches, because the nerves are big and easy to manipulate.
To study social behavior, Albers and his colleagues have chosen an animal with a very simple social life: the Syrian hamster. These hamsters don’t have close friends. They don’t travel in groups. They don’t socialize with their extended families. They basically come together only to mate or to fight. So, the researchers can study the fighting behavior in its own right without keeping track of too many complicating factors.
Still, Albers says it was surprising that a single chemical signal – vasopressin – had such a profound influence on the hamsters’ behavior. When it was injected into a certain part of the brain, the hamsters would spend about ten minutes doing nothing but scent-marking. When a chemical that blocked vasopressin was injected in the same way, the hamsters wouldn’t scent-mark at all, even in situations where they normally would.
Scent-marking is important because it maintains a certain level of peace among the hamsters. It’s very important for two hamsters to know which one of them is dominant – in other words, which one has control of the territory. When two hamsters meet and don’t know each other, they fight until one of them wins and establishes dominance. But after that, the scent-marking reminds them who’s boss. It may sound a little oppressive, but at least it keeps them from fighting over and over again.
Although the results of the experiment were very straightforward, this is hardly the end of the story, even for the hamsters. The researchers have already found out that another hormone, testosterone, can alter the number of cells in the brain that respond to vasopressin. As a result, changes in testosterone levels can make the animals either more or less sensitive to vasopressin. And hormones like vasopressin and testosterone are involved in other behaviors, including mating, so their role even in hamster behavior is probably very complex. In humans, it’s certainly much more so. Still, understanding how certain hormones and chemicals may affect behavior could lead to better treatments for behavior problems in people.
Now try and answer these questions:
- Why is the Syrian hamster a useful model of social behavior?
- What is the relationship between scent-marking and aggression?
- How does the hormone vasopression affect the scent-marking behavior?
- Can you think of behaviors in humans that establish “dominance” without provoking a fight?
- If a drug could be developed that suppressed aggression in humans, do you think it should be used? Under what circumstances? What are the potential benefits and drawbacks of using chemicals to modify behavior?
Neuroscience for Kids contains a collection of activities for teachers and students who want to learn more about the nervous system.
For one student’s perspective on the source of aggression, read Can the Source of Aggression be found in the Brain? , an essay on Serendip, a forum sponsored by Bryn Mawr College.
To read about the effects that chocolate and nicotine have on the brain, see: