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Testosterone, Aggression... Confusion

Breaking news from the BBC -

Testosterone link to aggression 'all in the mind'

Work in Nature magazine suggests the mind can win over hormones... Testosterone induces anti-social behaviour in humans, but only because of our own prejudices about its effect rather than its biological activity, suggest the authors.

The researchers, led by Ernst Fehr of the University of Zurich, Switzerland, said the results suggested a case of "mind over matter" with the brain overriding body chemistry.

"Whereas other animals may be predominantly under the influence of biological factors such as hormones, biology seems to exert less control over human behaviour," they said.

Phew, that's a relief - for a minute back there I was worried we didn't have free will. But look a little closer at the study, and it turns out that all is not as it seems. The experiment (Eisenegger et al) involved giving healthy women 0.5 mg testosterone, or placebo, in a randomized double-blind manner, and then getting them to take part in the "Ultimatum Game".

This is a game for two players. One, the Proposer, is given some money, and then has to offer to give a certain proportion of it to the other player, the Receiver. If the Receiver accepts the offer, both players get the agreed-upon amount of money. If they reject it, however, no-one gets anything.

The Proposer is basically faced with the choice of making a "fair" offer, e.g. giving away 50%, or a greedy one, say offering 10% and keeping 90% for themselves. Receivers generally accept fair offers, but most people get annoyed or insulted by unfair ones, and reject them, even though this means they lose money (10% of the money is still more than 0%).

What happened? Testosterone affected behaviour. It had no effect on women playing the role of the Receivers, but the Proposers given testosterone made significantly fairer offers on average, compared to those given placebo. That's not mind over matter, that's matter over mind - give someone a hormone and their behaviour changes.

The direction of the effect is quite interesting - if testosterone increased aggression, as popular belief has it, you might expect it to decrease fair offers. Or, you might not. I suppose it depends on your understanding of "aggression". For their part, Eisenegger et al interpret this finding as suggesting that testosterone doesn't increase aggression per se, but rather increases our motivation to achieve "status", which leads to Proposers making fairer offers, so as to appear nicer. Hmm. Maybe.

But where did the BBC get the whole "all in the mind" thing from? Well, after the testing was over, the authors asked the women whether they thought they had taken testosterone or placebo. The results showed that the women couldn't actually tell which they'd had - they were no more accurate than if they were guessing - but women who believed they'd got testosterone made more unfair offers than women who believed they got placebo. The size of this effect was bigger than the effect of testosterone.

Is that "mind over matter"? Do beliefs about testosterone exert a more powerful effect on behaviour than testosterone itself? Maybe they do, but these data don't tell us anything about that. The women's beliefs weren't manipulated in any way in this trial, so as an experiment it couldn't investigate belief effects. In order to show that belief alters behaviour, you'd need to control beliefs. You could randomly assign some subjects to be told they were taking testosterone, and compare them to others told they were on placebo, say.

This study didn't do anything like that. Beliefs about testosterone were only correlated with behaviour, and unless someone's changed the rules recently, correlation isn't causation. It's like finding that people with brown skin are more likely to be Hindus than people with white skin, and concluding that belief in Brahma alters pigmentation. It could even be that the behaviour drove the belief, because subjects were quizzed about their testosterone status after the Ultimatum Game - maybe women who, for whatever reason, behaved selfishly, decided that this meant they had taken testosterone!

Overall, this study provides quite interesting data about hormonal effects on behaviour, but tells us nothing about the effects of beliefs about hormones. On that issue, the way the media have covered this experiment is rather more informative than the experiment itself.

[BPSDB]

Eisenegger, C., Naef, M., Snozzi, R., Heinrichs, M., & Fehr, E. (2009). Prejudice and truth about the effect of testosterone on human bargaining behaviour Nature DOI: 10.1038/nature08711

Testosterone, Aggression... Confusion

Breaking news from the BBC -

Testosterone link to aggression 'all in the mind'

Work in Nature magazine suggests the mind can win over hormones... Testosterone induces anti-social behaviour in humans, but only because of our own prejudices about its effect rather than its biological activity, suggest the authors.

The researchers, led by Ernst Fehr of the University of Zurich, Switzerland, said the results suggested a case of "mind over matter" with the brain overriding body chemistry.

"Whereas other animals may be predominantly under the influence of biological factors such as hormones, biology seems to exert less control over human behaviour," they said.

Phew, that's a relief - for a minute back there I was worried we didn't have free will. But look a little closer at the study, and it turns out that all is not as it seems. The experiment (Eisenegger et al) involved giving healthy women 0.5 mg testosterone, or placebo, in a randomized double-blind manner, and then getting them to take part in the "Ultimatum Game".

This is a game for two players. One, the Proposer, is given some money, and then has to offer to give a certain proportion of it to the other player, the Receiver. If the Receiver accepts the offer, both players get the agreed-upon amount of money. If they reject it, however, no-one gets anything.

The Proposer is basically faced with the choice of making a "fair" offer, e.g. giving away 50%, or a greedy one, say offering 10% and keeping 90% for themselves. Receivers generally accept fair offers, but most people get annoyed or insulted by unfair ones, and reject them, even though this means they lose money (10% of the money is still more than 0%).

What happened? Testosterone affected behaviour. It had no effect on women playing the role of the Receivers, but the Proposers given testosterone made significantly fairer offers on average, compared to those given placebo. That's not mind over matter, that's matter over mind - give someone a hormone and their behaviour changes.

The direction of the effect is quite interesting - if testosterone increased aggression, as popular belief has it, you might expect it to decrease fair offers. Or, you might not. I suppose it depends on your understanding of "aggression". For their part, Eisenegger et al interpret this finding as suggesting that testosterone doesn't increase aggression per se, but rather increases our motivation to achieve "status", which leads to Proposers making fairer offers, so as to appear nicer. Hmm. Maybe.

But where did the BBC get the whole "all in the mind" thing from? Well, after the testing was over, the authors asked the women whether they thought they had taken testosterone or placebo. The results showed that the women couldn't actually tell which they'd had - they were no more accurate than if they were guessing - but women who believed they'd got testosterone made more unfair offers than women who believed they got placebo. The size of this effect was bigger than the effect of testosterone.

Is that "mind over matter"? Do beliefs about testosterone exert a more powerful effect on behaviour than testosterone itself? Maybe they do, but these data don't tell us anything about that. The women's beliefs weren't manipulated in any way in this trial, so as an experiment it couldn't investigate belief effects. In order to show that belief alters behaviour, you'd need to control beliefs. You could randomly assign some subjects to be told they were taking testosterone, and compare them to others told they were on placebo, say.

This study didn't do anything like that. Beliefs about testosterone were only correlated with behaviour, and unless someone's changed the rules recently, correlation isn't causation. It's like finding that people with brown skin are more likely to be Hindus than people with white skin, and concluding that belief in Brahma alters pigmentation. It could even be that the behaviour drove the belief, because subjects were quizzed about their testosterone status after the Ultimatum Game - maybe women who, for whatever reason, behaved selfishly, decided that this meant they had taken testosterone!

Overall, this study provides quite interesting data about hormonal effects on behaviour, but tells us nothing about the effects of beliefs about hormones. On that issue, the way the media have covered this experiment is rather more informative than the experiment itself.

[BPSDB]

Eisenegger, C., Naef, M., Snozzi, R., Heinrichs, M., & Fehr, E. (2009). Prejudice and truth about the effect of testosterone on human bargaining behaviour Nature DOI: 10.1038/nature08711

Good People

"Let anyone who comes to you go away feeling better and happier. Every one should see goodness in your face, in your eyes, in your smile." - Mother Teresa

Today we learned about Mother Teresa at school. We were talking about giving back to people who need your help. Mother Teresa is 1 of my favorite people to learn about. I like going to Catholic school a lot. We learn about a lot of important people. I know I wouldn't learn about them in regular school. My friends from dance class don't.

I'm asking my dad for a book about Mother Teresa for Christmas. I think it is important to learn about good people like her. I want to be a good person like. Someone who can make people smile. I want to make people happy.

My Nana does that. She takes the time to make sure we are all ok. I know that she works a lot. But she is never to busy for me. I wish that I had a mom. 1 like her. I like to spend time with her. Wednesdays are my favorite days. Because she picks me up from school. We go eat lunch and go to the library. Sometimes we go shopping too. But I like to just spend time with her. Because she makes me feel good and happy. I want to be like her when I get older. C

Memories Glow Under the Microscope

How does memory work? What changes in the brain when we learn something?


We don't know for sure. But two outstanding Nature papers have just provided an important piece of the puzzle, using a truly amazing technique which allowed them to examine the brain of a living, breathing mouse under the microscope.

The approach uses mice genetically engineered such that some of their neurons contain yellow fluorescent protein (YFP). You may have already heard of the cute glowing mice who have green fluorescent protein (GFP) in all their cells. In these YFP-H mice, only some of their neurons are fluorescent.

Two-photon microscopy uses a focused laser beam to image fluorescent tissue. The authors of these papers were able to image the brain (the cortex) after surgically thinning - but not penetrating - the mice's skulls. The bone over the brain area in question was removed until it was just 20 micrometers thick. The brain itself was not interfered with in any way, which is what makes this method so remarkable. Generally, when you put a brain under a microscope, you've had to cut slices off it first.

*

Using this transcranial two-photon microscopy, these two teams of researchers (Xu et al from Santa Cruz and Yang et al from New York) were able to directly observe the neural changes that took place following motor skill learning. Adolescent and adult mice were trained on a difficult movement task, such as the "rotarod", in which the animal has to avoid falling off a constantly rotating metal rod. With a few day's practice, most of the mouse got better at the tasks.

Both of the papers report that the skill learning was associated with the formation of new dendritic spines in the motor cortex. The image below shows the kind of data we're talking about: this is a single neuron, and the little blobs above and below it are individual dendritic spines, or outgrowths, of the cell. The top image shows the cell before training, and the bottom image is the same cell 24 hours later, after skill learning. Several new dendritic spines have grown. Almost certainly, these spines have formed synapses with another cell.

The results of these studies show that training increases the amount of new dendritic spine formation in the motor cortex, compared to control conditions in which there is no skill learning, and that many of the new spines persist for months. Learning also seems to be associated with the removal of some already existing spines, so the overall number of spines in the brain remains roughly constant.

Overall, this is a pretty amazing set of results, and it suggests that the learning of new skills is associated not only with changes in the "strength" of existing synapses between neurons, but actually with the growth of entirely new synapses. New brain cells are not generated in the adult brain except in a couple of very specific areas, but it seems that experience causes the reshaping of existing cells.

There are lots of unanswered questions - such as whether the same process underlies other forms of learning as well as motor skill training, what triggers the formation of new dendritic spines, and how the process works in humans. But this is a very exciting first step.



Xu, T., Yu, X., Perlik, A., Tobin, W., Zweig, J., Tennant, K., Jones, T., & Zuo, Y. (2009). Rapid formation and selective stabilization of synapses for enduring motor memories Nature DOI: 10.1038/nature08389

Yang, G., Pan, F., & Gan, W. (2009). Stably maintained dendritic spines are associated with lifelong memories Nature DOI: 10.1038/nature08577

Memories Glow Under the Microscope

How does memory work? What changes in the brain when we learn something?


We don't know for sure. But two outstanding Nature papers have just provided an important piece of the puzzle, using a truly amazing technique which allowed them to examine the brain of a living, breathing mouse under the microscope.

The approach uses mice genetically engineered such that some of their neurons contain yellow fluorescent protein (YFP). You may have already heard of the cute glowing mice who have green fluorescent protein (GFP) in all their cells. In these YFP-H mice, only some of their neurons are fluorescent.

Two-photon microscopy uses a focused laser beam to image fluorescent tissue. The authors of these papers were able to image the brain (the cortex) after surgically thinning - but not penetrating - the mice's skulls. The bone over the brain area in question was removed until it was just 20 micrometers thick. The brain itself was not interfered with in any way, which is what makes this method so remarkable. Generally, when you put a brain under a microscope, you've had to cut slices off it first.

*

Using this transcranial two-photon microscopy, these two teams of researchers (Xu et al from Santa Cruz and Yang et al from New York) were able to directly observe the neural changes that took place following motor skill learning. Adolescent and adult mice were trained on a difficult movement task, such as the "rotarod", in which the animal has to avoid falling off a constantly rotating metal rod. With a few day's practice, most of the mouse got better at the tasks.

Both of the papers report that the skill learning was associated with the formation of new dendritic spines in the motor cortex. The image below shows the kind of data we're talking about: this is a single neuron, and the little blobs above and below it are individual dendritic spines, or outgrowths, of the cell. The top image shows the cell before training, and the bottom image is the same cell 24 hours later, after skill learning. Several new dendritic spines have grown. Almost certainly, these spines have formed synapses with another cell.

The results of these studies show that training increases the amount of new dendritic spine formation in the motor cortex, compared to control conditions in which there is no skill learning, and that many of the new spines persist for months. Learning also seems to be associated with the removal of some already existing spines, so the overall number of spines in the brain remains roughly constant.

Overall, this is a pretty amazing set of results, and it suggests that the learning of new skills is associated not only with changes in the "strength" of existing synapses between neurons, but actually with the growth of entirely new synapses. New brain cells are not generated in the adult brain except in a couple of very specific areas, but it seems that experience causes the reshaping of existing cells.

There are lots of unanswered questions - such as whether the same process underlies other forms of learning as well as motor skill training, what triggers the formation of new dendritic spines, and how the process works in humans. But this is a very exciting first step.



Xu, T., Yu, X., Perlik, A., Tobin, W., Zweig, J., Tennant, K., Jones, T., & Zuo, Y. (2009). Rapid formation and selective stabilization of synapses for enduring motor memories Nature DOI: 10.1038/nature08389

Yang, G., Pan, F., & Gan, W. (2009). Stably maintained dendritic spines are associated with lifelong memories Nature DOI: 10.1038/nature08577

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