Deep Brain Stimulation Cures Urge To Break Glass

Deep Brain Stimulation (DBS) is in. There's been much buzz about its use in severe depression, and it has a long if less glamorous record of success in Parkinson's disease. Now that it's achieved momentum as a treatment in psychiatry, DBS is being tried in a range of conditions including chronic pain, obsessive-compulsive disorder and Tourette's Syndrome. Is the hype justified? Yes - but the scientific and ethical issues are more complex, and more interesting, than you might think.

Biological Psychiatry have just published this report of DBS in a man who suffered from severe, untreatable Tourette's syndrome, as well as OCD. The work was performed by a German group, Neuner et. al. (who also have a review paper just out), and they followed the patient up for three years after implanting high-frequency stimulation electrodes in an area of the brain called the nucleus accumbens. It's fascinating reading, if only for the insight into the lives of the patients who receive this treatment.

The patient suffered from the effects of auto-aggressive behavior such as self-mutilation of the lips, forehead, and fingers, coupled with the urge to break glass. He was no longer able to travel by car because he had broken the windshield of his vehicle from the inside on several occasions.

It makes even more fascinating viewing, because the researchers helpfully provide video clips of the patient before and after the procedure. Neuropsychiatric research meets YouTube - truly, we've entered the 21st century. Anyway, the DBS seemed to work wonders:

... An impressive development was the cessation of the self-mutilation episodes and the urge to destroy glass. No medication was being used ... Also worthy of note is the fact that the patient stopped smoking during the 6 months after surgery. In the follow-up period, he has successfully refrained from smoking. He reports that he has no desire to smoke and that it takes him no effort to refrain from doing so.

Impressive indeed. DBS is, beyond a doubt, an exciting technology from both a theoretical and a clinical perspective. Yet it's worth considering some things that tend to get overlooked.

Firstly, although DBS has a reputation as a high-tech, science-driven, precisely-targeted treatment, it's surprisingly hit-and-miss. This report involved stimulation of the nucleus accumbens, an area best known to neuroscientists as being involved in responses to recreational drugs. (It's tempting to infer that this must have something to do with why the patient quit smoking.) I'm sure there are good reasons to think that DBS in the nucleus accumbens would help with Tourette's - but there are equally good reasons to target several other locations. As the authors write:

For DBS in Tourette's patients, the globus pallidus internus (posteroventrolateral part, anteromedial part), the thalamus (centromedian nucleus, substantia periventricularis, and nucleus ventro-oralis internus) and the nucleus accumbens/anterior limb of the internal capsule have all been used as target points.

For those whose neuroanatomy is a little rusty, that's a fairly eclectic assortment of different brain regions. Likewise, in depression, the best-known DBS target is the subgenual cingulate cortex, but successful cases have been reported with stimulation in two entirely different areas, and at least two more have been proposed as potential targets (Paper.) Indeed, even once a location for DBS has been chosen, it's often necessary to try stimulating at several points in order to find the best target. The point is that there is no "Depression center" or "Tourette's center" in the brain which science has mapped out and which surgery can now fix.

Second, by conventional standards, this was an awful study: it only had one patient, no controls, and no blinding. Of course, applying usual scientific standards to this kind of research is all but impossible, for ethical reasons. These are people, not lab rats. And it does seem unlikely that the dramatic and sustained response in this case could be purely the placebo effect, especially given that the patient had tried several medications previously.

So what the authors did was certainly reasonable under the circumstances - but still, this article, published in a leading journal, is basically an anecdote. If it had been about a Reiki master waving his hands at the patient, instead of a neurosurgeon sticking electrodes into him, it wouldn't even make it into the Journal of Alternative and Complementary Medicine. This is par for the course in this field; there have been controlled trials of DBS, but they are few and very small. Is this a problem? It would be silly to pretend that it wasn't - there is no substitute for good science. There's not much we can do about it, though.

Finally, Deep Brain Stimulation is a misleading term - the brain doesn't really get stimulated at all. The electrical pulses used in most DBS are at such a high frequency (145 Hz in this case) that they "overload" nearby neurons and essentially switch them off. (At least that's the leading theory.) In effect, turning on a DBS electrode is like cutting a hole in the brain. Of course, the difference is that you can switch off the electrode and put it back to normal. But this aside, DBS is little more sophisticated than the notorious "psychosurgery" pioneered by Walter Freeman performed back in the 1930s and that have since become so unpopular. I see nothing wrong with that - if it works, it works, and psychosurgery worked for many people, which is why it's still used in Britain today. It's interesting, though, that whereas psychosurgery is seen as the height of psychiatry barbarity, DBS is lauded as medical science at its most sophisticated.

For all that, DBS is the most interesting thing in neuroscience at the moment. Almost all research on the human brain is correlational - we look for areas of the brain which activate on fMRI scans when people are doing something. DBS offers one of the very few ways of investigating what happens when you manipulate different parts of the human brain. For a scientist, it's a dream come true. But of course, the only real reason to do DBS is for the patients. DBS promises to help people who are suffering terribly. If it does, that's reason enough to be interested in it.

See also: Someone with Parkinson's disease writes of his experiences with DBS on his blog.


I NEUNER, K PODOLL, D LENARTZ, V STURM, F SCHNEIDER (2008). Deep Brain Stimulation in the Nucleus Accumbens for Intractable Tourette's Syndrome: Follow-Up Report of 36 Months Biological Psychiatry DOI: 10.1016/j.biopsych.2008.09.030

Deep Brain Stimulation Cures Urge To Break Glass

Deep Brain Stimulation (DBS) is in. There's been much buzz about its use in severe depression, and it has a long if less glamorous record of success in Parkinson's disease. Now that it's achieved momentum as a treatment in psychiatry, DBS is being tried in a range of conditions including chronic pain, obsessive-compulsive disorder and Tourette's Syndrome. Is the hype justified? Yes - but the scientific and ethical issues are more complex, and more interesting, than you might think.

Biological Psychiatry have just published this report of DBS in a man who suffered from severe, untreatable Tourette's syndrome, as well as OCD. The work was performed by a German group, Neuner et. al. (who also have a review paper just out), and they followed the patient up for three years after implanting high-frequency stimulation electrodes in an area of the brain called the nucleus accumbens. It's fascinating reading, if only for the insight into the lives of the patients who receive this treatment.

The patient suffered from the effects of auto-aggressive behavior such as self-mutilation of the lips, forehead, and fingers, coupled with the urge to break glass. He was no longer able to travel by car because he had broken the windshield of his vehicle from the inside on several occasions.

It makes even more fascinating viewing, because the researchers helpfully provide video clips of the patient before and after the procedure. Neuropsychiatric research meets YouTube - truly, we've entered the 21st century. Anyway, the DBS seemed to work wonders:

... An impressive development was the cessation of the self-mutilation episodes and the urge to destroy glass. No medication was being used ... Also worthy of note is the fact that the patient stopped smoking during the 6 months after surgery. In the follow-up period, he has successfully refrained from smoking. He reports that he has no desire to smoke and that it takes him no effort to refrain from doing so.

Impressive indeed. DBS is, beyond a doubt, an exciting technology from both a theoretical and a clinical perspective. Yet it's worth considering some things that tend to get overlooked.

Firstly, although DBS has a reputation as a high-tech, science-driven, precisely-targeted treatment, it's surprisingly hit-and-miss. This report involved stimulation of the nucleus accumbens, an area best known to neuroscientists as being involved in responses to recreational drugs. (It's tempting to infer that this must have something to do with why the patient quit smoking.) I'm sure there are good reasons to think that DBS in the nucleus accumbens would help with Tourette's - but there are equally good reasons to target several other locations. As the authors write:

For DBS in Tourette's patients, the globus pallidus internus (posteroventrolateral part, anteromedial part), the thalamus (centromedian nucleus, substantia periventricularis, and nucleus ventro-oralis internus) and the nucleus accumbens/anterior limb of the internal capsule have all been used as target points.

For those whose neuroanatomy is a little rusty, that's a fairly eclectic assortment of different brain regions. Likewise, in depression, the best-known DBS target is the subgenual cingulate cortex, but successful cases have been reported with stimulation in two entirely different areas, and at least two more have been proposed as potential targets (Paper.) Indeed, even once a location for DBS has been chosen, it's often necessary to try stimulating at several points in order to find the best target. The point is that there is no "Depression center" or "Tourette's center" in the brain which science has mapped out and which surgery can now fix.

Second, by conventional standards, this was an awful study: it only had one patient, no controls, and no blinding. Of course, applying usual scientific standards to this kind of research is all but impossible, for ethical reasons. These are people, not lab rats. And it does seem unlikely that the dramatic and sustained response in this case could be purely the placebo effect, especially given that the patient had tried several medications previously.

So what the authors did was certainly reasonable under the circumstances - but still, this article, published in a leading journal, is basically an anecdote. If it had been about a Reiki master waving his hands at the patient, instead of a neurosurgeon sticking electrodes into him, it wouldn't even make it into the Journal of Alternative and Complementary Medicine. This is par for the course in this field; there have been controlled trials of DBS, but they are few and very small. Is this a problem? It would be silly to pretend that it wasn't - there is no substitute for good science. There's not much we can do about it, though.

Finally, Deep Brain Stimulation is a misleading term - the brain doesn't really get stimulated at all. The electrical pulses used in most DBS are at such a high frequency (145 Hz in this case) that they "overload" nearby neurons and essentially switch them off. (At least that's the leading theory.) In effect, turning on a DBS electrode is like cutting a hole in the brain. Of course, the difference is that you can switch off the electrode and put it back to normal. But this aside, DBS is little more sophisticated than the notorious "psychosurgery" pioneered by Walter Freeman performed back in the 1930s and that have since become so unpopular. I see nothing wrong with that - if it works, it works, and psychosurgery worked for many people, which is why it's still used in Britain today. It's interesting, though, that whereas psychosurgery is seen as the height of psychiatry barbarity, DBS is lauded as medical science at its most sophisticated.

For all that, DBS is the most interesting thing in neuroscience at the moment. Almost all research on the human brain is correlational - we look for areas of the brain which activate on fMRI scans when people are doing something. DBS offers one of the very few ways of investigating what happens when you manipulate different parts of the human brain. For a scientist, it's a dream come true. But of course, the only real reason to do DBS is for the patients. DBS promises to help people who are suffering terribly. If it does, that's reason enough to be interested in it.

See also: Someone with Parkinson's disease writes of his experiences with DBS on his blog.


I NEUNER, K PODOLL, D LENARTZ, V STURM, F SCHNEIDER (2008). Deep Brain Stimulation in the Nucleus Accumbens for Intractable Tourette's Syndrome: Follow-Up Report of 36 Months Biological Psychiatry DOI: 10.1016/j.biopsych.2008.09.030

Kruger & Dunning Revisited

The irreplaceable Overcoming Bias have an excellent post on every blogger's favorite psychology paper, Kruger and Dunning (1999) "Unskilled and Unaware Of It".

Most people (myself included) have taken this paper as evidence that the better you are at something, the better you are at knowing how good you are at it. Thus, people who are bad don't know that they are, which is why they don't try to improve. It's an appealing conclusion, and also a very intuitive one.

In general, these kind of conclusions should be taken with a pinch of salt.

Indeed, it turns out that there's another more recent paper, Burson et. al. (2006) "Skilled or Unskilled, but Still Unaware of It", which finds that everyone is pretty bad at judging their own skill, and in some circumstances, more skilled people make less accurate judgments than novices. Heh.

Kruger & Dunning Revisited

The irreplaceable Overcoming Bias have an excellent post on every blogger's favorite psychology paper, Kruger and Dunning (1999) "Unskilled and Unaware Of It".

Most people (myself included) have taken this paper as evidence that the better you are at something, the better you are at knowing how good you are at it. Thus, people who are bad don't know that they are, which is why they don't try to improve. It's an appealing conclusion, and also a very intuitive one.

In general, these kind of conclusions should be taken with a pinch of salt.

Indeed, it turns out that there's another more recent paper, Burson et. al. (2006) "Skilled or Unskilled, but Still Unaware of It", which finds that everyone is pretty bad at judging their own skill, and in some circumstances, more skilled people make less accurate judgments than novices. Heh.

Prozac Made My Cells Spiky

A great many neuroscientists are interested in clinical depression and antidepressants. We're still a long way from understanding depression on a biological level - and if anyone tries to tell you otherwise, they're probably trying to sell you something. I've previously discussed the controversies surrounding the neurotransmitter serotonin - according to popular belief, the brain's "happy chemical". My conclusion was that although clinical depression is not caused by "low serotonin" alone, serotonin does play an important role in mood at least in some people.

A paper published recently in Molecular Psychiatry makes a number of important contributions to the literature on depression and antidepressants; I haven't seen it discussed elsewhere, so here is make take on it. The paper is by a Portuguese research group, Bessa et. al., and it's titled The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling. The findings are right there in the title, but a little history is required in order to appreciate their significance.

For a long time, the only biological theory which attempted to explain clinical depression and how antidepressants counteract it was the monoamine hypothesis. During the early 1960s, it was noticed that early antidepressant drugs, such as imipramine, all inhibited either the breakdown or the removal (reuptake) of chemicals in the brain called monoamines, including serotonin. This led many to conclude that antidepressants improve mood by raising monoamine levels, and that depression is probably caused by some kind of monoamine deficiency. For various reasons (not all of them good ones), it was later decided that serotonin was the crucial monoamine involved in mood, although for several years another, noradrenaline, was favored by most people.

This "monoamine hypothesis" was always a little shaky, and over the past decade or so, an alternative approach has become increasingly fashionable. If you were so inclined, you might even call it a new paradigm. This is the proposal that antidepressants work by promoting the survival and proliferation of new neurones in certain areas of the brain - the "neurogenesis hypothesis". Neurogenesis, the birth of new cells from stem cells, occurs in a couple of very specific regions of the adult brain, including the elaborately named subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus. Many experiments on animals have shown that chronic stress, and injections of the "stress hormone" corticosterone, can suppress neurogenesis, while a wide range of antidepressants block this effect of stress and promote neurogenesis. (Other evidence shows that antidepressants probably do this by inducing the expression of neurotrophic signaling proteins, like BDNF.)

The literature on stress, neurogenesis, and antidepressants, is impressive and growing rapidly. For good reviews, see Duman (2004) and Duman & Monteggia (2006). However, the crucial question - do antidepressants work by boosting hippocampal neurogenesis? - remains a controversial one. The hippocampus is not an area generally thought of as being involved in mood or emotion, and damage to the human hippocampus causes amnesia, not depression. Given that the purpose (if any) of adult neurogenesis remains a mystery, it's entirely possible that neurogenesis has nothing to do with depression and mood.

To establish whether neurogenesis is involved in antidepressant action, you need to to manipulate it - for example, by blocking neurogenesis and seeing if this makes antidepressants ineffective. This is practically quite tricky, but Luca Santarelli et. al. (2003) managed to do it by irradiating the hippocampi of mice with x-rays. They found that this made two antidepressants (fluoxetine, aka Prozac, and imipramine) ineffective in protecting the animals against the detrimental effects of chronic stress. This was a landmark result, and raised a lot of interest in the neurogenesis theory.

This new paper, however, says differently. The authors gave lab rats a six-week Chronic Mild Stress treatment, a Guantanamo Bay-style program of intermittent food deprivation, sleep disruption, and confinement. Chronic stress has various effects on rats, including increased anxiety and decreased time spent grooming leading to fur deterioration. These behaviours and others can be quantified, and are treated as a rat analogue of human clinical depression - whether this is valid is obviously debatable, but I'm willing to accept it at least until a better animal model comes along.

Anyway, some of the rats were injected with antidepressants during the final two weeks of the stress procedure. As expected, these rats coped better with the stress at the end of six weeks. This graph shows the effects of stress and antidepressants on the rat's behaviour in the Forced Swim (Porsolt) Test. Higher bars indicate more "depressed" behaviour. The second pair of bars, representing the stressed rats who got placebo injections, is a lot higher than the first pair of bars representing rats who were not subjected to any stress. In other words, stress made rats "depressed" - no surprise. The other four pairs of bars are pretty much the same height as the first pair; these are rats who got antidepressants, showing that they were resistant to the effects of stress.

The crucial finding is that the white and the black bars are all pretty much the same height. The black bars represent animals who were given injections of methylazoxymethanol (MAM), a cytostatic toxin which blocks cell division (rather like cancer chemotherapy). As you can see, MAM had no effect at all on behaviour in the swim test. It had no effect on most other tests, although it did seem to make the rats more anxious in one experiment.

However, MAM powerfully inhibited neurogenesis. This second graph shows the number of hippocampal cells expressing KI-67, a protein which is a marker of neuroproliferation. As expected, stress reduced neurogenesis and antidepressants increased it. MAM (black bars again) reduced neurogenesis, and in particular, it completely blocked the ability of antidepressants to increase it.

But as we saw earlier, MAM did not stop antidepressants from protecting rats against stress. So, the authors concluded, neurogenesis is not necessary for antidepressants to work. This contradicts the landmark finding of Santarelli et. al. - why the discrepency? There are so many differences between the two experiments that there could be any number of explanations - the current study used rats, while Santarelli used mice, for one thing, and that could well be important. Whatever the reason, this result suggests at the least that neurogenesis is not the only mechanism by which antidepressants counteract the effects of stress in animals.

The most interesting aspect of this paper, to my mind, was an essentially unrelated new finding. Stress was found to reduce the volume of several areas of the rat's brain, including the hippocampus and also the medial prefrontal cortex (mPFC). Unlike the hippocampus, this is an area known to be involved in motivation and emotion. Importantly, the authors found that following stress, the mPFC did not shrink because neurones were dying or because fewer neurones were being born, but rather because the existing neurones were changing shape - stress caused atrophy of the dendritic spines which branch out from neurones. Dendrites are essential for communication between neurones.

As you can see in the drawings above, stress (the middle column) caused shrinking and stunting of the dendrites in pyrimidal neurones from three areas relative to the unstressed rats (left), while those rats recieving antidepressants as well as stress showed no such effect (right). The cytostatic MAM had no effect whatsoever on dendrites. Further work found that antidepressants increase expression of NCAM1, a protein which is involved in dendritic growth.

So what does this mean? Well, for one thing, it doesn't prove that antidepressants work by increasing dendritic branching. Cheekily, the authors come close to implying this in their choice of title for the paper, but the published evidence shows no direct evidence for this. To find out, you would have to show that blocking the effects of antidepressants on dendrites also blocks their beneficial effects. I suspect this is what the authors are now working hard to try to do, but they haven't done so yet.

It also doesn't mean that taking Prozac will change the shape of your brain cells. It might well do, but this was a study in rats given huge doses of antidepressants (by human standards), so we really don't know whether the findings apply to humans. On the other hand, if Prozac changes the shape of your cells, this study suggests that stressful situations do too - and Prozac, if anything, will put your cells back to "normal".

Finally, I don't want to suggest that the neurogenesis theory of depression is now "dead". In neuroscience, theories never live or die on the basis of single experiments (unlike in physics). But it does suggest that the much-blogged-about neurogenesis hypothesis is not the whole story. Depression isn't just a case of too little serotonin, and it isn't just a case of too little neurogenesis or too little BDNF either.


J M Bessa, D Ferreira, I Melo, F Marques, J J Cerqueira, J A Palha, O F X Almeida, N Sousa (2008). The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling Molecular Psychiatry DOI: 10.1038/mp.2008.119

Prozac Made My Cells Spiky

A great many neuroscientists are interested in clinical depression and antidepressants. We're still a long way from understanding depression on a biological level - and if anyone tries to tell you otherwise, they're probably trying to sell you something. I've previously discussed the controversies surrounding the neurotransmitter serotonin - according to popular belief, the brain's "happy chemical". My conclusion was that although clinical depression is not caused by "low serotonin" alone, serotonin does play an important role in mood at least in some people.

A paper published recently in Molecular Psychiatry makes a number of important contributions to the literature on depression and antidepressants; I haven't seen it discussed elsewhere, so here is make take on it. The paper is by a Portuguese research group, Bessa et. al., and it's titled The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling. The findings are right there in the title, but a little history is required in order to appreciate their significance.

For a long time, the only biological theory which attempted to explain clinical depression and how antidepressants counteract it was the monoamine hypothesis. During the early 1960s, it was noticed that early antidepressant drugs, such as imipramine, all inhibited either the breakdown or the removal (reuptake) of chemicals in the brain called monoamines, including serotonin. This led many to conclude that antidepressants improve mood by raising monoamine levels, and that depression is probably caused by some kind of monoamine deficiency. For various reasons (not all of them good ones), it was later decided that serotonin was the crucial monoamine involved in mood, although for several years another, noradrenaline, was favored by most people.

This "monoamine hypothesis" was always a little shaky, and over the past decade or so, an alternative approach has become increasingly fashionable. If you were so inclined, you might even call it a new paradigm. This is the proposal that antidepressants work by promoting the survival and proliferation of new neurones in certain areas of the brain - the "neurogenesis hypothesis". Neurogenesis, the birth of new cells from stem cells, occurs in a couple of very specific regions of the adult brain, including the elaborately named subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus. Many experiments on animals have shown that chronic stress, and injections of the "stress hormone" corticosterone, can suppress neurogenesis, while a wide range of antidepressants block this effect of stress and promote neurogenesis. (Other evidence shows that antidepressants probably do this by inducing the expression of neurotrophic signaling proteins, like BDNF.)

The literature on stress, neurogenesis, and antidepressants, is impressive and growing rapidly. For good reviews, see Duman (2004) and Duman & Monteggia (2006). However, the crucial question - do antidepressants work by boosting hippocampal neurogenesis? - remains a controversial one. The hippocampus is not an area generally thought of as being involved in mood or emotion, and damage to the human hippocampus causes amnesia, not depression. Given that the purpose (if any) of adult neurogenesis remains a mystery, it's entirely possible that neurogenesis has nothing to do with depression and mood.

To establish whether neurogenesis is involved in antidepressant action, you need to to manipulate it - for example, by blocking neurogenesis and seeing if this makes antidepressants ineffective. This is practically quite tricky, but Luca Santarelli et. al. (2003) managed to do it by irradiating the hippocampi of mice with x-rays. They found that this made two antidepressants (fluoxetine, aka Prozac, and imipramine) ineffective in protecting the animals against the detrimental effects of chronic stress. This was a landmark result, and raised a lot of interest in the neurogenesis theory.

This new paper, however, says differently. The authors gave lab rats a six-week Chronic Mild Stress treatment, a Guantanamo Bay-style program of intermittent food deprivation, sleep disruption, and confinement. Chronic stress has various effects on rats, including increased anxiety and decreased time spent grooming leading to fur deterioration. These behaviours and others can be quantified, and are treated as a rat analogue of human clinical depression - whether this is valid is obviously debatable, but I'm willing to accept it at least until a better animal model comes along.

Anyway, some of the rats were injected with antidepressants during the final two weeks of the stress procedure. As expected, these rats coped better with the stress at the end of six weeks. This graph shows the effects of stress and antidepressants on the rat's behaviour in the Forced Swim (Porsolt) Test. Higher bars indicate more "depressed" behaviour. The second pair of bars, representing the stressed rats who got placebo injections, is a lot higher than the first pair of bars representing rats who were not subjected to any stress. In other words, stress made rats "depressed" - no surprise. The other four pairs of bars are pretty much the same height as the first pair; these are rats who got antidepressants, showing that they were resistant to the effects of stress.

The crucial finding is that the white and the black bars are all pretty much the same height. The black bars represent animals who were given injections of methylazoxymethanol (MAM), a cytostatic toxin which blocks cell division (rather like cancer chemotherapy). As you can see, MAM had no effect at all on behaviour in the swim test. It had no effect on most other tests, although it did seem to make the rats more anxious in one experiment.

However, MAM powerfully inhibited neurogenesis. This second graph shows the number of hippocampal cells expressing KI-67, a protein which is a marker of neuroproliferation. As expected, stress reduced neurogenesis and antidepressants increased it. MAM (black bars again) reduced neurogenesis, and in particular, it completely blocked the ability of antidepressants to increase it.

But as we saw earlier, MAM did not stop antidepressants from protecting rats against stress. So, the authors concluded, neurogenesis is not necessary for antidepressants to work. This contradicts the landmark finding of Santarelli et. al. - why the discrepency? There are so many differences between the two experiments that there could be any number of explanations - the current study used rats, while Santarelli used mice, for one thing, and that could well be important. Whatever the reason, this result suggests at the least that neurogenesis is not the only mechanism by which antidepressants counteract the effects of stress in animals.

The most interesting aspect of this paper, to my mind, was an essentially unrelated new finding. Stress was found to reduce the volume of several areas of the rat's brain, including the hippocampus and also the medial prefrontal cortex (mPFC). Unlike the hippocampus, this is an area known to be involved in motivation and emotion. Importantly, the authors found that following stress, the mPFC did not shrink because neurones were dying or because fewer neurones were being born, but rather because the existing neurones were changing shape - stress caused atrophy of the dendritic spines which branch out from neurones. Dendrites are essential for communication between neurones.

As you can see in the drawings above, stress (the middle column) caused shrinking and stunting of the dendrites in pyrimidal neurones from three areas relative to the unstressed rats (left), while those rats recieving antidepressants as well as stress showed no such effect (right). The cytostatic MAM had no effect whatsoever on dendrites. Further work found that antidepressants increase expression of NCAM1, a protein which is involved in dendritic growth.

So what does this mean? Well, for one thing, it doesn't prove that antidepressants work by increasing dendritic branching. Cheekily, the authors come close to implying this in their choice of title for the paper, but the published evidence shows no direct evidence for this. To find out, you would have to show that blocking the effects of antidepressants on dendrites also blocks their beneficial effects. I suspect this is what the authors are now working hard to try to do, but they haven't done so yet.

It also doesn't mean that taking Prozac will change the shape of your brain cells. It might well do, but this was a study in rats given huge doses of antidepressants (by human standards), so we really don't know whether the findings apply to humans. On the other hand, if Prozac changes the shape of your cells, this study suggests that stressful situations do too - and Prozac, if anything, will put your cells back to "normal".

Finally, I don't want to suggest that the neurogenesis theory of depression is now "dead". In neuroscience, theories never live or die on the basis of single experiments (unlike in physics). But it does suggest that the much-blogged-about neurogenesis hypothesis is not the whole story. Depression isn't just a case of too little serotonin, and it isn't just a case of too little neurogenesis or too little BDNF either.


J M Bessa, D Ferreira, I Melo, F Marques, J J Cerqueira, J A Palha, O F X Almeida, N Sousa (2008). The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling Molecular Psychiatry DOI: 10.1038/mp.2008.119

BBC: Bullies have Bad Brains

It was only last week that fMRI explained human hatred. Now it's revealed why some kids are horrible to others. Behold -

• "Bullying tendency wired in brain"

• "Bullies' brains may be hardwired to have sadistic tendencies"

• "Bullies' brains may be wired differently"

At least according to the BBC. You may not be surprised to learn that I'm skeptical. The Neurocritic is too, and indeed he beat me to it on this one, having critiqued the paper in question, "Atypical Empathetic Responses in Adolescents with Aggressive Conduct Disorder: A functional MRI Investigation" (here), remarkably quickly.

So I wasn't going to post about this study, but then The Onion covered it and inspired me to write something. Or rather, I'm going to write about the BBC's story, which was impressively rubbish even by the standards of neuro-journalism.

Basically, all of the statements I quoted at the top of this post are nonsense. They're science fiction. For one thing, this study wasn't about "bullies", but teenage boys diagnosed with severe "Conduct Disorder" (CD) who had committed multiple serious crimes. That's just nitpicking though. The study found, using fMRI, that when you show these CD-diagnosed boys videos of people suffering pain, different parts of their brain activate, compared to a control group of nice, non-violent boys. On some interpretations these areas included the brain's "pleasure centers" although this is controversial (and according to one commentator, it may be all based on someone flunking Anatomy 101).

I've previously berated laymen and journalists (and all-too-many neuroscientists) for being mystified by coloured blobs on the brain. They see them as revealing profound truths about humanity, and in particular, they see them as pointing to "nature" over "nurture" explanations for behaviour. This is rarely explicitly stated, but the BBC did so with the line "Bullies' brains may be hardwired to have sadistic tendencies". Essentially, they are implying that there is something biologically wrong with the brains of bullies which leads to them taking pleasure in the pain of others.

Is this completely unfounded? After all, the study did find differences in the brains of the bullies vs. the normal kids. Surely that means they were "wired differently", maybe even "hardwired" differently? Well, yes, but only in an utterly trivial sense. Everything we do is the result of our brain activity - and every difference between two people is a result of differences in the "wiring" of their brains. The only reason that you're not sitting here like me, writing a cynical blog post about neuroscience, is that you have the good fortune to have a brain wired differently from mine. The only reason I wrote the word "cynical" in that last sentence rather than, er, "snarky", is that my brain was wired that way. And so on.

Brains get wired the way they do through the interacting influence of genes (which tell your neurons how to grow and how to connect up during brain development) and the environment (e.g. as you learn to do something, new connections between your neurons are formed, sometimes leading to massive reorganization of the brain - a fascinating topic in itself).

So, that one person's brain is "wired differently" to another person's is a completely mundane fact. In fact it's as dull as saying that no two people have the same fingerprints. It tells you nothing about how it got to be wired the way it did, and in particular it tells you nothing about whether it was "hardwired" to be that way, i.e. genetically determined. Just by reading this post, your brain has got rewired! So even if you accept that this fMRI study found that bullies take pleasure in watching people suffer (dubious as I mentioned above), this tells you nothing about why. Maybe they were brought up to be sadistic. Maybe they see other people suffering a lot, and have got used to it.

So when the BBC quote Dr Mike Eslea as saying

A better understanding of the biological basis of these things is good to have but the danger is it causes people to leap to biological solutions - drugs - rather than other behavioural solutions

They should perhaps heed his warning rather than "biologizing" bullying so keenly.

The interesting thing about this is that the BBC journalist was probably not stupid. He or she is just human. I think we feel intuitively that any biological difference between two groups of people implies a biological cause for that difference, because we intuitively have a dualistic concept of the relationship between the mind and the brain. Mind and brain are separate entities. We can just about accept that the brain (biological) can influence behaviour (psychological), although we find this idea outlandish and vaguely disturbing, because we think it undermines the idea of "free will". But we can't see how behaviour could influence the brain. Hence the headline "Bullying tendency wired in brain". It's common sense, but it's also nonsense.