Science Daily has a story titled:
Small Hairy Balls Hide Foul-Tasting Healthful Enzymes
It has nothing to do with the brain or with neuroscience, but how could I ignore reading an article with that title? And now sharing it with you... Basically, it looks like a Dutch group has figured out a way to package enzymes so that you don't have to taste them, and so they don't break down or lose potency before they get to your stomach or small intestine (or, as flight attendants like to say, wherever their final destination may be). Could be a cool new tool for drug delivery, but then, you'd have to be okay with putting small hairy balls in your mouth.
Monday, November 30, 2009
Saturday, November 28, 2009
Facilitated Communication
It's like a Ouija board only much, much worse. Here's a link to give you some idea of what I'm talking about. Basically someone is claiming this guy is not brain dead because they can pick up his hand and use it to type words on a keyboard. I, like PZ Myers, would like to see how well he answers the questions being asked when the "facilitator" is blindfolded. Anyway, hopefully now the cartoon makes sense.
Wednesday, November 25, 2009
Tryptophan and Turkey (Again)
So, I likely won't get to post anything tomorrow what with traveling and then eating and drinking followed by more eating and drinking and then some more eating for good measure. Since I won't be posting anything, enjoy this lovely e-card from someecards.com, and the blog version of a rebroadcast in the form of a link to my post from a few days ago explaining how tryptophan in turkey is not the culprit for your thanksgiving day drowsiness. If anything is to blame, it's the booze and all the "carbage". Here's the link to the turkey/tryptophan post, in the meanwhile...
Brain size: is bigger better? or, Of mice and men (and elephants)
What would you say if I told you there may be a way to increase your brain size? Would you be interested?
If you are, you're probably not alone, but would having a bigger brain make you smarter? Or would you just be throwing your money away?
Sadly, most of the evidence suggests that overall brain size is not a critical determinant of intelligence or cognitive function, and in some cases, having a bigger brain can actually be a bad thing.
Now, I was planning on writing a nice long post about how bigger is not always better when it comes to the brain, particularly when we look at different animals, but, I just read this article on ScienceDaily (http://www.sciencedaily.com/releases/2009/11/091117124009.htm) that sums things up pretty well. I'll just give a quick example that I think is quite convincing:
the brain of an Asian elephant is obviously larger than that of your average human (about 7.5 kilograms, where the human brain is, on average, a little less than 1.5 kilograms). Though, I think we will all agree that humans are smarter than elephants (if only slightly). To get around this blatant difference between humans and elephants, some people have argued that proportional brain size is what matters. That is, if you take the size (or mass) of the brain and divide it into the size of the whole animal, you get a ratio that describes the size of the brain in proportion to the the rest of the body. This works well when you look at humans and elephants, where, in humans, the mass of the brain over that of the body gives a ratio of about 2.1%, and in Asian elephants, about 0.15%. And to some extent, this approach works for other comparisons, where there are several examples that make sense (the ratio is larger in "smarter" animals), HOWEVER... there are definitely many examples where this doesn't work, for instance, when you look at mice, the ratio of brain weight over bodyweight is 3.2%, about one and a half times more than the ratio in humans. So, if bigger is always better, then either mice or elephants are smarter than people... which, despite the popularity of Sarah Palin's new book, is still highly doubtful.
So, comparisons across different species suggest that bigger brains don't equal smarter animals (even when you take overall body size into account). But what about if you compare humans to other humans? Here, there is some evidence that bigger is better (that's what she said), though again there are many exceptions and reasons for questioning that evidence (he retorted defensively). For example, when we look at the fossil record, we see that, as humans evolved, our skull cavities got bigger, suggesting that our brains got bigger as we got smarter (though, again there are exceptions, like Neanderthals whose brains may have been bigger than our own). When we look at more recent evidence in humans, we see some interesting things. For example, boys have larger brains (on average) than girls (which remains the case in adulthood as well). But does that mean boys are smarter than girls? Well, if we look at average SAT scores, boys do tend to score higher than girls, BUT, if we look at grades (in co-ed institutions) girls get better grades than boys do. So where does that leave us? It leaves us with no clear evidence that one sex is any smarter than the other, despite the difference in brain size. (The funny thing is, when we look at brain size as a proportion of total body size, girls actually have bigger brains than boys do, of course that still doesn't help us).
If we try to ignore the confusion of comparing men and women (or boys and girls as the case may be), there are some reports (based on data from MRI scans) that suggest bigger brains do correlate with higher IQ scores (which are certainly a limited, and perhaps biased measure for intelligence, but still interesting, and not completely irrelevant). However, these are weak correlations, and they do NOT demonstrate a hard and fast rule (see the very end of this post for a more detailed explanation of what I mean). For example, though he wasn't included in the MRI studies, one famous exception to this idea is Albert Einstein. When pathologists examined Einstein's brain after his death they found that it was not any larger than your average human brain, though I'd be willing to bet he would score pretty high on an IQ test.
In addition to the fact that these correlations were weak, there are a couple other points that make this evidence questionable (as to what it really means, if anything)...
1. several variables can change brain size over short periods of time. For example, drinking alcohol temporarily shrinks the brain, which means if anyone in these studies was hungover, they would likely appear to have a smaller brain and also probably wouldn't do so well on the IQ test. Other factors that are known to affect brain size include diet, exercise, marijuana, medication, and even meditation. Given the relative ease with which these things can alter brain size, it seems more difficult to tie any measure to absolute brain size since brain size is obviously not absolute.
2. IQ tests may not indicate a person's overall intelligence. That is, someone with a smaller brain may not have done as well on an IQ test, but they may be much more skilled in some other form of intelligence, like art (painting, sculpture, or music, etc.). We all know that Mozart was a genius (whose music can actually make you perform better on IQ type tests) and yet, he would probably not score so high on an IQ test.
3. Correlation is not cause. I have talked about this before. Even if we assume the data is unequivocal (that is, an almost perfect correlation, where 100 percent of the time a bigger brain is associated with greater intelligence) we still can't say that having a bigger brain causes people to be "smarter". Perhaps, brains get bigger with use, and therefore, people who study more or who have more years of education (and can therefore score higher on an IQ test) have slightly larger brains. For example, a study conducted about a decade ago with London cab drivers suggested that, at least a part of the brain might be able to get bigger with use. The study showed that the hippocampus (which is important for remembering where things are located) was bigger in cab drivers than in regular commuters, and cabbies who had been on the job for many years had larger hippocampi than cabbies who had only been working for a shorter time. While this isn't definitive, and doesn't say anything about other parts of the brain, it does suggest that brain growth in response to use or practice is a reasonable hypothesis.
So, what's the answer? Are bigger brains better? I think, despite the correlations between brain size and IQ, we still have to say NO.
One final piece of evidence I would like to offer is the presence of a condition (in humans) called megalencephaly, which literally means "large brain". Megalencephaly is characterized by a brain that is unusually large or heavy when compared to average brain size, and while it is suspected that the causes are genetic, they are not fully known. Interestingly, megalencephaly often results in decreased intelligence and mental retardation, which seems pretty convincing evidence that simply having a bigger brain does not confer any improvements in cognitive abilities. Of course, another condition known as microencephaly, or "small brain", also results in mental retardation and, often, early lethality. Together, these extreme conditions suggest that our brains work best within a range of sizes that are reasonably close to average. So if you have an average sized brain, be grateful, and know that, you're in good company (with Einstein), and while there may be other factors determining how smart you are (environmental factors like education level, or diet and exercise, or genetic and biological factors, like how many receptors for neurotransmitters your nerve cells make), brain size is likely not one of them.
___________________________________________________________________________________
The statistical measure for a correlation is the r value. In the MRI studies the r values ranged from 0.35 to 0.51, which may be statistically significant, but suggest a fair amount of deviation (what we would call a "weak" correlation). "r" values range from -1 to +1, with -1 being a perfect negative correlation (one thing gets smaller while the other gets bigger), +1 being a perfect positive correlation (two values get bigger together), and 0 being no different from random chance (the two variables don't seem to be related to each other at all). While getting an r value of 0.4 or 0.5 is definitely meaningful (what we call "statistically significant"), it suggests that there are a fair number of people who break from the trend. "Significance" in terms of statistics, signifies that the relationship being studied (in this case between brain size and IQ score) is not random, or likely doesn't reflect measures you would get by chance. To give you a simple example of what it means to be non-random, or not by chance, think of the simple comparison between two individuals where chance for a given variable is 50 percent (like flipping a coin, 50 percent chance of heads, 50 percent chance of tails). If you come across two people with different brain sizes, the MRI data suggests it is likely that more than fifty percent of the time, the person with the bigger brain will score better on an IQ test than the person with the smaller brain. However, a greater than 50 percent chance is NOT a hundred percent certainty. So, some of the time (less than 50 percent, but still greater than 0 percent), the person with the smaller brain will be "smarter" than the person with the larger brain (at least when measured by IQ).
If you are, you're probably not alone, but would having a bigger brain make you smarter? Or would you just be throwing your money away?
Sadly, most of the evidence suggests that overall brain size is not a critical determinant of intelligence or cognitive function, and in some cases, having a bigger brain can actually be a bad thing.
Now, I was planning on writing a nice long post about how bigger is not always better when it comes to the brain, particularly when we look at different animals, but, I just read this article on ScienceDaily (http://www.sciencedaily.com/releases/2009/11/091117124009.htm) that sums things up pretty well. I'll just give a quick example that I think is quite convincing:
the brain of an Asian elephant is obviously larger than that of your average human (about 7.5 kilograms, where the human brain is, on average, a little less than 1.5 kilograms). Though, I think we will all agree that humans are smarter than elephants (if only slightly). To get around this blatant difference between humans and elephants, some people have argued that proportional brain size is what matters. That is, if you take the size (or mass) of the brain and divide it into the size of the whole animal, you get a ratio that describes the size of the brain in proportion to the the rest of the body. This works well when you look at humans and elephants, where, in humans, the mass of the brain over that of the body gives a ratio of about 2.1%, and in Asian elephants, about 0.15%. And to some extent, this approach works for other comparisons, where there are several examples that make sense (the ratio is larger in "smarter" animals), HOWEVER... there are definitely many examples where this doesn't work, for instance, when you look at mice, the ratio of brain weight over bodyweight is 3.2%, about one and a half times more than the ratio in humans. So, if bigger is always better, then either mice or elephants are smarter than people... which, despite the popularity of Sarah Palin's new book, is still highly doubtful.
So, comparisons across different species suggest that bigger brains don't equal smarter animals (even when you take overall body size into account). But what about if you compare humans to other humans? Here, there is some evidence that bigger is better (that's what she said), though again there are many exceptions and reasons for questioning that evidence (he retorted defensively). For example, when we look at the fossil record, we see that, as humans evolved, our skull cavities got bigger, suggesting that our brains got bigger as we got smarter (though, again there are exceptions, like Neanderthals whose brains may have been bigger than our own). When we look at more recent evidence in humans, we see some interesting things. For example, boys have larger brains (on average) than girls (which remains the case in adulthood as well). But does that mean boys are smarter than girls? Well, if we look at average SAT scores, boys do tend to score higher than girls, BUT, if we look at grades (in co-ed institutions) girls get better grades than boys do. So where does that leave us? It leaves us with no clear evidence that one sex is any smarter than the other, despite the difference in brain size. (The funny thing is, when we look at brain size as a proportion of total body size, girls actually have bigger brains than boys do, of course that still doesn't help us).
If we try to ignore the confusion of comparing men and women (or boys and girls as the case may be), there are some reports (based on data from MRI scans) that suggest bigger brains do correlate with higher IQ scores (which are certainly a limited, and perhaps biased measure for intelligence, but still interesting, and not completely irrelevant). However, these are weak correlations, and they do NOT demonstrate a hard and fast rule (see the very end of this post for a more detailed explanation of what I mean). For example, though he wasn't included in the MRI studies, one famous exception to this idea is Albert Einstein. When pathologists examined Einstein's brain after his death they found that it was not any larger than your average human brain, though I'd be willing to bet he would score pretty high on an IQ test.
In addition to the fact that these correlations were weak, there are a couple other points that make this evidence questionable (as to what it really means, if anything)...
1. several variables can change brain size over short periods of time. For example, drinking alcohol temporarily shrinks the brain, which means if anyone in these studies was hungover, they would likely appear to have a smaller brain and also probably wouldn't do so well on the IQ test. Other factors that are known to affect brain size include diet, exercise, marijuana, medication, and even meditation. Given the relative ease with which these things can alter brain size, it seems more difficult to tie any measure to absolute brain size since brain size is obviously not absolute.
2. IQ tests may not indicate a person's overall intelligence. That is, someone with a smaller brain may not have done as well on an IQ test, but they may be much more skilled in some other form of intelligence, like art (painting, sculpture, or music, etc.). We all know that Mozart was a genius (whose music can actually make you perform better on IQ type tests) and yet, he would probably not score so high on an IQ test.
3. Correlation is not cause. I have talked about this before. Even if we assume the data is unequivocal (that is, an almost perfect correlation, where 100 percent of the time a bigger brain is associated with greater intelligence) we still can't say that having a bigger brain causes people to be "smarter". Perhaps, brains get bigger with use, and therefore, people who study more or who have more years of education (and can therefore score higher on an IQ test) have slightly larger brains. For example, a study conducted about a decade ago with London cab drivers suggested that, at least a part of the brain might be able to get bigger with use. The study showed that the hippocampus (which is important for remembering where things are located) was bigger in cab drivers than in regular commuters, and cabbies who had been on the job for many years had larger hippocampi than cabbies who had only been working for a shorter time. While this isn't definitive, and doesn't say anything about other parts of the brain, it does suggest that brain growth in response to use or practice is a reasonable hypothesis.
So, what's the answer? Are bigger brains better? I think, despite the correlations between brain size and IQ, we still have to say NO.
One final piece of evidence I would like to offer is the presence of a condition (in humans) called megalencephaly, which literally means "large brain". Megalencephaly is characterized by a brain that is unusually large or heavy when compared to average brain size, and while it is suspected that the causes are genetic, they are not fully known. Interestingly, megalencephaly often results in decreased intelligence and mental retardation, which seems pretty convincing evidence that simply having a bigger brain does not confer any improvements in cognitive abilities. Of course, another condition known as microencephaly, or "small brain", also results in mental retardation and, often, early lethality. Together, these extreme conditions suggest that our brains work best within a range of sizes that are reasonably close to average. So if you have an average sized brain, be grateful, and know that, you're in good company (with Einstein), and while there may be other factors determining how smart you are (environmental factors like education level, or diet and exercise, or genetic and biological factors, like how many receptors for neurotransmitters your nerve cells make), brain size is likely not one of them.
___________________________________________________________________________________
The statistical measure for a correlation is the r value. In the MRI studies the r values ranged from 0.35 to 0.51, which may be statistically significant, but suggest a fair amount of deviation (what we would call a "weak" correlation). "r" values range from -1 to +1, with -1 being a perfect negative correlation (one thing gets smaller while the other gets bigger), +1 being a perfect positive correlation (two values get bigger together), and 0 being no different from random chance (the two variables don't seem to be related to each other at all). While getting an r value of 0.4 or 0.5 is definitely meaningful (what we call "statistically significant"), it suggests that there are a fair number of people who break from the trend. "Significance" in terms of statistics, signifies that the relationship being studied (in this case between brain size and IQ score) is not random, or likely doesn't reflect measures you would get by chance. To give you a simple example of what it means to be non-random, or not by chance, think of the simple comparison between two individuals where chance for a given variable is 50 percent (like flipping a coin, 50 percent chance of heads, 50 percent chance of tails). If you come across two people with different brain sizes, the MRI data suggests it is likely that more than fifty percent of the time, the person with the bigger brain will score better on an IQ test than the person with the smaller brain. However, a greater than 50 percent chance is NOT a hundred percent certainty. So, some of the time (less than 50 percent, but still greater than 0 percent), the person with the smaller brain will be "smarter" than the person with the larger brain (at least when measured by IQ).
Sunday, November 22, 2009
Mad cows and cannibals...
A new article in the New England Journal of Medicine (1) shows the recent evolution of a mutation in a population of people in Papua, New Guinea that is protective against the degenerative brain disorder known as kuru. Kuru is a prion disease which is a disease (specifically a transmissable spongiform encephalopathy) that is caused by proteins that act like viruses. That is, the proteins are transmissable (i.e. contageous) and though they don't replicate themselves like viruses or bacteria would, they somehow seem to be able to cause all the other similar proteins in their host/victim to misfold in a way that then causes the build up of neurodegenerative plaques which are often fatal. Mostly, these diseases are transmitted through the eating of meat, as in Mad cow disease (which is known as Bovine spongiform encephalopathy, or BSE, in animals, the mutated form of which, in humans, is called Creutzfeld-Jakob Disease, or CJD). Kuru is a lot like CJD or BSE, and was passed on in the tribes of Papua New Guinea by the practice of the eating of dead relatives in memorial services. Though this practice was ended in the 1950s, the populations of people in this area experienced kuru epidemics that shaped the evolution of their tribes. One tribe in particular seems to have a high prevalence of a mutation (G127V) that protects them against kuru. Since kuru is fatal (killing many women and children in these populations), it makes sense that this mutation would be selected for, and its prevalence would increase in the population. This is particularly exciting because, not only is this a great example of evolution in action (in humans no less!), but as of yet, there are no treatments for CJD or kuru, and these diseases are often, almost always, fatal. The discovery of this mutation in a population that has evolved a resistance to a prion disease will offer insights into how we might go about protecting the brains of those who haven't evolved a resistance to prion diseases, and hopefully save some lives.
1. Mead, Simon, Whitfield, Jerome, Poulter, Mark, Shah, Paresh, Uphill, James, Campbell, Tracy, Al-Dujaily, Huda, Hummerich, Holger, Beck, Jon, Mein, Charles A., Verzilli, Claudio, Whittaker, John, Alpers, Michael P., Collinge, John. A Novel Protective Prion Protein Variant that Colocalizes with Kuru Exposure. New England Journal of Medicine, 2009; 361 (21): 2056 DOI: 10.1056/NEJMoa0809716
1. Mead, Simon, Whitfield, Jerome, Poulter, Mark, Shah, Paresh, Uphill, James, Campbell, Tracy, Al-Dujaily, Huda, Hummerich, Holger, Beck, Jon, Mein, Charles A., Verzilli, Claudio, Whittaker, John, Alpers, Michael P., Collinge, John. A Novel Protective Prion Protein Variant that Colocalizes with Kuru Exposure. New England Journal of Medicine, 2009; 361 (21): 2056 DOI: 10.1056/NEJMoa0809716
Monday, November 16, 2009
You may feel sleepy on Thanksgiving... but it's not the turkey.
Since Turkey-day is around the corner, I thought I would bring up the very popular myth that tryptophan in turkey is what makes us all feel groggy on Thanksgiving. In an earlier post, I talked about how the amino acid tryptophan gets converted into serotonin, and then melatonin. Melatonin, as you may or may not know is the "sleep hormone". It is secreted by the pineal gland to help regulate our sleep/wake cycles which follow a circadian rhythm of about 24-25 hours. During the day, when it is bright and sunny we feel awake, then, as the day turns into night, we start producing more melatonin, and we get sleepy. Considering this, it's not too hard to see why tryptophan became the scapegoat for our Thanksgiving day sleepiness, but the truth is tryptophan, or really turkey in general has gotten a bad rap. First, tryptophan is a fairly prevalent amino acid, and there is actually plenty of it in most of the protein containing foods that we eat. Furthermore, turkey does NOT contain a higher level of tryptophan than most other common meats, fish, and poultry. For example, per 200 calorie serving, duck, pork, chicken, soy, sunflower seeds, several types of fish, and turkey all have about 440 - 450 mg of tryptophan, with turkey being the lowest in the group. Of course, that being said, even if turkey did have significantly more tryptophan than other meats, it is still questionable as to whether normally consumed levels of tryptophan can make you sleepy. While at first glance, the research seems to back the idea that tryptophan has sedative effects, these studies have used very large quantities to test for effects. For example, one study from 1975 suggested that consuming 5 grams of tryptophan (so, about 11 servings of turkey) did increase self-reported drowsiness, and a study conducted in 1989 found that a dose of 1.2 grams of tryptophan did not increase measures for drowsiness, but a dose of 2.4 grams did. These studies suggest that you would have to eat a lot of turkey (like, over a pound and a half) to get an effective dose. So, while it is possible that you may eat that much turkey on our most hallowed of gluttonous holidays, it is more likely that thanksgiving day drowsiness is the result of a coming together of many factors, a perfect storm if you will, of:
1. lots of food (which diverts bloodflow to the digestive tract),
2. much of the food is carbohydrate heavy stuffing and sweet foods like cranberry sauce, sweet potatoes, and desserts (which can cause an overproduction of insulin resulting in low blood sugar, and thus sleepiness, later on),
3. and then of course there are usually a couple of alcoholic beverages involved (with obvious sleep inducing effects).
Add all of that up with being in a nice, warm home, on a comfy couch, with football or parades or a fire flickering in the background, and what you have is a recipe for a nap. I'm kinda sleepy just thinking about it.
Have a Happy Thanksgiving!
1. lots of food (which diverts bloodflow to the digestive tract),
2. much of the food is carbohydrate heavy stuffing and sweet foods like cranberry sauce, sweet potatoes, and desserts (which can cause an overproduction of insulin resulting in low blood sugar, and thus sleepiness, later on),
3. and then of course there are usually a couple of alcoholic beverages involved (with obvious sleep inducing effects).
Add all of that up with being in a nice, warm home, on a comfy couch, with football or parades or a fire flickering in the background, and what you have is a recipe for a nap. I'm kinda sleepy just thinking about it.
Have a Happy Thanksgiving!
Wednesday, November 11, 2009
I'm a "No" man... oh, and alcohol doesn't kill brain cells.
So, I've been reading Randy Olson's new book Don't be such a scientist: talking substance in an age of style, and in it, he talks about the disconnect between the general public (in our modern overly stimulated society) and scientists (who cloister themselves in their labs and ivory towers). A large part of the communication breakdown he posits comes from the nature of science itself which is a bare bones, take no prisoners, purely data and fact driven culture that breeds overt skepticism at all costs. This is important for how science works and for maintaining integrity in research, and it can actually be quite helpful in making your experiments better, but when you are trying to convey your findings to a broader audience they tend to find all the negativity and information overload to be, well, boring. Partly this is because the attention of the average person is now a hot commodity, and the marketplace for the average joe's attention is filled with advertisers, marketers, politicians, television, music, movies, you tube, and on, and on. Spend a few minutes going on about the role of bone morphogenetic proteins, wnt-beta catenin signaling, hedgehog singnaling, and several other factors in the differentiation of stem cells in the development of different aspects of the central and peripheral nervous system, and zzzzzzz..... Of course, I don't know if its the training, or if people of a certain mind set just gravitate to science, but a lot of us are like that. We go off on our research as if its the most important thing in the world, and we are obsessed with facts and with being accurate, and, we are very negative, we are always questioning the validity of what we're seeing or being told (it's what we do, we get paid to be skeptical). And so, as I've been reading this book, I've realized that I am no different, and that even this whole blog is devoted to negativity. I have set out to debunk, demystify, and disprove many common misperceptions about neuroscience. I am a "no" man. That's not how this works... That idea is wrong... I have become the person who constantly annoys everyone by correcting their grammar, escept I do it with neuroscience. Well, I can't help it. It's who I am, and part of my nature as a scientiist. BUT... despite my obsession with factual accuracy and my desire to negate the myths that are out there, it doesn't mean I always have to be the bearer of bad news. For example, today, the myth I want to debunk is the myth that drinking (alcohol) kills brain cells. As it turns out, there is very little (if any) conclusive evidence to suggest that drinking alcohol kills brain cells. So where did this myth come from? Well the obvious memory loss and headaches that come from binge drinking suggested that some sort of brain damage was occuring. And more recently, MRIs have shown that the brain shrinks after drinking. Don't worry, it's only temporary, but apparently it shrivels like a prune. Also, alcohol can damage parts of cells known as neurites that form synapses which are the connections between cells that allow them to communicate. Synapses are critical for forming new memories, and it appears to be this aspect of alcohol's effects that result in the short term memory loss we've all experienced at some point or another. Of course all that being said, overdosing on alcohol (or alcohol poisoning) can most definitely cause cells to die (and could cause you to die). Also, drinking and driving could kill brain cells by smashing them into the windshield at 60 miles per hour. But if your just going to have a few drinks with some friends, live it up, and relax, confident in the knowledge that your brain cells aren't lightweights, but they're actually tough enough to handle a couple beers, and maybe even a shot or two. Hey, some studies have even suggested that moderate drinking can improve mental abilities. So maybe a glass or two of wine a night is the way to go (since it's good for your heart too).
Normally I link to a bunch of stuff to back up what I'm saying, but I am off to Wisconsin, so these links will have to suffice....
http://www.wonderquest.com/BrainCells.htm
http://www2.potsdam.edu/hansondj/HealthIssues/1103162109.html
Normally I link to a bunch of stuff to back up what I'm saying, but I am off to Wisconsin, so these links will have to suffice....
http://www.wonderquest.com/BrainCells.htm
http://www2.potsdam.edu/hansondj/HealthIssues/1103162109.html
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