Blogs / The Loom

Several commenters checked out the 3-D video of the world’s oldest fossil brain I posted yesterday and were struck by just how tiny the 300-million-year-old fish’s brain was in comparison to its braincase. Their verdict: shrinkage. In the paleontological sense of the word, not the Seinfeldian one. After death, brains that do not simply disappear sometimes get smaller. In this particular fish, Sibyrhynchus denisoni the brain must have gotten a lot smaller. Check out this image, in which the braincase is in red, and the brain is in yellow. (The scale bar is 5 millimeters.)

To move along the discussion of shrinkage, I thought it might be helpful to post the following passage from the paper itself, which will not be published until later this week in the Proceedings of the National Academies of Science. (For some reason, the journal lifts its embargo on us journalists days before they put papers online. So the link to the paper won’t work just yet.)

Assuming that this object is a mineral replica of the brain and some cranial ner ves, it shows an  import ant size discrepancy relative to the endocranial cavity. The question of the size and proportions of the brain, relative to the endocranial cav it y been much debated by early vertebrate paleontologists, but anatomical studies of ext ant vertebrates show that the brain generally fills the endocranial cavity and that size discrepancy between the brain and endocranial cavity invoked for some t axa is in fact a consequence of inadequate preservation techniques (10, 20, 21). The size discrepancy observed in Sibyrhynchus could be explained by shrinking of the brain tissues that might have occurred just before phosphatization, hence the position of the cerebellum far anterior to the otic capsule (18). Yet the optic tract reaches its foramen in a normal position, as do the other putative cranial nerves, thereby suggesting that the shrinking of the brain was minor.

Two possibilities come to mind. One is that the scientists are wrong, and the brain of Sibyrhynchus managed to shrink without disturbing the connections from the cranial nerves to their corresponding openings in the skull. Or they’re right, and this fish had a very tiny brain lodged deep inside a big space. Why there would be such a mismatch between brain size and braincase size the scientists can’t yet say. (Update: I forgot to mention that in many sharks and other fishes, the brain stops growing after birth, while the skull keeps growing.)  Which is all the more reason, as Pierre Kerner points out in the comments, for paleontologists to start opening museum drawers and do some more scanning. Let’s see what pattern emerges.

Update, minutes later: Alan Pradel, the lead author of the paper just left a comment on all this in the previous post. Here’s part of it:

…some extant fishes possess a small brain compared to the endocranial cavity (e.g. coelacanths). In iniopts, the nerves perfectly reach their respective foramen without any deformation and the overall morphology of the endocranial cavity is different from the morphology of the brain. Consequently we supposed that the brain did not fill the endocranial cavity. Concerning the optic foramen which is very large, a lot of other thing passed through it (e.g. the efferent pseudobranchial artery) as in extant ratfishes.

Paleontologists don’t go looking for brains, and I’m not surprised. I once got to hold a fresh brain in my hands (it was at a medical school–nothing fishy, I promise), and I can vouch that they are marvelously delicate: a custard for thinking. When any vertebrate with a brain dies, be it human, turtle, or guppy, that fragile greasy clump of neurons is one of the first organs to vanish. Scientists must infer what ancient brains were like very often by examining the case that held it–that is, if they can find a relatively intact braincase.

In recent years, scientists have been able to get important clues about brains by scanning the brain cases. They can create virtual fossils in their computers that reveal a wealth of details. Alan Pradel of the Museum National d’Histoire Naturelle in Paris and his colleagues recently scanned a 300-million-year old fossil of an ancient relative of sharks called Sibyrhynchus denisoni. They recognized many details of the skull. But when they looked closer, they saw something they could not quite believe. They saw something that looked like a fossilized brain.

Even without a brain, Sibyrhynchus is very interesting. It belonged to a group known as iniopterygians, whose closest living relatives are ratfish. While there are few species of ratfishes today, 300 million years ago they enjoyed a much bigger diversity. Iniopterygians were small (6 inches long) and had big eyes and pectoral fins, along with a club on their tail.

Pradel and his colleagues were pleased enough to see the braincase of Sibyrhynchus, but they were stunned to see a chunk of rock deep inside that looked like a very small fish brain (and I do mean small–its length was 7 mm, or a quarter of an inch). Fossils sometimes form strange structures, but Pradel and his colleagues are pretty sure that they’re actually seeing a brain. It has the shape of a ratfish brain, including the various sections of a ratfish brain. And it even has nerves that extend to the right places to connect to the eyes and ears.

You may be struck by how small the brain (yellow) is compared to the braincase (red). If the scientists are right, it’s a cautionary tale for those who would estimate the size and shape of ancient fish brains from their braincases. But perhaps, in the future, researchers will find more actual brains, and will be able to chart the evolution of these delicate organs in greater detail.

Source: Skull and brain of a 300-million-year-old chimaeroid fish revealed by synchrotron holotomography.

Movie: Courtesy of Alan Pradel

Here are excerpts from the panel discussion on the brain I moderated at the Franklin Institute. The scurrilous rumor about me and toy soldiers pops up about 4 minutes into Sam Wang’s discussion of false memories.

There are two things I really like to learn about: parasites and the human mind. And so I was intrigued to learn about some studies that suggest that we defend ourselves from infections not only with an immune system made up of cells and antibodies, but one made up of unconscious behaviors. It’s the topic of my new column about the brain in Discover. Other people can make us sick, and so perhaps we deal with them differently depending on our risk of getting sick. Take this study, from Carlos Navarrete, a psychologist at Michigan State University. He and his colleagues designed an experiment to compare how pregnant women respond to strangers. During the first trimester, both mother and child are particularly vulnerable to infection.

Navarrete and his colleagues had 206 pregnant women read two essays that were written, they were told, by students. One of the essays was by a foreigner who criticized the United States, the other by an American who praised the country. The women then had to rate the essayists for their likability, intelligence, and other qualities. Women in the first trimester were more likely than those in the second or third trimester to give a high score to the American and a low score to the foreigner. The pregnant women’s vulnerability to infection, Navar­rete concludes, brought with it a heightened disapproval of foreigners.

You can read the whole thing here.

Eleven years ago, the philosophers Andy Clark and David Chalmers made a bizarre claim: our minds were not limited to our brains, but extended out of our heads to encompass many things beyond us, from notebooks to hammers to language. I have been vaguely aware of their “Extended Mind Hypothesis” for a while now, but it wasn’t until I got a copy of Clark’s latest book, Supersizing the Mind: Embodiment, Action, and Cognitive Extension, that I spent some time getting to know it better. And as counterintuitive as it may be at first, it makes a fair amount of sense when you take a look at the results of recent experiments on real minds.

The original paper was, in hindsight, marvelously forward-thinking. I’m sure at the time it seemed like little more than a thought experiment. But today, when so many of us spend our days melded to computers or cell phones, relying on the Internet to organize our lives and answer our questions, the Extended Mind takes on a fresh urgency

There are plenty of people lamenting that all these machines and networks are crippling our minds. There are certainly good ways and bad ways to interact with our machines, but I have a hard time takng most technology Cassandras seriously. They have a comforting notion of how the mind works, but it’s not very useful for making sense of experiments scientists have run to learn about how our brains change dynamically as we invent and use new tools.

In my Brain column this month, I explore the Extended Mind, and what it means for us today. Check it out.

[Image of Andy Clark: The Edge]

You go for a swim, and you don’t even notice the tiny worm that burrows into your skin. It slips into a vein and surges along through the blood for a while. Eventually it leaves your blood vessels and starts creeping up your spinal cord. Creep creep creep, it goes, until it reaches your head. It curls up on the surface of your brain, forming a hard cyst. But it is not alone–every time you’ve gone for swim, worms have slithered into you, and now there are thousands of cysts peppering your brain.

And they are all making drugs that are seeping into your neurons. These drugs are a bit like Prozac, except far more sophisticated. They target certain neurons in certain parts of the brain, altering your behavior surgically, without unwanted side effects.

You don’t know what’s happening to you. But in situations in which you’d expect to feel scared or stressed, you just want to race around. You whirl in circles, doing whatever is necessary to get the attention of the very thing that terrifies you. Thanks to your uncontrollable flailing, that terror  finds you, and you are destroyed.

This is how I imagine you’d feel if you were a fish infected by a parasitic worm called Euhaplorchis californiensis.

I first encountered these remarkable parasites about ten years ago, when I took a trip out to Santa Barbara. In the estuaries and salt marshes along the California coast, one of the most common fish is the California killifish, and many of them carry the parasites. The parasites get their start in horn snails, where they produce offspring that can swim around the water searching for killifish. In their next phase, they live as cysts on the brains of the killifish, but in order to reach the stage when they can reproduce, they must get inside the guts of shore birds.

Kevin Lafferty, who studies these parasites, showed me a tank full of infected killifish. Despite having thousands of cysts on their brains, they could swim as vigorously as uninfected killfish. They can also get as much food as healthy fish and reproduce normally. But the fish in the tank acted oddly. They swam up near the surface of the water, making tight turns that showed off their glinting sides. It’s tempting to say that the fish are trying to make themselves as conspicuous as possible, but for a fish, it doesn’t really matter how conspicuous it is to a human. So Lafferty had run an experiment to see whether the birds thought the infected fish were acting oddly. There is indeed a difference–the infected fish are 10 to 30 times more likely to get grabbed by a fish bird than a parasite-free one.

Many parasites have evolved such wickedly elegant strategies for manipulating the behavior of their hosts for their own benefit (which I describe at more length in my book Parasite Rex). But exactly how they do this parasitological voodoo is quite mysterious. A number of studies suggest that parasites release chemicals that can precisely alter the way in which the nervous systems of their hosts work. But it’s easy for parasites to hide a potent drug in the normal flow of neurochemistry in the brain. It’s also possible, at least in some cases, that parasites don’t do much of anything to manipulate their hosts. Just being infected can affect how animals behave–in some cases making them sluggish, in some cases stressing them out.

Jenny Shaw, a post-doctoral researcher at the University of California at Santa Barbara, has been working with Lafferty and other colleagues to figure out how Euhaplorchis manipulates the killifsh. They’re reporting some early results in a new paper in the Proceedings of the Royal Society. While they haven’t found the Parasite Panic Pill just yet, they do have some intriguing results. They took tiny pieces from different regions of the brains of infected and clean killifish. In each chunk of brain, they measured levels of neurotransmitters such as dopamine and serotonin. To compare the effects of parasites to ordinary stress, they also looked at the brains of stressed killifish (you stress a killifish by lowering the water in its tank).

Shaw and her colleagues found that the brain of an infected fish is not the brain of a stressed fish. When healthy fish get stressed, they produce serotonin in a region of the brain called the raphe nuclei. The parasites block that response. The parasites also lowered serotonin in the hippocampus, while boosting dopamine in the hypothalamus. The more parasites a fish had, the stronger these effects were.

Shaw and her colleagues point out that in normal fish, a surge of serotonin can cause fish to freeze, which is a good way to hide from motion-sensing predators. By lowering the serotonin from the raphe nuclei, parasites may prevent fish from hiding from wading birds. Dopamine, on the other hand, stimulates fish to swim more and behave aggressively. It’s possible that a parasite-boosted level of dopamine also helps turn fish into bird breakfast.

It may be years before someone finds the molecules these parasites release to cause these changes in serotonin and dopamine. But in the meantime, it’s pretty mind-blowing to think that there are literally millions of fish in the waters off of California being drugged by their parasite overlord. Scientists may have to wait a while before they can speak definitively about the medicine chests of the puppet masters, but science fiction novelists (I’m talking to you, Scott Sigler) are welcome to start their engines.

Shaw et al, Parasite manipulation of brain monoamines in California killifish (Fundulus parvipinnis) by the trematode Euhaplorchis californiensis, Proceedings of the Royal Society doi:10.1098/rspb.2008.1597

[Image from Jenny Shaw's web site]

Something strange recently happened to me in Tennessee. I wasn’t actually in Tennessee when it happened. The strangeness emanated from there–actually, from one spot in Tennessee–and eventually reached me here up in New England.

It started with a column I wrote in the October issue of Discover, about the evolution of the human face. Sometimes people write letters to the magazine about my pieces. My editors dropped a note to let me know that all at once they got 40 60 letters about my column. All from the outskirts of Memphis. All pretty much identical in style and substance. Some had been written on a computer, but some were written by hand–young hands, judging from their appearance.

Here’s a sample…

“I enjoyed reading your article and was interested in the research done on how the face and its muscles work to make expressions. I however believe that the brain and facial expressions are not a byproduct of years of evolution but instead a fingerprint of intelligent design. You claim in your article, that the muscles of the face are the result of the transition of life from land to water, but where is the fossil record for the jump? None have been found. There is no proof of the evolution of water to land creatures.”

And a second…

“I would like to show you what I think may have happened. First off, there is the law of entropy. This law states that everything is in a state of going deeper into chaos. The brain could not have formed going from a blob of amino acid to a highly complex organ that is capable of generating the power that is does. That is going into a state of unity and order. According to natural laws, this is impossible. Only a creator is capable of doing this.”

And a third

“If the face is an irreducibly complex machine, which it is, it cannot evolve because the original face would be missing parts, which would make the whole machine non-fuctioning. This rules out the possibility of evolution in human faces.”

I don’t know if all these letters came from a single class or club. In any case, the folks at Discover asked me if I’d write something in response. So–to my correspondents from Tennessee:

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If you’d like to learn about some of the latest discoveries about the brain and find out where neuroscience is headed, please join me at the Franklin Institute in Philadelphia on Wednesday. I’ll be moderating a panel discussion packed with prominent neuroscientists. Here are the details:

The Franklin Institute, Discover Magazine and the National Science Foundation present a fascinating neuroscience symposium.

“Unlocking the Secrets and Powers of the Brain.”
Date: November 19
Time: 7:00pm
Event location: Franklin Theater
Admission: Free with advanced registration, please call 215.448.1254

Moderated by award-winning journalist Carl Zimmer, the discussion features Dan Levitin (best-selling author of This is Your Brain On Music), Michael Gazzaniga (Director for the SAGE Center for the Study of Mind at UC Santa Barbara), Rebecca Saxe (Assistant Professor of Cognitive Neuroscience at MIT), Sam Wang (Welcome to Your Brain) and Ron Mangun (Interim Dean of Social Sciences, a Professor of Psychology and Neurology, and the Director of the Center for Mind and Brain at the UC Davis). A book signing will follow.

Just spoke today on New Hampshire Public Radio about my latest Discover column on the battle between the parents. Listen here.

As I wrote in my story in the New York Times today, much of your DNA is shut down by molecules collectively known as epigenetic marks. Roughly 100 sites are notable exceptions to this rule: your mother’s copy of these stretches of DNA are silenced, while your father’s are free to make proteins and RNA–or vice versa. This imbalance, known as imprinting, is utterly fascinating, and when the imprinting system goes awry–when dad’s genes start becoming active when they shouldn’t, or when mom’s genes go quiet when they should be active–the effects can be catastrophic. I first became familiar with gene imprinting while writing an article for the Times a couple years ago about a scientist at Harvard named David Haig, who has a theory for how it had evolved. He argues that gene imprinting is the result of an evolutionary tug of war between mothers and fathers, because mammalian parents have an evolutionary conflict of interest.

Now a couple scientists are extending this conflict theory to explain why so many imprinted genes are turning up in psychiatric disorders, ranging from autism to schizophrenia. They argue that the conflict between our parents plays out in our brains, too. This morning you can read about this provocative idea in my latest Discover column on the brain, or in this article by Benedict Carey in the Times.

These articles ought to come with a disclaimer: when we write about conflicts between parents, we are speaking metaphorically. We are actually referring to the rise and fall of different genes over millions of years, as natural selection acts on populations of thousands or millions of individuals. Just because you inherited imprinted genes from your mother or father doesn’t mean they sat down and drew up plans for using to maximize their own reproductive success (unless your father was Dr. Evil, I suppose…) Nevertheless, this new research does add an extra dimension to Philip Larkin’s ode to all miserable kids, which Larkin recites in this video (if you haven’t heard it before, just be warned that there’s some old-time Anglosaxon profanity along the way):

One of Darwin’s lesser known obsessions was with faces–how we make different faces, and what they say about us. Today, psychologists and neuroscientists are discovering the hidden conversation between brain and face, with a lot of tools Darwin never had–MRI scanners, subcutaneous eletrodes, and Botox.

Botox?

Indeed. In fact, some recent studies with Botox raise the weird possibility that our national love affair with that face-freezing drug may be subtly altering the emotions of millions of people.

For more, check out my new column on the brain in the November issue of Discover.

[Illustration from Darwin's The Expression of Emotions via Darwin Online]

In the latest issue of Scientific American, I have a feature on the biology of intelligence. (Read it online at sciam.com or carlzimmer.com) I’ve been fascinated by the subject for a long time, and I decided recently that the time was right to put together an article.

What’s the news? That there is no news.

Allow me to explain…

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