Blogs / The Loom

From time to time, I’ve asked around for a good estimate of how many neurons are in the human brain. Ten billion–100 billion–something like that, is the typical answer I get. But there are actually a trillion other cells in the brain. They’re known as glia, which is Latin for glue–which gives you an idea of how little scientists have thought of them. But without glia, our brains would be useless. Scientists don’t yet really understand all the things that glia do for us, but it looks as if they do a lot–perhaps even processing information in their own mysterious way.

In my brain column in the September issue of Discover, I consider the long-neglected neurological elephant in the corner. Check it out.

[Image from Neurophysiology for the Audiologist]

Two of my stories came out this week–one on the near future, and one on the distant past.

1. Global warming is beginning to drive evolution of plants and animals. And soon it will be shifting to high gear. Read more at Yale Environment 360.

2. You, me, and the mushroom over there are all eukaryotes. So are slime molds and Giardia. We all share a number of features that set us apart from prokaryotes like E. coli. The split between eukaryotes and other living things is arguably the deepest in all life. In this week’s issue of Science, I have an essay that looks at how the basic eukaryote cell, complete with nucleus, mitochondria, and all its other bells and whistles came to be. Check it out (here or here). And you can also listen to me talk about the question on this week’s Science podcast here.

Nature offers suggestions for summer reading in the latest issue, and  Microcosm is on the list. Don’t worry–just because the book is about E. coli doesn’t mean they’ll have to close the beach:

What is life? Why do creatures cooperate? Why do living things die? Carl Zimmer, a leading writer on evolution, finds answers to these and other big questions in the most humble of places — the common gut microbe, Escherichia coli. In Zimmer’s hands, E. coli becomes a window on to the basic properties of life and the ways that complex living systems can arise and change.

Zimmer weaves a narrative through the main principles of evolution, genetics and ageing, with stories of the people who made major breakthroughs along the way. His simple way of explaining complex ideas and his fast storytelling pace make for delightful reading. Each chapter contains ‘wow’ moments about bacteria and the joys and travails of the scientists who study them. The result is a scientific detective story that left me with a new appreciation of the trillions of microbes that live on and inside my body.

The editors also asked me for a suggestion, and I offered up Newton and the Counterfeiter by Tom Levenson.  The rest of the list looks good too, although I will probably have to abstain. I am determined to finish War and Peace, a few pages at a time if necessary, in this lifetime. Or maybe the next.

My latest story for the New York Times has just gone online. It continues my string of stories in which I look at the familiar and find it deeply strange. The previous one was about fireflies. Tomorrow’s story is about the surface of the ocean. It turns out to be a deeply weird thing–a gelatinous biofilm inhabited by a peculiar menagerie of microbes that play a vital role in our own well-being.

Check it out.

In my June brain column for Discover, I wrote about the bizarre idea that there are single neurons in your head that can respond to individual people. The so-called “grandmother cell” started out 40 years ago as a thought experiment riffing on Philip Roth’s novel Portnoy’s Complaint. By the 1970s, most neuroscientists considered it more of a joke than a valid concept, but in the years since it hasn’t quite gone away.

In my column, I described the work of the work of Rodrigo Quian Quiroga of the University of Leicester:

For the past eight years, he and his colleagues have been studying epilepsy patients who have had electrodes implanted in a region of their brains called the medial temporal lobe, as part of a study to identify the source of their seizures. Quian Quiroga showed the subjects 100 pictures. The pictures included photos and drawings of celebrities as well as landmarks and various familiar objects. The patients had to press one button if a picture was of a human face and another if it was not.

In their first such study, Quian Quiroga and his team were able to observe the individual activity of 993 neurons. They found that 132 of them responded to at least one picture. And of those responding neurons, 51 fired in response to only a single person or thing. One neuron responded only to Halle Berry, for example.

Amazingly, the “Halle Berry” neuron responded to any picture of her, including one in which she was dressed as the masked Catwoman. Even the name Halle Berry triggered that neuron, which was silent at the sight of other actresses or their names.

Quian Quiroga does not, however, believe these neurons are grandmother cells, at least as they were initially conceived. He suspect that a very sparse network of neurons–perhaps hundreds out of the billions in our heads–can develop this kind of response to an individual. Quian Quiroga just happen to stick his electrodes near single neurons that belonged to these networks.

Which brings us to Quian Quiroga’s latest paper, published in Current Biology. He analyzed the signals from 750 electrodes implanted in seven patients as they looked at pictures of some celebrities like Oprah Winfrey. Quian Quiroga found neurons that responded strongly to the sight of these individuals–and they also responded strongly to their written names and even the sounds of their names.

Quiroga and his colleagues also ran the same test using themselves rather than the celebrities to probe for neurons. They discovered neurons that responded strongly only to individual researchers, too–and once more, the same neurons responded to the sight and sound of their name. Bear in mind–the patients had only met the scientists a day or two earlier. So these neurons had developed their grandmother-ish response in a very short time.

These results offer some clues to how these sparse networks are arranged. Some of the neurons probably get signals from other regions of the brain that recognize faces. Others tap into auditory networks, and others language centers. Yet, remarkably, the information from these far-flung parts of the brain get funneled into tiny sets of neurons that can then encode concepts of people.

They may not be the Grandmother Cells of legend, but in their own way, they’re very cool.

Reference:  Quian Quiroga et al., Explicit Encoding of Multimodal Percepts by Single Neurons in the Human
Brain, Current Biology (2009), doi:10.1016/j.cub.2009.06.060

Here is a song by Christine Lavin inspired by my recent firefly story. It is available for two days on her web site (and will resurface this fall on her next CD).

I think this is the second or third time a musician has riffed on something I’ve written. Listen, for example, to this darker tune based on the wasp that’s also a brain surgeon.

I will be on the public radio show The Takeaway at 720 am EST Tuesday to talk about fireflies. I’ll update this post with a link to the podcast when it’s online. [And here it is.]

Fireflies are the topic of my story on the cover of the New York Times science section tomorrow. It’s the result of a visit I paid last Friday evening to a meadow in Massachusetts, where I listened to Sara Lewis of Tufts University explain the sultry, complex tale of sex, deception, and death that was playing out in front of me.

I first got to know Lewis’s work last summer, when I decided I wanted to include fireflies in my next book, The Tangled Bank: An Introduction to Evolution. Lewis co-authored a fascinating review of firefly biology last year (free pdf from Lewis’s web site). I particularly liked this chart, which shows how different species have evolved different flash signals.

The male, flying around, releases a certain pattern of flashes–a single one second pulse followed by a five secondin the case of Photinus pyralis, for one example. And if a female P. pyralis, sitting on a blade of grass, likes what she sees, she responds three seconds later. Not one. Not six. Three. If she responds at the right interval, he knows he’s found a female of his own species and zeroes in, sending more flashes. She may also be signalling other males at the same time; which male she chooses may come down to subtle features of the flash pattern–for example, a rapid series of pulses as opposed to a slow one.

You can, as I discovered, speak their language with a penlight. You can even play the male or the female, depending on your mood.

There’s lots of strange business going on out among the fireflies. I didn’t have room in the article to describe some of Lewis’s new areas of research. Because female fireflies mate with several males, they can end up with sperm from several males inside them at once. Studies on other animals have suggested that females can choose which male’s sperm they’ll use to fertilize their eggs. Males can also inject chemicals with their sperm that increase their odds of fertilization. It’s clear that in many species, female preferences and male competition can continue after mating ends.

No one knows how this struggle plays out in fireflies. Adam South, one of Dr. Lewis’s graduate students, is investigating this side of the evolutionary equation. He is mating female fireflies with two males apiece and then collecting the eggs they lay. Using DNA tests, he’s determining the paternity of the eggs. Perhaps the males with more attractive flashes have more offspring.

What scientists like Lewis know about fireflies is remarkable, but it’s dwarfed by what they don’t know. Are fireflies on the decline, for example? Unfortunately, there’s no good long-term data. But that’s now an opportunity for some citizen-science you can get involved in. Lewis and some former students have helped organize Firefly Watch, based at the Boston Museum of Science. You can make your backyard part of biology’s new frontier.

As a science writer, I often find it sobering to read scientific history. Science works slowly, even though we wish it would work in nanosecond breakthroughs.

In 1913, for example, a Russian scientist named Nikolai Anichkov ran an experiment in which he had egg yolks fed to rabbits. On this cholesterol-heavy diet the rabbits developed atherosclerosis. The more cholesterol the rabbits ate, the bigger the deposits on their blood vessels became. It was a tremendous discovery, considered by some one of the greatest in medical history.

But it did not lead overnight to a treatment for heart disease. In fact, it did not even lead, on its own, to a clear understanding of how cholesterol ends up in the blood vessels. Instead, it focused the attention of later scientists on the question of cholesterol. It took many years for scientists to figure out the steps by which enzymes produce cholesterol molecules. Then scientists began searching for drugs that might interfere with those enzymes.

In 1971, six decades after Anichkov ran his egg-yolk experiments, Akira Endo of Tokyo Noko University and his colleagues, decided to see if microbes made natural cholesterol-fighting compounds (free pdf). They reasoned that such a compound would be a potent weapon against microbial competitors, since cholesterol and related molecules are essential for building cells. In 1973 they found a fungus that blocks a key enzyme in the cholesterol pathway. It took more than another decade before drugs based on Endo’s explorations, known as statins, reached the market. Today drugs like Lipitor are prescribed to millions of people.

If a journalist wrote an article on Anchikov’s intial research, the most accurate headline would have been something like: “RUSSIAN SCIENTIST DISCOVERS LINK BETWEEN MOLECULE AND HEART DISEASE. WILL LEAD TO POWERFUL NEW MEDICINE IN EIGHTY YEARS.”

Of course, it would be a rare journalist who would be able to see eighty years in the future like that. And headlines about events readers won’t be alive to see can seem awfully remote. Anchikov’s discovery did not change the lives of the people who could have read about it at the time. Their grandchildren, yes.

I’ve been thinking about Anchikov recently, after having read a letter to the New England Journal of Medicine. It’s by Joel Hirschhorn of Harvard, on the subject of genomes.

A decade ago a complete sequence of the human genome was still a dream, although a dream close to becoming real. In a typical article from 1999, a reporter wrote that “scientists hope to treat diseases in much the same way that software engineers fix faulty computer programs, by isolating flaws in the code.” Once we could read the entire human genome, the article promised, nothing would be the same: “By identifying the genetic roots of illnesses like cancer and heart disease, some experts say, the science of the genome, or genomics, may make it possible for a child born today to live to 150–or, some say, much longer.”

What a difference a decade makes. Scientists have been finding many genetic markers for common diseases like heart disease and diabetes, but they’re not pointing the way to obvious treatments. The falling cost of DNA is letting scientists sequence genomes left and right–not just people’s genomes, but the genomes of their cancer cells and their microbes. And for now, scientists are drowning in data rather than plucking out new cures.

Hirschhorn wants the growing number of skeptics to keep history in mind. In his NEJM letter he writes,

New biologic insights do not guarantee a rapid translation into clinical practice; the latter will require great effort by basic, translational, and clinical researchers. The difficulty in translation is not unique to genetic discoveries: nearly a century and three Nobel Prizes separate the determination of the chemical composition of cholesterol from the development of statins. Each discovery of a biologically relevant locus is a potential first step in a translational journey, and some journeys will be shorter than others. With a more complete collection of relevant genes and pathways, we can hope to shorten the interval between biologic knowledge and improved patient care. 

In the next issue of Newsweek, I consider the near-term and the long-term future of genomes. My essay is called “The Gene Puzzle.” Check it out.

[Animation: Wikipedia]

Over at the Origins blog on Science’s web site, I take a look at what means to have sex–especially if you happen to be bacteria. Check it out.

I wrote about the two sides of our brains in April for Discover. Now some of the scientists whose research I highlighted have an article of their own in Scientific American, focusing on the ancient evolutionary origins of specializations in each hemisphere. So if you still have interhemispheric cravings, check it out!

Mind wandering is the subject of my new column for Discover. Far from just useless mental static, mind-wandering actually creates a distinctive pattern of activity in our brains–a pattern that suggests that it may actually be playing a crucial role in our mental life. Check it out.