The Brainiacs have landed at KITP! Last week was the start of a new program on the anatomy, development and evolution of the brain, which means the halls of KITP are now filled not just with particle physicists and cosmologists, but also scientists engaged in various aspects of neuroscience research. Ergo, I call them Brainiacs. That's one of the great things about the KITP: it's so very interdisciplinary in its scope, one never knows what sort of scientist one is likely to encounter on any given day, or what topics will be featured in the various scheduled talks. Today, for example, I can learn about gene networks in animal development, or mass determinations in decay chains with missing energy -- or both, if I'm feeling especially curious. Good times!
Neuroscience isn't a subject I cover much, beyond the occasional physics-based imaging technique (functional magnetic resonance imaging, anyone?). So why not have an unofficial "Brainiac Week" here at the cocktail party? We'll start with a post about the foundations of modern neuroscience. Last week I heard a talk by Winfried Denk of the Max-Planck Institute in Heidelberg, Germany, which was technically about brain circuit reconstruction using sectioning electron microscopy. My magpie mind (ooh! shiny!) got sidetracked early on, however, by the fact that most of major breakthroughs in early neuroscience came about because of the development of two critical technologies: histological staining techniques, and photomicroscopy.
We have Camillo Golgi to thank for the first one. In the late 19th century, he discovered that treating brain tissue with a silver chromate solution caused a small number of neurons to become darkly stained, revealing their detailed structure. (I've also seen the technique described as using a weak solution of silver nitrate to stain individual nerve and cell structures, in a so-called "black reaction.") Golgi's method revolutionized the field, so he can be forgiven for misinterpreting the structural organization of the central nervous system. He thought that nervous tissue was made up an intricate web of interconnected cells (the rete nervosa diffusa, or diffuse neural network), much like the human circulatory system. As scientific hypotheses go, it seemed a perfectly respectable working model, and was accepted as such by the scientific community, until a rapscallion upstart named Santiago Ramon y Cajal proffered a competing view based on his own experiments using a modified version of Golgi's staining technique.
Even today, Cajal is lauded as one of the key founders of modern neuroscience; Denk declared him the "most accomplished anatomist in neuroscience history." He was perhaps destined to turn science on its ear, since he was a notorious trouble-making hothead in his youth in Aragon, Spain. He was kicked out from numerous schools for his "poor behavior and anti-authoritarian attitude," and even landed in jail at the tender age of 11 "for destroying a town gate with a homemade cannon." I'm sure it was just a science experiment gone awry, a worthy price to pay for fostering natural inquisitiveness and scientific inquiry. (Rocket pioneer Werner von Braun got into trouble with authorities as a young boy, too, when he strapped a homemade rocket to a toy wagon and sent it speeding through the town square.)
Cajal had a sensitive, less pugnacious side as well: he was an avid painter, and very much wanted to be an artist. His father, a professor of applied anatomy in the University of Saragossa, nixed that idea, however, in favor of a more practical bent. The young Cajal was apprenticed first to a barber, then to a cobbler, before embarking on medical studies, graduating fro the medical school of Zaragoza in 1873. But he never really abandoned art: his gift for draughtsmanship would end up serving him very well in his medical and scientific career. (At right is Cajal's drawing of the neural circuitry of the rodent hippocampus, published in his Histologie du System Nerveux de l'Homme et des Vertebrates in 1911. That opus provided the foundation of modern neuroanatomy.)
His early career unfolded fairly predictably, Fresh out of med school, Cajal served as a medical officer in the Spanish Army, stationed for a year in Cuba, where he handily contracted both malaria and tuberculosis. He bounced back, though, got married, produced seven offspring, and became a professor at Valencia in 1881. A few years earlier, he used "every peseta saved from the service in Cuba" to purchase a rickety old microscope, which he used to study the structure of muscle fibers, among other things. And thus began what would become a most illustrious scientific career.
In 1887, at the age of 35, Cajal made a fateful trip to Madrid to meet with Luis Simarro Lacabra, a psychiatrist with an interest in histological research, who had himself just returned from Paris bearing brain tissue specimens stained with Golgi's method (developed some 14 years earlier). Cajal was writing a book on histological techniques, and collecting illustrations to accompany the text. Even though he'd only been studying the nervous system for about a year, he realized that the ordinary methods for studying nervous tissue were woefully inadequate. So the specimens Lacabra showed him proved to be a revelation. In his autobiography, years later, Cajal described his reactions on seeing nerve cells "coloured brownish black even to their finest branchlets, standing out with unsurpassable clarity upon a transparent yellow background. All was sharp as a sketch with Chinese ink."
The experience changed the course of Cajal's research, as he worked vigorously to apply the Golgi stain to tissues of the retina, the cerebellum and spinal cord. "As new facts appeared in my preparations, ideas boiled up and jostled each other in my mind. A fever for publication devoured me." And publish he did; his works and articles numbered more than 100 by the time he died in Madrid in 1934, not just on the fine structure of the nervous system, but also on muscles, tissues and other more general areas of pathology. (He also has an asteroid named after him -- an honor he now shares, apparently, with bloggers Bad Astronomer Phil Plait, fire-breathing atheist PZ Myers, and SkepChick Rebecca Watson. And I'll bet Cajal totally would have had a blog had the technology been available to him.)
More importantly, he arrived at very different conclusions than Golgi about the structure of the central nervous system. Recall that Golgi advocated the view that nervous tissue was a continuous web of interconnected cells. Cajal advanced the notion that the nervous system is comprised of billions of separate neurons, communicating with each other via highly specialized junctions (called "synapses" for the first time in 1897). This became known as the "neuron doctrine," which concludes that the basic units of the nervous system are individual cellular elements. Cajal also advanced the "law of dynamic polarization," concluding that nerve cells are polarized, receiving information on their dendrites and conducting information to distant locations through axons -- now a fundamental principle of neural connections.
Back then, it was a controversial view, since it contradicted Golgi's own model, but Cajal defended it fiercely, and later studies with electron microscopy bore him out by revealing that each neuron was enclosed within a plasma membrane. The two men ended up sharing the 1906 Nobel Prize in Physiology or Medicine. It seems fair. After all, Golgi invented the staining technique used by Cajal to form his hypothesis, and used it to produce the first descriptions of the different types of neurons, and the structure of glial cells, as well as the branches given off by the axon. Also, there are those in the field who argue that if you take into account the later discovery of electrical synapses, Golgi was at least partially correct that the central nervous system is a vast interconnected network -- it's just not the cells themselves that are connected.
It made for an interesting pair of Nobel lectures, though: the two men contradicted each other in their talks, each espousing his own theory of the organization of the central nervous system. For all the intensity of their scientific disagreement, the two men nonetheless respected each other's work. Writing about his Nobel honor, Cajal observed: "The other half was very justly adjudicated to the illustrious professor of Pavia, Camillo Golgi, the originator of the method with which I accomplished my most striking discoveries."
In addition to staining techniques, imaging techniques proved equally important to the development of neuroscience -- particularly the micrograph, a photo taken through a microscope to produce a magnified image of the sample. It's sometimes called a photomicrograph, and Wikipedia credits a Canadian inventor named Reginald Aubrey Fessenden with its invention, although he's best known for his pioneering breakthroughs in radio broadcast technology (as well as holding a 1926 patent for an "infuser," apparently a device for making tea). It's easy enough, in concept, to build a rudimentary photomicrograph: just attach a camera to the microscope in place of the eyepiece, place a specimen under the microscope as usual, and take as many pictures as you like.
It's a standard tool in forensics to examine trace evidence, and in biology (and neuroscience) to take magnified photos of cells and proteins -- and, if you happen to be Roman Vishniac, of insect eyes. Vishniac was a pioneer in the field, known for his photographs of living creatures in full motion, and -- more weirdly -- for taking a series of revolutionary photographs from the inside of a firefly's eye (the image at left is his daughter, Maria, seen through a firefly's 4600 tiny ommatidia). He also took pictures of the circulating blood inside a hamster's cheek pouch, and invented a method of colorization in the 1960s and early 1970s that used polarized light to penetrate cell structure in greater detail in an image.
The issue of better penetration turns out to be a critical one in modern efforts to image the brain, at least from what I gleaned from Denk's talk last week. Whereas pioneers like Cajal laid the foundations for modern neuroscience by imaging thin slices of dead brain tissue cells, researchers like Denk are coming up with inventive new ways to image living tissue -- or rather, combining lots of different optically-based techniques to see the previously "un-seeable."
For example, modern neurobiologists are combining things like multi-photon microscopy (Denk pioneered two-photon microscopy, in fact, which allows imaging of living tissue to a depth of about 1 millimeter), various types of scanning electron microscopy, fiberscopes, voltage sensitive dyes, and adaptive optics, among other tools, to engage in a kind of reverse engineering of the brain in action. The latter proved especially important because brain tissue can be tough to penetrate optically: the light scatters, and the wavefront distorts. Applying adaptive optics unscrambles the wavefront, so to speak, producing a clearer image. It's used quite a bit in astronomy to remove the effects of atmospheric distortion, compensating for any distorted wavefronts via deformable mirrors (or, less commonly, by employing materials with varying refractive properties).
Just to give you an idea of how daunting a task it can be to map out neurons and neuronal assemblies, Denk cited a seminal 1984 paper that laid out the "map" for the humble nematode (C elegans), a simple creature with a complex neurosystem model featuring 502 neurons. It took the scientists 10 years to complete the analysis, and the paper is a whopping 340 pages. It would take even longer to map out the neurosystem of a fruitfly brain, or a mouse brain, never mind the human brain.
Sure, Denk et al are using cutting-edge tools not previously possible before the advent of the modern computing age (among other advances), but ultimately, they're still doing optical imaging. Maybe that's why Denk's home page describes his work as a kind of "return of the light microscope to the front lines of biological research." By making the most of the tools available to them, and coming up with new approaches and combinations, Denk and his ilk are very much the intellectual descendants of Golgi and Cajal.