From Photon to Neuron: Light, Imaging, Vision

The January issue of Physics Today, the magazine of the American Institute of Physics, contains my review of Philip Nelson‘s new book From Photon to Neuron. The published review is the result of several iterations with the Physics Today book review editor, which improved it. Below, is my first draft. I think that readers of Intermediate Physics for Medicine and Biology will enjoy Nelson’s books.

From Photon to Neuron: Light, Imaging, Vision
Philip Nelson
Princeton University Press, 2017

Philip Nelson’s book From Photon to Neuron: Light, Imaging, Vision (Princeton University Press, 2017) completes a trilogy begun by Biological Physics (Freeman, 2014) and Physical Models of Living Systems (Freeman, 2015). These works establish Nelson as the preeminent textbook author at the intersection of physics and biology. All three books aim at upper-level undergraduates who already have studied a year of physics and calculus, but the texts are rich enough for the graduate level too.

Is From Photon to Neuron aimed at physicists interested in biology, or biologists interested in physics? Physics students will gain the most from this book. The mathematics (for example, the Fresnel integral) is beyond what most premed students are comfortable with. Biology majors will be challenged, but they need a book like this to improve their quantitative skills. Students with a weak command of calculus and no desire to improve it may find Sonke Johnsen’s excellent The Optics of Life (Princeton University Press, 2011) more palatable. A third-year physics major should be able to handle the math, except for some advanced topics in Part III that seemed out of place in an undergraduate book.

The wave and particle properties of light are both crucial for biology. For instance, diffraction limits your visual acuity, but a rod cell in your retina responds to a single photon. Nelson adopts a light hypothesis like that Richard Feynman presented in QED: The Strange Theory of Light and Matter (Princeton University Press, 1985): photons are governed by a probability amplitude that obeys a stationary-phase principle. Physics students will appreciate this powerful point of view; I am not sure what biology students will make of it. This approach highlights the intimate relationship between quantum mechanics, probability, and vision. For me, it works. Its disadvantage is that you must add a lot of e^iφs to explain simple concepts like reflection and refraction.

Readers who are interested primarily about vision, with little concern for light or imaging, might prefer Robert Rodieck’s masterpiece The First Steps in Seeing (Sinauer, 1998). The books by Rodieck and Nelson share several characteristics: eloquent prose, outstanding artwork (including some beautiful drawings by David Goodsell in From Photon to Neuron), and a quantitative approach that most biology textbooks lack. Nelson’s book, however, is more useful for teaching; it includes homework problems, end-of-chapter summaries, and recommendations for additional reading. Many of the homework exercises require analyzing data that you can download from the author’s website (www.physics.upenn.edu/~pcn). To do these exercises, you must know how to program a computer using MATLAB or similar software (you can download Nelson’s free Student Guide to MATLAB from his website). One critical skill students gain when taking a class using From Neuron to Brain is the ability to write short computer programs to analyze data numerically. Nelson teaches using words, pictures, formulas, and code to construct models and interpret data. His books provide a masterclass in how to integrate these four different approaches into a complete learning experience. Most biology books combine words and pictures, and a few include equations. Nelson’s emphasis on code—or at least his insistence that the students write their own code—sets his books apart. Computerphobes may hesitate initially, but they will gain the most from numerical modeling.

From Photon to Neuron covers topics throughout biological physics. For instance, fluorescence microscopy is a theme Nelson introduces early and revisits often. He devotes one chapter to color vision and another to superresolution microscopy. My favorite chapter begins with Rosalind Franklin’s iconic x-ray diffraction pattern of DNA, and then develops just enough theory to explain how Watson and Crick could, at a glance, obtain the key information they needed to derive their famous structure. Nelson presents enough electrophysiology to describe how absorption of a photon by rhodopsin causes a voltage signal across the neural membrane, and enough physical optics to explain the iridescence of butterfly wings. The network diagrams of signaling cascades seemed a little dry, but that may reflect my own tastes rather than Nelson’s presentation. Other topics include photosynthesis, Fluorescence Resonance Energy Transfer (FRET), and two-photon imaging.

Overall, I found From Photon to Neuron to be an outstanding textbook; a worthy successor to Biological Physics and Physical Models of Living Systems. Philip Nelson has done it again. His books define the field of biological physics.

Brad Roth
Oakland University
Rochester, Michigan

Brad Roth is a professor of physics at Oakland University, and is coauthor with Russell Hobbie of Intermediate Physics for Medicine and Biology (Springer, 2015).