Connectome: How the Brain's Wiring Makes Us Who We Are None Edition

This is a very good book with a very strange name. "Connectome" means the entire collection of our brain's neuronal connections, the totality of how we are wired together. The subtitle "How the Brain's Wiring Makes Us Who We Are" is a fairly accurate representation of what the book is about. I believe this is the author Sebastian Seung's first book and he demonstrates quite a talent for explaining complex topics to a general popular audience.

What I particularly like about this book was the material was not at all the usual popular neuroscience stuff. This book covered new ground for me and I think will for most other readers. Seung spends a decent amount of time in the beginning explaining some basics about neurons and how the brain works, but it is when you get into the central ideas of the book that it gets really interesting.

One thing I really liked about the book was how the author explained the technologies and challenges required to actually create a connectome of even simple brains much less a human. According to Seung we don't have computers powerful enough or the tools to even analyze a cubic millimeter of a bird brain's connectome, much less a complete human brain a million times that size.

The whole book was compelling and informative and I can easily recommend it to others. One thing to keep in mind however, is that it is very futuristic in a sense. Seung's ideas are very plausible to me but still unproven and speculative. The technology to validate them is not going to be available for many years.

I loved this absorbing book about neuroscience that took me through the past, present and future of the human brain. Though I'm not a scientist, I easily understood the challenges, clearly laid down by Dr. Seung, of finding connectomes. His very eclectic approach made it that much more interesting, as he argued from "first principles," and questioned all of his beliefs.

Prior to reading "Connectome," I had never heard the term, originally coined by Olaf Sporns and his colleagues in a 2005 paper. "A connectome is the totality of connections between the neurons in a nervous system. ... It is all of the connections." (xiii) "You may have heard of the $30 million Human Connectome Project, which was announced in 2010 by the U.S. National Institutes of Health (NIH). Most people don't realize that this project is only about regional connectomes, and has nothing to do with neuronal connectomes." (181) While Dr. Seung concedes that "in the immediate future, a regional connectome seems like the most useful kind for psychologists and neurologists" he is forward thinking to a day that all 100 billion neurons in the human brain are named, given a characteristic location and shape and are diagrammed. "To find connectomes, we will have to create machines that produce clear images of neurons and synapses over a large field of view." (140)

This is an ambitious goal. "We still don't know how many types [of neurons] there are, though we know the number is large. The brain is more like a tropical rainforest, which contains hundreds of species, than a coniferous forest with perhaps a single species of pine tree. One expert has estimated that there are thousands of neuron types in the cortex alone." (176) The connectome of a small roundworm (C. elegans) took seven years to "map" even though it has only 300 neurons scattered throughout its body. (xi) Seung imagines the human connectome could be completed by the end of this century thanks to rapid advances in technology for imaging the brain and slicing brain tissue, and high-speed computers to crunch the data.

This is all very fascinating and futuristic, but aside from connectome, this book is full of interesting information about intelligence, the effect of drugs on the brain, how the brain repairs itself after injury or stroke, as well as history and philosophy. For instance:

"Other animal species, such as lizards, are able to regenerate large parts of their nervous systems after injury. And human children regenerate better than adults do. In the 1970s, when physicians realized that children's fingertips regenerate like lizards' tails, they stopped attempting to reattach severed fingertips through surgery; now, they simply let the fingertips grow back. Hidden powers of regeneration might lie dormant in adults, and the new field of regenerative medicine seeks to awaken them." (221)

And:
"Neurons continue to grow branches well after birth. This process is called the "wiring" of the brain, since axons and dendrites resemble wires. Axons have to grow the most, since they are much longer than dendrites. Imagine the tiny growing tip of an axon, known as a "growth cone" for its roughly conical shape. If a growth cone were blown up to human size, its travels would take it to the other side of a city. How is the growth cone able to navigate such long distances? Many neuroscientists study this phenomenon, and they've found that the growth cone acts like a dog sniffing its way home. The surfaces of neurons are coated with special guidance molecules that act like scents on the ground, and the interstitial spaces between neurons contain drifting guidance molecules that act like scents in the air. Growth cones are equipped with molecular sensors and can "smell" the guidance molecules to find their destination. The production of guidance molecules and sensors for these molecules is under genetic control. That's how genes guide the wiring of the brain." (106)

For some inexplicable reason, I found the following most interesting:
"The need for inhibition might be the chief reason why the brain relies so heavily on synapses that transmit chemical signals. There is actually another kind of synapse, one that directly transmits electrical signals without using neurotransmitter. Such electrical synapses work more quickly, since they eliminate time-consuming steps of converting signals from electrical to chemical and then back to electrical, but there are no inhibitory electrical synapses, only excitatory ones. Perhaps because of this and other limitations, electrical synapses are much less common than chemical ones." (56)

Any reader interested in preserving his or her brain in hopes of achieving immortality will want to read the chapter, "To Freeze or to Pickle?" Cryobiology is examined scientifically as well as from ethical and philosophical points of view.

"Worthwhile things that have never been done can only be done by means that have never yet existed," Sebastian Seung tells us in CONNECTOME. Mapping the 100+ billion neurons in the human brain is certainly one such project, and we are far from having the means to do so.

But already, with the mapping and study of the 300 neurons in the C.elegans roundworm and ongoing development in imaging technology (such as the automated ultramicrotome), we are making strides toward understanding the structure and function of diverse neurons, and how their interactive network operates.

Author Seung is a professor of neuroscience at MIT, and a leading researcher on neural networks and the still-theoretical connectome. The term connectome, first coined in 2005, refers to the totality of connections between neurons. The field of neuroscience involves learning how neurons are strengthened, weakened, weighted and eliminated and how they connect and reconnect, rewire, and regenerate.

The first half of his book begins with chapters about: 1) the structure and role of neurons; 2) connectomes and their interconnectivity; 3) how memories are impressed and stored; 4) and genes. The next sections cover the development of imaging technologies and the lifelong task of reading and interpreting the voluminous data acquired.

Unfortunately, at this point, Seung comes across less as a scientist and more as a science fiction writer as he resorts to speculation about cryonics (brain and body preservation), uploading brains into computers, and immortality. The book would be much more substantial if he omitted the last few chapters.

Seung, however, is a talented writer with the unique ability to impart scientific theory in understandable language. Obviously possessing a highly associative brain himself, he is skilled at explaining fundamentals of neuroscience through the frequent use of everyday analogies.

He compares the process of dendrites spiking to a weighted voting system influenced by favoritism. All votes must be in before dendrites know they can spike, he tells us, further explaining that some votes count more than others -some neurons and their synapses transport more important signals than others do, and therefore have greater impact.

"If the axons and dendrites in the gray matter are like local streets, the axons of the white matter are like superhighways of the brain," he writes.

In another chapter, he briefly takes us on a "fantastic voyage". "Perhaps you are a protein molecule sitting on a molecular motor car running on a molecular track. You are being transported on the long journey from your birthplace, the cell body, to your destination, the outer reaches of the axon... To find an entire connectome, though, you'd have to explore every passage in the brain's labyrinth."

I was especially pleased that he compared RAM and hard drive memory to short-term and long-term memory in the brain - a comparison I make in computer skills classes I teach.

But I wish that Seung introduced us to the brain as a whole before zeroing in on neurons, and that he provided a detailed, labeled map of the parts of the brain. He included a lot of rough illustrations and diagrams, but few quality photos.

I thought that his discussion of factors contributing to memory was incomplete - he didn't even mention the emotional intensity of a learning experience, multi-sensory involvement, and mindful attention and intention, all factors I found to be critical during graduate training in education and psychology, as well as my personal brain fitness "workouts".

My primary criticism of the book, however, is that Seung doesn't differentiate enough between proven facts, generally accepted theories, his own personal theories, and pure speculation.

Nevertheless, his often chatty and informal yet highly informative writing style is enjoyable. His numerous and sometimes humorous analogies help us envision neural activity, understand the intricacies of the connectome, and appreciate the immense accomplishments and challenges of neuroscience. I rate CONNECTOME 4 stars.