lso throws in a bit of neurochemistry, assuming no prior knowledge of biology, chemistry or psychology.
Except for the last two chapters, the book is not so much about connectomes as about how to use connectomes to frame neuroscience. We learn about the tools of the neuroscience trade—how they work and why they are important. From there we learn how patterns of neural connections give rise to our perceptions of the world, our reactions to perception and, ultimately, our uniqueness. Although obtaining connectomes for even the simpler brain of the mouse is beyond our technological abilities today, Mr. Seung lays out the technical hurdles and proposes some more attainable near-term goals. But he also makes a passionate case for a decade-long investment of time and energy, comparable to the Human Genome Project, to advance the cause.
Even in the current speculative realm, the connectome is a fascinating, occasionally frustrating, subject. One view is that each connectome or connectivity map will give rise to one and only one brain state and that different connectomes cannot give rise to the same state. Yet the widespread use of pharmaceutical agents such as Prozac and Ritalin suggests otherwise—that knowing the connectome is unlikely to tell us all we need to know about a person's thoughts, feelings, opinions and personality.
The levels of various chemicals in our brains can clearly be altered pharmaceutically. They are also influenced by diet, exercise, stress and normal biological cycles. Even if we know how the neurons are connected and the strength of their synapses, the amount of dopamine, for example, that is available in the brain at any given moment will influence firing patterns. This could cause the same neural network (a group of connected neurons) to give rise to different thoughts or different networks to give rise to similar thoughts.
Despite the fact that we have different brains and different neuronal configurations, when you and I smell a skunk it seems likely that we have equivalent mental states that lead to the same conclusions. Knowing the wiring is a crucial operation in understanding the nature of thought, but it seems not to be enough; we also need to know the precise chemical soup du jour in the brain. And one more additional, crucial step is understanding which types of experiences and environmental events can change the brain's wiring and in what ways.
The last two chapters of Connectome will be catnip for futurists, as Mr. Seung lays out two possible benefits of understanding connectomes: the repair of cryogenically frozen brains and subsequent restoration of consciousness and the uploading of consciousness into computer simulations. In the best (but unlikely) case, either could lead to cognitive immortality. Although the claims are far-fetched, they are beautifully explained and analyzed—as I might have expected from a writer who has produced the best lay book on brain science I've ever read.
—Mr. Levitin is a professor of psychology and neuroscience at McGill University in Montreal. His books include This Is Your Brain on Music.