Human Circuit Board

by Eric Hand

CONNECTOME:
How the Brain’s Wiring Makes Us Who We Are.
By Sebastian Seung.
Houghton Mifflin Harcourt. 359 pp. $27

Who are you? Once, that question was answered by philosophers. Today, it’s often the province of geneticists who parse our DNA for clues to our identity. In Connectome, Sebastian Seung, a neuroscientist at MIT, proposes a different source. The essence of personhood, he says, lies not so much in our genetic code as in the way the 100 billion neurons in each of our brains are wired to one another.

“Genes alone cannot explain how your brain got to be the way it is,” Seung writes. “As you lay nestled in your mother’s womb, you already possessed your genome but not yet the memory of your first kiss.” Forging memories, imagining the future, acquiring a skill—these acts all require changes in the brain that cannot have been preordained by your DNA. Key to Seung’s view is the way that structures in your brain—and the behavior of your person—evolve over your lifetime, in contrast to your genome, whose content is fixed. Neurons are plastic, constantly creating and destroying connections with one another. Moreover, the electrical sparks that course through them can spike with varying degrees of strength.

---

If you want ...