The nature vs. nurture debate pitted the hard and social sciences against each other for decades, if not centuries, stirred by a central concern with consciousness, what it means to be human, what makes a person, and, perhaps most interestingly to us egocentric beings, what constitutes character and personality. In Connectome: How the Brain’s Wiring Makes Us Who We Are, MIT Professor of Computational Neuroscience Sebastian Seung proposes a new model for understanding the totality of selfhood, one based the emerging science of connectomics — a kind of neuroscience of the future that seeks to map and understand the brain much like genomics has mapped the genome.

A “connectome” denotes the sum total of connections between the neurons in a nervous system and, like “genome,” implies completeness. It’s a complex fingerprint of identity, revealing the differences between brains and, inversely, the specificity of our own uniqueness. Seung proposes a simple theory: We are different because our connectomes differ from one another. With that lens, he argues, any kind of personality change — from educating yourself to developing better habits — is a matter of rewiring your connectome.

That capacity is precisely what makes the connectome intriguing and infinitely promising — unlike the genome, which is fixed from the moment of conception, the connetome changes throughout life. Seung explains:

Neuroscientists have already identified the basic kinds of change. Neurons adjust, or “reweight,” their connections by strengthening or weakening them. Neurons reconnect by creating and eliminating synapses, and they rewire by growing and retracting branches. Finally, entirely new neurons are created and existing ones eliminated through regeneration. We don’t know exactly how life events — your parents’ divorce, your fabulous year abroad — change your connectome. But there is good evidence that all four R’s — reweighting, reconnection, rewiring, and regeneration — are affected by your experiences. At the same time, the four R’s are also guided by genes. Minds are indeed influenced by genes, especially when the brain is ‘wiring’ itself up during infancy and childhood.* […] The connectome theory of mental differences is compatible with the genetic theory, but it is far richer and more complex because it includes the effects of living in the world. The connectome theory is also less deterministic. There is reason to believe that we shape our own connectomes by the actions we take, even by the things we think. Brain wiring may make us who we are, but we play an important role in wiring up our brains.”

Harnessing the power of those four R’s, Seung believes, is the most important goal of neuroscience — but, given your connectome is 100 billion times larger than your genome and has a million times more connections than your genome has letters, it’s a daunting task. Still, new technologies and new directions of scientific curiosity are bringing us closer to understanding this microcosm of meticulously structured chaos.

At the heart of Seung’s vision is a new way of thinking about human personality, a fascinating and controversial subject we’ve previously explored. He proposes an apt metaphor, underpinning which is a desire not only to find and understand our connectomes, but also to develop methods for changing and optimizing them:

In the nineteenth century, the American psychologist William James wrote eloquently of the stream of consciousness, the continuous flow of thoughts through the mind. But James failed to note that every stream has a bed. Without this groove in the earth, the water would not know in which direction of the flow. Since the connectome defines the pathways along which neural activity can flow, we might regard it as the streambed of consciousness. The metaphor is a powerful one. Over a long period of time, in the same way that the water of the stream slowly shapes the bed, neural activity changes the connectome. The two notions of the self — as both the fast-moving, ever-changing stream, and the more stable but slowly transforming streambed** — are thus inextricably linked. This book is about the self as the streambed, the self in the connectome — the self that has been neglected for too long.”

In elaborating on this dichotomy of the self, Seung echoes Daniel Kahneman’s notion of the experiencing self vs. the remembering self:

One self changes rapidly from moment to moment, becoming angry and then cheering up, thinking about the meaning of life and then the household chores, watching the leaves fall outside and then the football game on television. This self is the one intertwined with consciousness. Its protean nature derives from the rapidly changing patterns of neural activity in the brain. The other self is much more stable. It retains memories from childhood over an entire lifetime. Its nature — what we think of as personality — is largely constant, a fact that comforts family and friends. The properties of this self are expressed while you are conscious, but they continue to exist during unconscious states like sleep. This self, like the connectome, changes only slowly over time. This is the self invoked by the idea that you are your connectome.”

Sample Seung’s insights with his 2010 TEDGlobal talk:

Scientific American has an excellent Q&A with Seung about Connectome.

* For more on this fascinating early wiring, especially as it applies to our emotional lives, see the excellent A General Theory of Love.

** For a different metaphor articulating an analogous concept, see Jonathan Haidt’s The Happiness Hypothesis, where he describes the self as the interplay between the conscious “rider” and the unconscious “elephant” he struggles to command.