Connectome Read Free

neuroscientists don’t agree with the idea that dead brains can be informative and useful, however. Studying living brains is the only true way of doing neuroscience, they say, because:
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You are the activity of your neurons.
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    Here “activity” refers to the electrical signaling of neurons. Measurements of these signals have provided ample evidence that the neural activity in your brain at any given moment encodes your thoughts, feelings, and perceptions in that instant.
    How does the idea that you are the activity of your neurons square with the notion that you are your connectome? Though the two claims might seem contradictory, they are in fact compatible, because they refer to two different notions of the 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.
    Historically, the conscious self is the one that has attracted the most attention. 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 to 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.
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    In the pages ahead, I will present my vision for a new field of science: connectomics. My primary goal is to imagine the neuroscience of the future and share my excitement about what we’ll discover. How can we find connectomes, understand what they mean, and develop new methods of changing them? But we cannot chart the best course forward until we understand where we came from, so I’ll start by explaining the past. What do we already know, and where are we stuck?
    The brain contains 100 billion neurons,a fact that has overwhelmed even the most fearless explorers. One solution, as I explain in Part I, is to forget about neurons and instead divide the brain into a small number of regions. Neurologists have learned much about the functions of these regions by interpreting the symptoms of brain damage. In developing this method, they were inspired by the nineteenth-century school of thought known as phrenology.
    Phrenologists explained mental differences as arising from variations in the
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of the brain and its regions. By imaging the brains of many human subjects, modern researchers have confirmed this idea, using it to explain differences in intelligence as well as mental disorders like autism and schizophrenia. They have found some of the strongest evidence we have for the idea that minds differ because brains differ. The evidence is statistical, however—revealed only by