March 19, 2020

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How the Brain's Wiring
Makes Us Who We Are

by Sebastian Seung.
Houghton Mifflin Harcourt,
2012 (i-xxii, 359 pages)



"It is time to return to reality. We have each got one life to live, and one brain to do it with. In the end, every important goal in life boils down to changing our brains. We are blessed with natural mechanisms for transformation, but we find their limitations frustrating." (page 274)

"Beyond appealing to our curiosity and sense of wonder, can neuroscience give us new insights and techniques for changing ourselves?... I have argued that... changing our brains is really about changing our connectomes... Is it indeed true that minds differ because connectomes differ?... The next step will be to [use] molecular interventions that promote the four R's: reweighting, reconnection, rewiring, and regeneration." (page 274)

"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." (106)

"If a growth cone were expanded 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 have found that the growth cone acts like a dog sniffing its way home." (106)

"The surfaces of neurons are coated with special guidance molecules (growth cones), which act like scents on the ground. The interstitial spaces between neurons contain drifting guidance molecules that act like scents in the air. Growth cones are equipped with molecular sensors [that] can 'smell' the guidance molecules to find their destination." (106)

"The production of guidance molecules and sensors for these molecules is under genetic control ... That is how genes guide the 'wiring' of the brain." (106)


note = "The brainstem is critical for both respiration and consciousness. Its neurons generate signals that control the breathing muscles. If they fall inactive, breathing stops, and the patient cannot live without a mechanical ventilator. It is the brainstwem's role in breathing that gives brainstem death its close tie to the traditional notion of respiratory/circulatory death." (246)

note = "Another role played by the brainstem, perhaps even more important, is that it arouses the rest of the brain to conscousness. Our level of arousal goes up and down all the time, most dramatically in the sleep-wake cycle. Several populations of brainstem neurons, collectively called the reticular activating system, send their axons widely over the brain. These neurons secrete special neurotransmitters known as neuromodulators, chemicals that 'wake up' the thalamus and cerebral cortex. Without them the patient cannot be conscious, even if the rest of the brain is intact." (246-237)


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