In Connectome (2012), Sebastian Seung describes our audacious effort to map the brain — to understand what makes us unique, from our personalities to mental afflictions.

Inside every one of our skulls lies an organ so vast in its complexity [100 billion neurons] that it might as well be infinite. (x)

A connectome is the totality of connections between the neurons in a nervous system. (xiii)

You are more than your genes. You are your connectome. (xv)

Since the connectome defines the pathways along which neural activity can flow, we might regard it as the streambed of consciousness. (xix)

A neuron takes your breath away with its beautiful shape. (39)

[The] cell body is only a small part of the picture. From it extend long, narrow branches that fork over and over, much like a tree. (40)

Neurons are polyamorous. Each embraces thousands of others as their branches entangle like spaghetti. Neurons form a tightly interconnected network. (40)

Neuroscientists would like to know how a vast network of neurons can think, feel, remember, and perceive — in short, how the brain generates the remarkable phenomena of the mind. (40)

Once you know that the brain uses chemical signals, it’s no longer surprising that drugs can alter the mind. (44)

In addition to chemical signals between neurons, there are also electrical signals in the brain. These travel within neurons. (47)

Millions of miles of gossamer neurites (neural branches) are packed inside your skull. (47)

A synapse converts an electrical signal into a chemical signal and then back. (49)

Neural pathways are directional [since] synapses are one-way devices. (49)

Sensory neurons (e.g., retinal photoreceptors) kick off the journey along neural pathways from stimulus to response. (52)

The secretion of neurotransmitter causes a tiny electrical effect in the next neuron, far below the level required to cause a spike. (53)

Where two branches join, electrical currents can meet as they flow toward the cell body, and can combine like the water of merging streams. (54)

Although a single synapse is typically too weak to drive a neuron to spike, multiple converging synapses can do the job. (54)

If they are activated simultaneously, they can collectively “convince” a neuron to spike. (54)

A spike is “all or none.” (54)

The cell body sums the electrical currents, effectively tallying the votes. (54)

A neuron actually weights its “advisors” unequally. (55)

[An excitatory neuron votes “yes” or abstains; an inhibitory neuron votes “no” or abstains.] (57)

In many brain regions, including the cortex, most neurons are excitatory. (57)

You could think of the brain as being like our society, which abounds in conformists but also harbors some contrarians. (57)

Spikes have two functions. The generation of a spike near the cell body represents the making of a decision. The propagation of a spike along the axon communicates the result of the decision to other neurons. (58)

Neuroscience contends that the unity of the mind is but an illusion hiding the spikes and secretions of a staggering number of neurons, a concept of the self that could be summed up as “I am many.” (60)

It’s neurons all the way down. (66)

Neurons are wired into a network with a hierarchical organization. (66)

A neuron that detects a whole receives excitatory synapses from neurons that detect its parts. (66)

The function of a neuron is defined chiefly by its connections with other neurons. (68)

Perception is the association of an idea with a stimulus, while thought is the association of an idea with another idea. (69)

Activation of the “magnolia neuron” excites the other neurons [like] a forest fire jumping from tree to tree, or a flash flood surging through a web of desert ravines. (71)

[Recollection can be bidirectional or sequential (e.g., song, story).] (73)

The connections of a cell assembly or synaptic chain are stable over time, which is how a childhood memory can persist into adulthood. (73)

 If two neurons are repeatedly activated simultaneously, then the connections between them are strengthened in both directions. [neurons that fire together, wire together] (81)

If two neurons are repeatedly activated sequentially, the connection from the first to the second is strengthened. (82)

Persistent spiking is the trace of short-term memory, while persistent connections are the trace of long-term memory. (91)

It’s the organization of the brain that matters, not the number of synapses. (110)

Neurons near each other in the brain tend to have similar functions. (119)

Most connections in the brain are between nearby neurons. (119)

A region’s function depends greatly on its wiring with other regions. (120)

A cortical area indeed has the potential to learn any function. (120)

There is a map of the body in Brodmann areas 3 and 4. (126)

There is a map of the external world in the inferior colliculus. (126)

You might think that your hand grew fingers by adding cells. No — actually, cell death etched away at your embryonic hand to create spaces between your fingers. (130)

Smelling whets the appetite, and listening saves relationships, but seeing is believing. (137)

Seeing has always been central to our beliefs. (137)

It’s at those moments when new means exist — when new technologies have been invented — that we see revolutions in science. (140)

Context turns out to be essential for the accurate perception of boundaries. (164)

A merge error is like a child’s use of the same crayon to color two adjacent regions in a coloring book. (164)

A split error is like the use of two different crayons to color a single region. (164)

Minsky aimed to make machines smarter [artificial intelligence]; Englebart wanted machines that made people smarter [intelligence augmentation]. (167)

There are hundreds of neuron types in the cortex alone. Neuroscientists continue to argue over their classification. (176)

It’s not even clear how to properly define the concepts of “brain region” and “neuron type.” (176)

In Plato’s dialogue Phaedrus, Socrates recommends “division…according to the natural formation, where the joint is, not breaking any part as a bad carver might.” (176)

This metaphor vividly compares the intellectual challenge of taxonomy to the more visceral activity of cutting poultry into pieces. (176)

“Carving nature at its joints” means cutting in places where connections are weakest. (176)

But most brain regions are not so obvious. The boundaries between cortical areas don’t seem like “joints” in the cortical sheet. A great many wires extend across them, connecting neurons on either side. (177)

Damage to a region impairs the corresponding elementary function. Damage to a connection impairs complex functions requiring cooperation between regions. (181)

Language is less localized that previously thought. (182)

Most mental functions require the cooperation of multiple cortical areas. (184)

Perhaps the finger movements of a piano sonata played from memory are driven by sequential spiking of a synaptic chain. (189)

The connectome retains the memory of the song. Whenever the bird sings, the memory is recalled by converting it into sequential spiking [like water flowing through a riverbed]. (193)

Some philosophers believe that it’s fundamentally impossible to simulate consciousness on a computer. (262)

Personally, I think that a sufficiently accurate brain simulation would be conscious. (263)

Book Notes

The map is not the territory. Nevertheless, we persist in mapping the brain. We aim to understand, to control, to create. So we touch the elephant and map a whole that’s less than the sum of its parts.

Yet even a blind man can see — patterns in the brain mirror patterns in the world — the connectome is a tree (hierarchy), river (network), mycelium (web) in love with its own (beautiful) reflection.

I imagine the opposite is true — patterns in the world mirror patterns in the brain. Like gods, our brains make things in their image, in their likeness. Forms are constructions of the mind, hints as to the wiring of a brain. We create mind maps, electrical circuits, transit systems, and social networks. We tell a story, sing a song, draw a circle. To reify our neural structures and sequences is art. When we do it right, it tingles.

As I work on Natural Information Architecture, I’m sharing notes and quotes from my sources of inspiration and provocation. As always, your questions and suggestions are welcome.