Mark Humphries - The Spike

Midafternoon is the devils time. The ebbing of your circadian rhythms collides with the digestion of an ill-considered lunch of hot dog and hummus to dull your mind and bring thoughts of a cheeky nap. But theres an all-hands meeting in the conference room in ten minutes, at which youve discovered that snoring loudly enough to drown out the CEOs always be coding speech is a no-no. Eat something, says inner you. On the desk abutting yours is the box for some homemade ginger, pear, and chocolate cookies that Dietrich brought for the 10:00 a.m. conference call with the South Africa officestrangely delicious, definitely tempting, disappointingly gone.

No, wait. Your eyes glimpse a rounded, crumbly edge. Theres one left. Your brain sparks to life, as you glance around to clock your coworkers locations and thinkcould I take that? After a moments hesitation, weighing the ethical dilemmas and more importantly confirming that no one has line of sight, you extend a hand.

In those few moments your brain is abuzz with electricity. Vital, surreptitious-cookie-obtaining electricity. Why?

FIGURE 1.1. Basic anatomy of the human brain. Most of the outside of your brain is the cortex.

Your brain uses electricity to communicate. Each nerve cell, each of the eighty-six billion neurons in your brain, talks to other neurons by sending a tiny blip of voltage down a gossamer thin cable. We neuroscientists call that blip the spike. These tiny pulses of electricity stream endlessly, ceaselessly across your brain. Spikes are seeing, hearing, and feeling; thinking, planning, and doing. Spikes are how neurons talk to each other. And neurons talking to each other is how you do anything.

The uniquely human things you do are thanks to the chatter of spikes in your cortex ( So many in fact that we have to divide the cortex into a constellation of areas, each with its own name, to make sense of it all. (Few of these names are excitingthe area with the most neurons that talk directly to the spine, and so has the most control over movement, is called the primary motor cortex; the areas next door are the premotor cortex and, wait for it, the supplementary motor area. Inspired.) These areas all share the same types of neurons but do wildly different things with the spikes sent between them.

Many of these areas are dedicated to seeing, from the areas breaking down the world into its simplest componentsedges and lines and cornersto the areas dealing with motion, colors, objects, and faces. Some areas do hearing and touch; some control your movement.

There are areas for uniquely human things, like reading, speaking, and understanding the spoken word. And at the front of the cortex we find areas that do mysterious things with information from the outside world, somehow using it to plan, anticipate, and predict. All of it done by spikes.

The numbers are vertiginous. Of the eighty-six billion neurons in the adult human brain, about seventeen billion of those are found in the cortex. Each of those sends at most one spike per second, on average.

The United Nations tells us the expected lifespan of a human on this planet is about seventy years. Thats more than two billion seconds, each of which contains about seventeen billion spikes in cortex. All told, your lifespan is about thirty-four billion billion cortical spikes.

The cry you emitted on your appearance in the world. Your first tottering, uncertain steps. The pain when Susans wildly swinging arm knocked out your wobbly tooth in primary school. Recognizing that cluster of trees in the distance, and the relief of knowing youll now find your way across the damp, foggy hills back to the welcome warmth of the car. Plucking up the courage to ask for a date, and blurting it all out in a rush. The flush of embarrassment. The quiet euphoria of a yes. Deciding you just have to do something about the clash between the purple sofa and the lime green curtains. Remembering the smell of your moms bread and dads roast chicken. Cradling your baby. Reading this sentence. And this one.

All spikes.

From the magnificent to the mundane, everything youve done is in those thirty-four billion billion spikes that have streamed across your cortex. If I were to write the story of your life with one word for every spike, your biography would be longer than the combined length of all novels in English ever published. Yes, ever, since Gutenberg introduced movable type to Europe in 1439. And not just a bit longerseventy-six million times longer. Even with the combined efforts of Tom Wolfe, Neal Stephenson, and George R. R. Martin to deliver novels that are also handy for weighting down small children in a storm, novelists still have at least another 380 million years or so to publish as many words in English as spikes in your cortex in your lifetime. And below the cortex, billions upon billions more neurons, sending billions upon billions more spikes.

Youll excuse me if I attempt something a little less daunting.

In this book, Im going to tell you the story of just two of those seconds. Of a simple act: you spot that last cookie in the office tray, and thinkno one will mind if I take that, right?

A spikes journey from the eye that receives the light bouncing from the cookie, through the seeing parts of cortex turning patterns of light and shade into the edges, curves, crumbs, and colors of the cookie, on to cortical areas for perceiving, deciding, and remembering, plunging into the depths of the motor system, and out, out through the spine and on to the muscles, finally moving your hand to what your eye can see. A journey from seeing to deciding to moving, from eye to hand.

This is the story of everywhere the spike was sent, and of everything it saw on the waythe twinkling galaxy of neurons, the deep darkness of the cortex, the loneliest neuron. Of splitting into a thousand clones. Of spontaneous birth and instant death. An epic journey, all in but a moment of time, a story replayed two billion times over.