How could an experience, screen-based or otherwise, literally leave its mark on a sludgy brain? If we neuroscientists are to contribute anything significant at all to appreciating the effects of the digital lifestyle on our mental processing, it’s by pointing out the actual physical neuronal mechanisms at work: we should be able to demonstrate the causal link between exposure to certain environments and experiences, and ensuing thoughts and behavior. By understanding as much as possible about how the brain works, we’ll be able to get a much more accurate picture of how and to what extent screen technologies could be transformational.
The big challenge for neuroscience has always been to make the intellectual leap between a bit of brain tissue and a thought, an emotion—even a dream, in both senses of that word: the literal phenomenon of that bizarre inner world that unfolds during sleep, as well as the metaphor for planning wonderful outcomes for our lives. It’s a journey we’ll need to make in three steps: first, to find out how the brain itself works; second, to discover how it changes throughout life; and third, to see how these changes in the brain could amount to the “mind.” Yet it’s far from obvious even where to start.
“So how does the brain work, then?” The girl in front of me, probably about eleven years old, was insistent. Surely it was simply because I had run out of time in my one-hour talk to her group of schoolchildren that I had omitted to clear up this final, trivial question. We had looked at the brain from all angles by taking apart a plastic model. I had told my young audience about the time when I had been a student myself and had held a real human brain in my hands and, because brain tissue is nothing like the hard, bright pink plastic model but is creamy white, soft, and fragile, I had pondered what would have happened if some of it got caught under my fingernail. Can a memory or an emotion be dislodged by a fingernail? Could a bit of brain tissue that somehow related to a particular habit, such as biting your fingernails, actually end up adrift under a fingernail? How is the experience of being you, of seeing the world in a way no one else can share firsthand, generated by this unappealing and uncooperative mass that you can cup in one hand?
No model brain, nor indeed its real-life counterpart, offers any obvious starting point. There are no conspicuous moving parts, as there are for the heart or the lungs, that indicate what is going on. All you can do by looking at the brain is appreciate how, on the macro level, it is put together. You’ll see that there are enveloping layers around the top of the spinal cord as it swells out into the most basic part of the brain.1 From there evolution has added further compartments and easily discernible structures—brain regions that vary in size and importance according to the species. But the theme is the same for all mammals, whether you’re looking at the brain of a rat or of a human. You’ll always see, for example, a small cauliflower-like growth coming out from the back of the brain just above the spinal cord.2 You’ll also always see the two hemispheres that jam against each other like two fists, with their outer covering, the cortex (Latin for “bark”) wrapping around them the way bark wraps around a tree.3
The surface area of the cortex has expanded in humans to such an extent that accommodating such vast amounts of brain in the confines of the skull would be like accommodating a sheet of paper in a tight fist: you would have to crumple the paper up. In a sense, and so long as we don’t stretch the analogy too far, this is what evolution has done: the surface of the human brain is as wrinkled as a walnut, that of the other primates less so, that of cats and dogs even less still, and the cortex of rodents not at all. This thin outer layer is perhaps the most fascinating and enigmatic part of the brain. In evolutionary terms, it is the newest and, perhaps not surprisingly, the most prominent in humans, the species with the greatest intellectual capacity. So the cortex will feature more than any other brain area as we explore the impact on thinking of the digital technologies.
To get an idea of how the brain is put together, think of a busy metropolis such as New York City. The anatomically distinct brain regions would correspond to boroughs, within which would be districts and then neighborhoods—in brain terms, smaller and smaller groups of cells. By the time we arrive at a block, a street, or a line of houses, we are at the basic unit of neuronal communication: the gap (synapse) between any one brain cell and another. And the house on the street? That would be the neuron itself, the rooms within it the organelles, the specialized cellular parts that keep a single brain cell alive, just like any generic cell in the body. While this metaphor may convey the nested hierarchy of the anatomy of the brain areas, the extrapolation can go no further: it is simply a static snapshot of how the physical brain is built up.
In my talk to the young students, I had pried the plastic model apart and shown them all the different and easily discernible regions beneath, how they intertwined around each other, just as I had first seen in a real brain so long ago in the dissecting room of the Oxford University Anatomy Department. But would that answer satisfy the little girl standing in front of me, eyes like saucers, impatient for me to tell her in a sentence how the brain worked? The problem is that brain cells are less analogous to fixed structures such as bricks and houses, which don’t actually do anything, and more comparable to people, their highly dynamic inhabitants. What we really need, therefore, is an image, some kind of scenario that describes not only how the brain is constructed anatomically from the building blocks, the brain cells, but also how they actually function.
Neurons are the basic units of the brain, just as a person is the basic unit of an organization or a society. Like a person, a neuron is generic and yet at the same time an individual entity. A person changes gradually over time, and a neuron will also adapt. A neuron gradually makes connections across a small gap (the synapse) using an intermediary, a chemical messenger (a neurotransmitter); actual direct physical contact between brain cells is possible but features less. Similarly, a person gradually builds relations with others by indirect contact via a language; touching is rarer. With both chemical messengers and languages there’s enormous diversity but also an adherence to the same common principle: communication between two independent entities without any direct physical connection. Both languages and neurotransmitters come in a wide range of varieties, but they can be categorized into families, defined by geographical provenance (for language) or chemical structure (for a neurotransmitter). The actual mode of communication in both cases has parallels in that all languages and neurotransmitters can use a range of signals, from simple to complex and sophisticated. In the most basic scenario, a neuron can signal via its neurotransmitter a simple “yes” or “no,” which translates into a momentary inhibition or excitation of the activity of the target brain cell.
When a brain cell “speaks” (or more technically is “active”), it generates a small electrical blip4 lasting a thousandth of a second (a millisecond), which zooms down to the end of the cell to communicate with the next neuron.5 But there’s a problem once the electrical message reaches the synapse and can go no further. All is not lost, however: the arrival of the blip acts as a trigger for the tip of the cell to release its chemical messenger, which is able to travel across the synapse as readily as words travel through air. Once it reaches its destination, the next cell, the neurotransmitter enters into a molecular handshake with its special target.6 This interlocking is so tight and tailor-made that a better analogy might be a key fitting into a lock. The complexing of a neurotransmitter with its custom-made target triggers a brief change in voltage in the target cell, effectively a reconversion from a chemical signal to an electrical one. The “yes” in neuronal communication is when there is a momentary increase in electrical activity (excitation); the “no” is when activity is suppressed (inhibition).
Just as most of the time verbal communication is more than a simple monosyllable, with syllables ordered into words, words into sentences, and sentences into a statement, so it is with neurotransmitters: the final effect depends on the sequencing of different neurotransmitters converging over a particular period of time onto a given cell. In both cases the impact of each word or neurotransmitter signal will depend on the wider context over the period within which it occurs.7 Then, as milliseconds turn to seconds, to minutes, to hours, and eventually to days, the connections effected by this process—the connections between people or between neurons—change.
It’s quite fun, and indeed insightful, to explore the various parallels between personal relations and the paths these signals trace through the brain and personal relations: both strengthen through repeated use, becoming stronger and more intense. For both people and neurons, relationships are most flexible when young. Like people, neurons become increasingly specialized and more “individual” as their network grows. Over time, just as people mature and develop particular personality traits, neurons become more resistant to change in general function. And in the same way that friendships wither if they are not actively maintained, underused neuronal connections atrophy.
As an individual grows, he or she establishes more and more complex relationships, some close and frequent, others less activated and more distant; larger and larger groups eventually interconnect and form a still wider society. So it is with the brain, where a nested hierarchy of ever more complex layers of networks of neurons eventually make up a particular macro brain structure. All brain regions eventually interconnect with each other, even over long brain distances, via fiber tracts that operate something like telephone lines, enabling incessant dialogues all over the brain. It is a holistic organization.
The “bottom-up” approach to studying the brain explores just how this organization comes about. If you’re a neuroscientist specializing in understanding neurotransmitters, receptors, and how synapses operate, it’s a bit like being an expert in interpersonal communication. For example, the neurotransmitter dopamine is linked to many different brain processes, including arousal, addiction, reward, and initiation of movement. But for a bottom-up understanding of how chemicals such as dopamine function, we also need a top-down approach, one that starts with the macro brain areas and attempts to map out how they work together to give rise to different behaviors and ways of thinking.8 This time an appropriate analogy might be sociology or anthropology, either of which focuses on collective trends and outcomes rather than on the behavior of individuals.
Scientists are now using brain scans to image the wholesale activity of different brain areas as a result of different types of inputs, environments, and behaviors. In a brain scan you might see bright blobs pinpointing certain areas in a sea of gray brain, or perhaps multicolored arrays where white is a hot spot, shading through yellow, orange, and red to a low-activity purple-colored perimeter. But in the enigmatic cohesion of the brain, all the ongoing chatter between the various brain regions will actually not be visible to you. The images of a brain scan reveal the brain at work over a protracted period. Such scans usually have a resolution of seconds (in the very latest developments, tens of milliseconds), but the universal electrical signature of brain cells at work, the action potential, is a hundred or so times faster than that. Brain scans are like old Victorian photographs that show static buildings but exclude any people or animals, which would have been moving too fast for the exposure time. The buildings are perfectly real, but they don’t constitute the whole picture.
When looking at brain scans, it is also tempting to think that if a certain area of the brain lights up, it must be the center for whatever behavior or response is being studied. This notion of “centers” of the brain for this or that is attractive: moreover, if it were true, the brain would be so much easier to understand. Back on the cusp of the nineteenth century, Franz Gall introduced the “science” of phrenology (literally “study of the mind”). The white china heads covered with black-lined rectangles labeled with, for example, “love of country” or “love of children” were intended to provide the template against which the bumps of the individual head being studied could be compared to ascertain the strength of a trait. While these busts remain popular with photographers as a prop to enliven shots of media-worthy brain scientists, the approach inevitably was discredited as systematic examination of the brain itself became possible. But traces of the crazy rationale of phrenology, of there being multiple mini-brains within your head, can still fuel interpretations of real scientific findings.
The idea of “one brain area, one function” gained traction as medicine blossomed and clinicians became increasingly skilled at keeping patients alive despite dramatic brain damage from, say, a bullet, an injury, or a stroke. This is where a phrenology-like interpretation was able still to sneak in, by ascribing to the damaged brain area the “function” that had been lost. Yet, as one psychologist remarked more than half a century ago, if you remove a vacuum tube from a radio (yes, the analogy is that old) and the device started to howl, you wouldn’t claim the function of the tube was to inhibit howling. If the brain area in question malfunctions, like the elderly vacuum tube, the holistic system of the brain will be impaired, but the contribution of the brain region cannot be extrapolated backward from the final net outcome. To use another analogy, if a spark plug malfunctions, your car will not start, but you can’t deduce how a car works by studying a spark plug. We now know that there is no one function controlled by any one brain area. Vision, for example, involves dividing up different aspects of seeing form, motion, and color between as many as thirty different brain areas. And no one brain area has only one function. Rather, each brain structure contributes to a net final function not as a hierarchy but more in the way the various instruments in an orchestra produce a symphony.9
This processing in the brain will determine how you see the world, but whatever external inputs are being fed into your brain at any given time, the experience of that very moment will simultaneously change that organization of brain cells, and hence your thinking. One leading expert in brain development, Bryan Kolb, sums up: “Anything that changes your brain, changes who you will be. Your brain is produced not just by your genes; it’s sculpted by a lifetime of experiences. Experience alters brain activity, which changes gene expression. Any behavioral changes you see reflect alterations in the brain. The opposite is also true: behavior can change the brain.”10 And that is just what we’re going to explore next.