The Shallows

by Nicholas Carr

  The next challenge facing Kandel was to figure out how such briefly held short-term memories could be transformed into much more permanent long-term memories. What was the molecular basis of the consolidation process? Answering that question would require him to enter the realm of genetics.

  In 1983, the prestigious and well-financed Howard Hughes Medical Institute asked Kandel, together with Schwartz and the Columbia University neuroscientist Richard Axel, to head a research group in molecular cognition, based at Columbia. The group soon succeeded in harvesting neurons from larval Aplysia and using them to grow, as a tissue culture in the laboratory, a basic neural circuit incorporating a presynaptic neuron, a postsynaptic neuron, and the synapse between them. To mimic the action of the modulating interneurons, the scientists injected serotonin into the culture. A single squirt of serotonin, replicating a single learning experience, triggered, as expected, a release of glutamate—producing the brief strengthening of the synapse that is characteristic of short-term memory. Five separate squirts of serotonin, in contrast, strengthened the existing synapse for days and also spurred the formation of new synaptic terminals—changes characteristic of long-term memory.

  What happens after repeated injections of serotonin is that the enzyme kinase A, along with another enzyme, called MAP, moves from the neuron’s outer cytoplasm into its nucleus. There, kinase A activates a protein called CREB-1, which in turn switches on a set of genes that synthesize the proteins the neuron needs to grow new synaptic terminals. At the same time, MAP activates another protein, CREB-2, which switches off a set of genes that inhibit the growth of new terminals. Through a complex chemical process of cellular “marking,” the resulting synaptic changes are concentrated at particular regions on the surface of the neuron and perpetuated over long periods of time. It is through this elaborate process, involving extensive chemical and genetic signals and changes, that synapses become able to hold memories over the course of days or even years. “The growth and maintenance of new synaptic terminals,” writes Kandel, “makes memory persist.”21 The process also says something important about how, thanks to the plasticity of our brains, our experiences continually shape our behavior and identity: “The fact that a gene must be switched on to form long-term memory shows clearly that genes are not simply determinants of behavior but are also responsive to environmental stimulation, such as learning.”22

  THE MENTAL LIFE of a sea slug, it seems safe to say, is not particularly exciting. The memory circuits that Kandel and his team studied were simple ones. They involved the storage of what psychologists call “implicit” memories—the unconscious memories of past experiences that are recalled automatically in carrying out a reflexive action or rehearsing a learned skill. A slug calls on implicit memories when retracting its gill. A person draws on them when dribbling a basketball or riding a bike. As Kandel explains, an implicit memory “is recalled directly through performance, without any conscious effort or even awareness that we are drawing on memory.”23

  When we talk about our memories, what we’re usually referring to are the “explicit” ones—the recollections of people, events, facts, ideas, feelings, and impressions that we’re able to summon into the working memory of our conscious mind. Explicit memory encompasses everything that we say we “remember” about the past. Kandel refers to explicit memory as “complex memory”—and for good reason. The long-term storage of explicit memories involves all the biochemical and molecular processes of “synaptic consolidation” that play out in storing implicit memories. But it also requires a second form of consolidation, called “system consolidation,” which involves concerted interactions among far-flung areas of the brain. Scientists have only recently begun to document the workings of system consolidation, and many of their findings remain tentative. What’s clear, though, is that the consolidation of explicit memories involves a long and involved “conversation” between the cerebral cortex and the hippocampus.

  A small, ancient part of the brain, the hippocampus lies beneath the cortex, folded deep within the medial temporal lobes. As well as being the seat of our navigational sense—it’s where London cabbies store their mental maps of the city’s roads—the hippocampus plays an important role in the formation and management of explicit memories. Much of the credit for the discovery of the hippocampus’s connection with memory storage lies with an unfortunate man named Henry Molaison. Born in 1926, Molaison was stricken with epilepsy after suffering a severe head injury in his youth. During his adult years, he experienced increasingly debilitating grand mal seizures. The source of his affliction was eventually traced to the area of his hippocampus, and in 1953 doctors removed most of the hippocampus as well as other parts of the medial temporal lobes. The surgery cured Molaison’s epilepsy, but it had an extraordinarily strange effect on his memory. His implicit memories remained intact, as did his older explicit memories. He could remember the events of his childhood in great detail. But many of his more recent explicit memories—some dating back years before the surgery—had vanished. And he was no longer able to store new explicit memories. Events slipped from his mind moments after they happened.

  Molaison’s experience, meticulously documented by the English psychologist Brenda Milner, suggested that the hippocampus is essential to the consolidation of new explicit memories but that after a time many of those memories come to exist independently of the hippocampus.24 Extensive experiments over the last five decades have helped untangle this conundrum. The memory of an experience seems to be stored initially not only in the cortical regions that record the experience—the auditory cortex for a memory of a sound, the visual cortex for a memory of a sight, and so forth—but also in the hippocampus. The hippocampus provides an ideal holding place for new memories because its synapses are able to change very quickly. Over the course of a few days, through a still mysterious signaling process, the hippocampus helps stabilize the memory in the cortex, beginning its transformation from a short-term memory into a long-term one. Eventually, once the memory is fully consolidated, it appears to be erased from the hippocampus. The cortex becomes its sole holding place. Fully transferring an explicit memory from the hippocampus to the cortex is a gradual process that can take many years.25 That’s why so many of Molaison’s memories disappeared along with his hippocampus.

  The hippocampus seems to act as something like an orchestra conductor in directing the symphony of our conscious memory. Beyond its involvement in fixing particular memories in the cortex, it is thought to play an important role in weaving together the various contemporaneous memories—visual, spatial, auditory, tactile, emotional—that are stored separately in the brain but that coalesce to form a single, seamless recollection of an event. Neuroscientists also theorize that the hippocampus helps link new memories with older ones, forming the rich mesh of neuronal connections that give memory its flexibility and depth. Many of the connections between memories are likely forged when we’re asleep and the hippocampus is relieved of some of its other cognitive chores. As the psychiatrist Daniel Siegel explains in his book The Developing Mind, “Though filled with a combination of seemingly random activations, aspects of the day’s experiences, and elements from the distant past, dreams may be a fundamental way in which the mind consolidates the myriad of explicit recollections into a coherent set of representations for permanent, consolidated memory.”26 When our sleep suffers, studies show, so, too, does our memory.27

  Much remains to be learned about the workings of explicit and even implicit memory, and much of what we now know will be revised and refined through future research. But the growing body of evidence makes clear that the memory inside our heads is the product of an extraordinarily complex natural process that is, at every instant, exquisitely tuned to the unique environment in which each of us lives and the unique pattern of experiences that each of us goes through. The old botanical metaphors for memory, with their emphasis on continual, indeterminate organic growth, are, it turns out, remarkably apt. In fact, they seem
to be more fitting than our new, fashionably high-tech metaphors, which equate biological memory with the precisely defined bits of digital data stored in databases and processed by computer chips. Governed by highly variable biological signals, chemical, electrical, and genetic, every aspect of human memory—the way it’s formed, maintained, connected, recalled—has almost infinite gradations. Computer memory exists as simple binary bits—ones and zeros—that are processed through fixed circuits, which can be either open or closed but nothing in between.

  Kobi Rosenblum, who heads the Department of Neurobiology and Ethology at the University of Haifa in Israel, has, like Eric Kandel, done extensive research on memory consolidation. One of the salient lessons to emerge from his work is how different biological memory is from computer memory. “The process of long-term memory creation in the human brain,” he says, “is one of the incredible processes which is so clearly different than ‘artificial brains’ like those in a computer. While an artificial brain absorbs information and immediately saves it in its memory, the human brain continues to process information long after it is received, and the quality of memories depends on how the information is processed.”28 Biological memory is alive. Computer memory is not.

  Those who celebrate the “outsourcing” of memory to the Web have been misled by a metaphor. They overlook the fundamentally organic nature of biological memory. What gives real memory its richness and its character, not to mention its mystery and fragility, is its contingency. It exists in time, changing as the body changes. Indeed, the very act of recalling a memory appears to restart the entire process of consolidation, including the generation of proteins to form new synaptic terminals.29 Once we bring an explicit long-term memory back into working memory, it becomes a short-term memory again. When we reconsolidate it, it gains a new set of connections—a new context. As Joseph LeDoux explains, “The brain that does the remembering is not the brain that formed the initial memory. In order for the old memory to make sense in the current brain, the memory has to be updated.”30 Biological memory is in a perpetual state of renewal. The memory stored in a computer, by contrast, takes the form of distinct and static bits; you can move the bits from one storage drive to another as many times as you like, and they will always remain precisely as they were.

  The proponents of the outsourcing idea also confuse working memory with long-term memory. When a person fails to consolidate a fact, an idea, or an experience in long-term memory, he’s not “freeing up” space in his brain for other functions. In contrast to working memory, with its constrained capacity, long-term memory expands and contracts with almost unlimited elasticity, thanks to the brain’s ability to grow and prune synaptic terminals and continually adjust the strength of synaptic connections. “Unlike a computer,” writes Nelson Cowan, an expert on memory who teaches at the University of Missouri, “the normal human brain never reaches a point at which experiences can no longer be committed to memory; the brain cannot be full.”31 Says Torkel Klingberg, “The amount of information that can be stored in long-term memory is virtually boundless.”32 Evidence suggests, moreover, that as we build up our personal store of memories, our minds become sharper. The very act of remembering, explains clinical psychologist Sheila Crowell in The Neurobiology of Learning, appears to modify the brain in a way that can make it easier to learn ideas and skills in the future.33

  We don’t constrain our mental powers when we store new long-term memories. We strengthen them. With each expansion of our memory comes an enlargement of our intelligence. The Web provides a convenient and compelling supplement to personal memory, but when we start using the Web as a substitute for personal memory, bypassing the inner processes of consolidation, we risk emptying our minds of their riches.

  In the 1970s, when schools began allowing students to use portable calculators, many parents objected. They worried that a reliance on the machines would weaken their children’s grasp of mathematical concepts. The fears, subsequent studies showed, were largely unwarranted.34 No longer forced to spend a lot of time on routine calculations, many students gained a deeper understanding of the principles underlying their exercises. Today, the story of the calculator is often used to support the argument that our growing dependence on online databases is benign, even liberating. In freeing us from the work of remembering, it’s said, the Web allows us to devote more time to creative thought. But the parallel is flawed. The pocket calculator relieved the pressure on our working memory, letting us deploy that critical short-term store for more abstract reasoning. As the experience of math students has shown, the calculator made it easier for the brain to transfer ideas from working memory to long-term memory and encode them in the conceptual schemas that are so important to building knowledge. The Web has a very different effect. It places more pressure on our working memory, not only diverting resources from our higher reasoning faculties but obstructing the consolidation of long-term memories and the development of schemas. The calculator, a powerful but highly specialized tool, turned out to be an aid to memory. The Web is a technology of forgetfulness.

  WHAT DETERMINES WHAT we remember and what we forget? The key to memory consolidation is attentiveness. Storing explicit memories and, equally important, forming connections between them requires strong mental concentration, amplified by repetition or by intense intellectual or emotional engagement. The sharper the attention, the sharper the memory. “For a memory to persist,” writes Kandel, “the incoming information must be thoroughly and deeply processed. This is accomplished by attending to the information and associating it meaningfully and systematically with knowledge already well established in memory.”35 If we’re unable to attend to the information in our working memory, the information lasts only as long as the neurons that hold it maintain their electric charge—a few seconds at best. Then it’s gone, leaving little or no trace in the mind.

  Attention may seem ethereal—a “ghost inside the head,” as the developmental psychologist Bruce McCandliss says36 —but it’s a genuine physical state, and it produces material effects throughout the brain. Recent experiments with mice indicate that the act of paying attention to an idea or an experience sets off a chain reaction that crisscrosses the brain. Conscious attention begins in the frontal lobes of the cerebral cortex, with the imposition of top-down, executive control over the mind’s focus. The establishment of attention leads the neurons of the cortex to send signals to neurons in the midbrain that produce the powerful neurotransmitter dopamine. The axons of these neurons reach all the way into the hippocampus, providing a distribution channel for the neurotransmitter. Once the dopamine is funneled into the synapses of the hippocampus, it jump-starts the consolidation of explicit memory, probably by activating genes that spur the synthesis of new proteins.37

  The influx of competing messages that we receive whenever we go online not only overloads our working memory; it makes it much harder for our frontal lobes to concentrate our attention on any one thing. The process of memory consolidation can’t even get started. And, thanks once again to the plasticity of our neuronal pathways, the more we use the Web, the more we train our brain to be distracted—to process information very quickly and very efficiently but without sustained attention. That helps explain why many of us find it hard to concentrate even when we’re away from our computers. Our brains become adept at forgetting, inept at remembering. Our growing dependence on the Web’s information stores may in fact be the product of a self-perpetuating, self-amplifying loop. As our use of the Web makes it harder for us to lock information into our biological memory, we’re forced to rely more and more on the Net’s capacious and easily searchable artificial memory, even if it makes us shallower thinkers.

  The changes in our brains happen automatically, outside the narrow compass of our consciousness, but that doesn’t absolve us from responsibility for the choices we make. One thing that sets us apart from other animals is the command we have been granted over our attention. “‘Learning how to think’ really means lear
ning how to exercise some control over how and what you think,” said the novelist David Foster Wallace in a commencement address at Kenyon College in 2005. “It means being conscious and aware enough to choose what you pay attention to and to choose how you construct meaning from experience.” To give up that control is to be left with “the constant gnawing sense of having had and lost some infinite thing.”38 A mentally troubled man—he would hang himself two and a half years after the speech—Wallace knew with special urgency the stakes involved in how we choose, or fail to choose, to focus our mind. We cede control over our attention at our own peril. Everything that neuroscientists have discovered about the cellular and molecular workings of the human brain underscores that point.

  Socrates may have been mistaken about the effects of writing, but he was wise to warn us against taking memory’s treasures for granted. His prophecy of a tool that would “implant forgetfulness” in the mind, providing “a recipe not for memory, but for reminder,” has gained new currency with the coming of the Web. The prediction may turn out to have been merely premature, not wrong. Of all the sacrifices we make when we devote ourselves to the Internet as our universal medium, the greatest is likely to be the wealth of connections within our own minds. It’s true that the Web is itself a network of connections, but the hyperlinks that associate bits of online data are nothing like the synapses in our brain. The Web’s links are just addresses, simple software tags that direct a browser to load another discrete page of information. They have none of the organic richness or sensitivity of our synapses. The brain’s connections, writes Ari Schulman, “don’t merely provide access to a memory; they in many ways constitute memories.”39 The Web’s connections are not our connections—and no matter how many hours we spend searching and surfing, they will never become our connections. When we outsource our memory to a machine, we also outsource a very important part of our intellect and even our identity. William James, in concluding his 1892 lecture on memory, said, “The connecting is the thinking.” To which could be added, “The connecting is the self.”