1 Where Is My Mind? why we remember some things and forget others. Maybe the reason my memory is so bad is that I always do at least two things at once. It''s easier to forget something you only half did or quarter did. --Andy Warhol Over your lifetime, you will be exposed to far more information than any organism could possibly store. According to one estimate, the average American is exposed to thirty-four gigabytes (or 11.8 hours'' worth) of information a day. With a near-constant stream of images, words, and sounds coming at us through our smartphones, the internet, books, radio, television, email, and social media, not to mention the countless experiences we have as we move through the physical world, it''s not surprising we don''t remember everything. On the contrary, it''s amazing that we remember anything.

To forget is to be human. Yet, forgetting is one of the most puzzling and frustrating aspects of the human experience. So it''s natural to ask, "Why do we remember some events and forget others?" Not long ago, Nicole and I celebrated the thirtieth anniversary of the year we met. To mark the occasion, we pulled out old family videos that had been gathering dust over the years and had them digitized. I was particularly fascinated by the footage of our daughter Mira''s birthday parties. As we watched the videos of Mira growing up, I expected them to trigger a flood of memories. Instead, I discovered that almost all of them seemed new to me. I was the one shooting the videos, yet I did not have the experience of recollecting these parties as individual events--except for one.

For most of her early childhood, we organized Mira''s birthday parties at such places as the Sacramento Zoo, the local science museum, a gymnastics studio, or an indoor rock-climbing gym. These venues ensure that the kids can be entertained and contained, with a steady stream of food, sugary drinks, and activities provided during the two-hour reserved window. At these birthday parties, I would participate in the festivities, but for the most part I focused on documenting these precious moments so that Nicole and I could revisit them later. The year Mira turned eight, I decided to try something different. When I was a kid, my brother, Ravi, and I celebrated our birthdays at home. We had a lot of fun, and our parents didn''t need to spend a lot of money. So, that year I followed my do-it-yourself punk-rock ethos and organized Mira''s party at our house. Anyone who has ever hosted a children''s birthday party knows the number one goal is to keep the kids busy.

Mira was always into art, so I found a shop in a nearby town that provided premade cat-shaped ceramics that the kids could paint with glaze and later have fired to take home. Between the craft activity and the SpongeBob SquarePants piñata I had hung up in the backyard, I figured I had it covered. I couldn''t have been more wrong. Roughly fifteen minutes into the activity, all the cats were painted. With hours left to fill before cake time, the children were getting restless, and I was beginning to panic. I herded the kids out to the backyard, where they lined up to take turns whacking a piñata that refused to burst. Eventually, I took matters into my own hands, got out a golf club from the garage, and bashed a hole in it. Candy went flying everywhere and the kids descended on that papier-m'ché SpongeBob like a scene from The Walking Dead.

I saw one kid launch herself like an Olympic gymnast across the yard to get to a Snickers Mini she''d spotted in the grass. It was still too early to bring out the cake, so I came up with the bright idea of having them play tug-of-war with an old rope I found in the garage. It had rained the day before, and the kids kept slipping and sliding around on the muddy grass. I remember looking around the backyard--some of the kids were chasing one another around in a sugar frenzy, one or two were complaining about rope burn, and a couple were taking turns beating the SpongeBob carcass to death with the golf club--and thinking how quickly an eight-year-old''s birthday party can go from painting ceramics to Lord of the Flies. It was not my finest moment, but it is one I remember in excruciating detail. Not all our experiences are of equal importance. Some are utterly unremarkable; others are moments we hope to treasure forever. Unfortunately, even priceless moments can sometimes slip through our fingers.

At the time, I could have sworn I would vividly remember each of Mira''s parties, so why is it that this one stands out and the other birthday videos seem like reruns from a distant TV show? How can an experience that feels so memorable while we''re living it ultimately be reduced to little more than a vague fragment of what transpired? Although we tend to believe that we can and should remember anything we want, the reality is we are designed to forget, which is one of the most important lessons to be taken from the science of memory. As we will explore in this chapter, as long as we are mindful of how we remember and why we forget, we can make sure to create memories for our most important moments that will stick around. making the right connections The scientific study of memory as we know it today was pioneered in the late nineteenth century by German psychologist Hermann Ebbinghaus. A cautious and methodical researcher, Ebbinghaus concluded that, to understand memory, we must first be able to quantify it objectively. Rather than asking people subjective questions about events such as their kid''s birthday parties, Ebbinghaus developed a new approach to quantify learning and forgetting. And unlike modern psychologists, who have the luxury of enlisting college students to voluntarily participate in their studies, poor Ebbinghaus worked alone. Like a mad scientist in a Gothic horror novel, he subjected himself to mind-numbing experiments, in which he memorized thousands of meaningless three-letter words called trigrams, each consisting of a vowel sandwiched between two consonants. His idea was that he could measure memory by counting the number of trigrams--e.

g., DAX, REN, VAB--he was able to successfully learn and retain. We should pause a moment to appreciate the painstaking work that went into Ebbinghaus''s studies. In his 1885 treatise, On Memory: A Contribution to Experimental Psychology, he writes that he could only memorize sixty-four trigrams in each forty-five-minute session because "toward the end of this time exhaustion, headache, and other symptoms were often felt." In the end, his Herculean efforts bore fruit, as his experiments revealed some of the most fundamental aspects about the way we learn and forget. One of his most important achievements was to construct a forgetting curve, allowing him to graph, for the first time, how quickly we forget information. Ebbinghaus discovered that only twenty minutes after memorizing a list of trigrams, he had forgotten nearly half of them. One day later, he had forgotten about two-thirds of what he originally learned.

Although there are some caveats to Ebbinghaus''s findings, his bottom line holds: Much of what you are experiencing right now will be lost in less than a day. Why? To answer this question, let''s begin by breaking down how a memory is formed in the first place. Every area of the human neocortex, the densely folded mass of gray tissue on the outside of the brain, consists of massive populations of neurons--86 billion, according to one estimate. To put this number into perspective, that''s more than ten times the human population of the earth. Neurons are the most basic working unit of the brain. These specialized cells are responsible for carrying messages to different areas of the brain about the sensory information we take in from the world. Everything we feel, see, hear, touch, and taste, every breath we take, every move we make (sorry, couldn''t help myself), happens because of communication between neurons. If you feel yourself falling in love, if you''re angry, or if you''re slightly hungry, that''s the outcome of neurons talking to one another.

Neurons can also work in the background to handle important functions we''re not even aware of, such as keeping our hearts pumping. They even work while we''re sleeping, filling our heads with crazy dreams. Neuroscientists are still working out exactly how all these neurons work together, but the knowledge we have so far is enough to build computer models that capture some of the basic principles that govern brain function. In essence, neurons function like a democracy. Just as one person has only one vote to influence the outcome of an election, a single neuron plays only a small role in any kind of neural computation. In a democracy, we form political alliances to advance our individual agendas, and neurons form similar alliances to get things done in the brain. The Canadian neuroscientist Donald Hebb, whose work was influential to our understanding of how neurons contribute to learning, called these alliances cell assemblies. In neuroscience, as in politics, it''s all about having the right connections.

To get a better sense of how this works, let''s consider what happens as a newborn baby is exposed to human speech. Before a language is learned, babies can hear differences between sounds, but they don''t know how to parse those sounds in a linguistically meaningful way. Fortunately, from the moment we are born, our brains get to work making sense of what we are hearing, trying to break up a continuous stream of sound waves into discrete syllables. What the baby ultimately perceives will depend on an election taking place in areas of the brain that.