days. I am supposed to be an average reasonable and intelligent young man. However, lately (I cannot recall when it started) I have been a victim of many unusual and irrational thoughts . . . After my death I wish that an autopsy would be performed on me to see if there is any visible physical disorder.
Whitman’s request was granted. After an autopsy, the pathologist reported that Whitman had a small brain tumor. It was about the size of a nickel, and it was pressing against a part of his brain called the amygdala, which is involved in fear and aggression. This small amount of pressure on the amygdala led to a cascade of consequences in Whitman’s brain, resulting in him taking actions that would otherwise be completely out of character. His brain matter had been changing, and who he was changed with it.
This is an extreme example, but less dramatic changes in your brain can alter the fabric of who you are. Consider the ingestion of drugs or alcohol. Particular kinds of epilepsy make people more religious. Parkinson’s disease often makes people lose their faith, while the medication for Parkinson’s can often turn people into compulsive gamblers. It’s not just illness or chemicals that change us: from the movies we watch to the jobs we work, everything contributes to a continual reshaping of the neural networks we summarize as us. So who exactly are you? Is there anyone down deep, at the core?
Am I the sum of my memories?
Our brains and bodies change so much during our life that – like a clock’s hour hand – it’s difficult to detect the changes. Every four months your red blood cells are entirely replaced, for instance, and your skin cells are replaced every few weeks. Within about seven years every atom in your body will be replaced by other atoms. Physically, you are constantly a new you. Fortunately, there may be one constant that links all these different versions of your self together: memory. Perhaps memory can serve as the thread that makes you who you are. It sits at the core of your identity, providing a single, continuous sense of self.
But there might be a problem here. Could the continuity be an illusion? Imagine you could walk into a park and meet your self at different ages in your life. There you are aged six; as a teenager; in your late twenties; mid-fifties; early seventies; all the way through your final years. In this scenario, you could all sit together and share the same stories about your life, teasing out the single thread of your identity.
Or could you? You all possess the name and history, but the fact is that you’re all somewhat different people, in possession of different values and goals. And your life’s memories might have less in common than expected. Your memory of who you were at fifteen is different to who you actually were at fifteen; moreover, you’ll have different memories that relate back to the same events. Why? Because of what a memory is – and isn’t.
Imagine a person could be split into herself at all her different ages. Would they all agree on the same memories? If not, are they really the same person?
Rather than memory being an accurate video recording of a moment in your life, it is a fragile brain state from a bygone time that must be resurrected for you to remember.
Here’s an example: you’re at a restaurant for a friend’s birthday. Everything you experience triggers particular patterns of activity in your brain. For example, there’s a particular pattern of activity sparked into life by the conversation between your friends. Another pattern is activated by the smell of the coffee; yet another by the taste of a delicious little French cake. The fact that the waiter puts his thumb in your cup is another memorable detail, represented by a different configuration of neurons firing. All of these constellations become linked with one another in a vast associative network of neurons that the hippocampus replays, over and over, until the associations become fixed. The neurons that are active at the same time will establish stronger connections between them: cells that fire together, wire together. The resulting network is the unique signature of the event, and it represents your memory of the birthday dinner.
Your memory of an event is represented by the unique constellation of cells involved in the details you experience.
Now let’s imagine that six months later you taste one of those little French cakes, just like the one you tasted at the birthday party. This very specific key can unlock the whole web of associations. The original constellation lights up, like the lights of a city switching on. And suddenly you’re back in that memory.
Although we don’t always realize it, the memory is not as rich as you might have expected. You know that your friends were there. He must have been wearing a suit, because he always wears a suit. And she was wearing a blue shirt. Or maybe it was purple? It might have been green. If you really probe the memory, you’ll realize that you can’t remember the details of any of the other diners at the restaurant, even though the place was full.
So your memory of the birthday meal has started to fade. Why? For a start, you have a finite number of neurons, and they are all required to multitask. Each neuron participates in different constellations at different times. Your neurons operate in a dynamic matrix of shifting relationships, and heavy demand is continually placed on them to wire with others. So your memory of the birthday dinner has become muddied, as those “birthday” neurons have been co-opted to participate in other memory networks. The enemy of memory isn’t time; it’s other memories. Each new event needs to establish new relationships among a finite number of neurons. The surprise is that a faded memory doesn’t seem faded to you. You feel, or at least assume, that the full picture is there.
And your memory of the event is even more dubious. Say that in the intervening year since the dinner, your two friends have split up. Thinking back on the dinner, you might now misremember sensing red flags. Wasn’t he more quiet than usual that night? Weren’t there moments of awkward silence between the two? Well, it will be difficult to know for certain, because the knowledge that’s in your network now changes the memory that corresponds to then. You can’t help but have your present color your past. So a single event may be perceived somewhat differently by you at different stages in your life.
The fallibility of memory
Clues to the malleability of our memory come from the pioneering work of Professor Elizabeth Loftus at University of California, Irvine. She transformed the field of memory research by showing how susceptible memories are.
Loftus devised an experiment in which she invited volunteers to watch films of car crashes, and then asked them a series of questions to test what they remembered. The questions she asked influenced the answers she received. She explains: “When I asked how fast were the cars going when they hit each other, versus how fast were the cars going when they smashed into each other, witnesses give different estimates of speed. They thought the cars were going faster when I used the word smashed.” Intrigued by the way that leading questions could contaminate memory, she decided to go further.
Would it be possible to implant entirely false memories? To find out, she recruited a selection of participants, and had her team contact their families to get information about events in their past. Armed with this information, the researchers put together four stories about each participant’s childhood. Three were true. The fourth story contained plausible information, but was entirely made up. The fourth story was about getting lost in a shopping mall as a child, being found by a kind elderly person, and finally being reunited with a parent.
In a series of interviews, participants were told the four stories. At least a quarter claimed they could remember the incident of being lost in the mall – even though it hadn’t actually happened. And it didn’t stop
