Got a bad memory? It’s actually much worse than you think, for the simple reason that you don’t know how much you have forgotten. I was at a school reunion not so long ago, and was shocked by my failure to remember many of the stories my old classmates told, even though I seemed to feature in many of them. For a while I feared that dementia was setting in, until I discovered that others failed to recognise some of the stories I told. I was consoled by one thing—the memory that some of my old mates were inveterate liars.
Memory, then, is highly selective. Nobody really knows the reasons why some memories stick and others don’t. Sigmund Freud suggested that memories of trauma are repressed, but this theory has not worn especially well. Survivors of the Holocaust, for example, seem to remember even the most horrific experiences. If anything, memories of emotional events are probably remembered better than those of mundane happenings. This is perhaps not surprising from an evolutionary viewpoint, since emotion generally signals happenings that bear, either positively or negatively, on future survival, and remembering emotional events may help us cope differently next time. ‘It’s a poor sort of memory that only works backwards,’ remarks the White Queen in Lewis Carroll’s Through the Looking-Glass, capturing the point that memory evolved not so much to provide a faithful record of the past as to help one deal with the future.
And even when we do remember past events, they are often remembered wrongly. The unreliability of eyewitness testimony is the bane of courts of law. There may even be survival value in altering our memories, perhaps to boost self-esteem or downplay past embarrassment. Politicians seem especially prone to memory tinkering. In his presidential campaigns, Ronald Reagan often spoke of wartime heroics, but the episodes he described actually came from old movies. Hillary Clinton told of landing in Bosnia in 1996 under sniper fire, but television records show her being greeted in peace by a smiling child. As Mark Twain once said, ‘I have been through some terrible things in my life, some of which actually happened.’
American psychologist Elizabeth Loftus, a pioneer of research on false memories, recounts a false memory of her own. She vividly recalls waking up one morning, at the age of fourteen, to find her mother dead in the swimming pool. In her mind she sees and smells cool pine trees, tastes iced tea and sees her mother in her nightgown, floating face down. She cries out in terror, starts screaming, sees the police cars with their lights flashing and the stretcher carrying her mother’s body. But she was in fact asleep when her mother’s body was discovered, not by her but by her Aunt Pearl. Loftus’s memory is a construction, built partly of her knowledge of what happened and partly of extra details supplied by her imagination.
Loftus found that false memories are easily implanted in memory. For example, she asked people to recall events such as being lost in a supermarket, or being taken for a ride in a hot-air balloon, and about a quarter of the people asked gave quite detailed accounts, even though the events had never actually occurred. Memories are also easily altered or implanted by persuasive questioning. In the 1980s some therapists created social mayhem by suggesting to their patients that their symptoms might be due to sexual abuse, often by a parent or close relative who was in fact innocent. This is not to say, of course, that sexual abuse does not occur or that all memories of abuse are false. Nevertheless, the events of that unfortunate decade, along with research by Loftus and others, have led to a better understanding that the probing of memory for past events needs to be undertaken with care, avoiding leading questions and presumptions of guilt. Our brains simply don’t work like cameras or tape recorders.
When we speak of memory, we usually mean memory for events or episodes in our personal lives. This is known as episodic memory, and distinguished from semantic memory, which is memory for enduring facts about the world—such as the memory that Wellington is the capital of New Zealand and that sugar tastes sweet. It includes all the words we know, and what they refer to. You probably know something like 50,000 words, along with associated objects, actions, qualities and the like.
In cases of amnesia, episodic memories are typically badly affected, while semantic memories remain more or less intact. One dramatic case is the English musician Clive Wearing, who suffered severe amnesia following a viral infection that destroyed part of his brain known as the hippocampus. Deprived of episodic memory, he lives in the present, constantly under the impression that he has just woken up, or risen from the dead. Yet he can talk, easily recognises his wife and can still play the piano and conduct a choir. His semantic memory appears to be largely intact.
Episodic memories are also profoundly affected in Alzheimer’s disease, which may affect up to 50 per cent of people over the age of 85. The disease attacks newer memories rather than older ones, so sufferers often seem to be mentally transported back into earlier periods in their lives. Again, the hippocampus is one of the areas targeted by the disease. But in at least one neurological condition, known as semantic dementia, it is semantic memory that is affected, while episodic memories remain surprisingly unimpaired. If that happens to me, I will have to cease writing essays of this sort, and will probably try to bore you instead with my autobiography. But be reassured, it probably won’t work because semantic memory also includes the power of language.