A familiar scenario in films and novels has a character who stumbles into the action, with no knowledge of who they are (Memento, anyone?). Suffering from amnesia, the person has a lack of memory relating to personal events and information from their past. Yet, sit this person down at the dining table and they still possess the knowledge of how to feed themselves, which hand to use for knife and fork, what the food items are, and so forth. Strange, isn’t it?
But it wouldn’t just be eating. Had they learned it before the amnesia struck, they would be able to tell you that the Nile is located in Africa, or that Abraham Lincoln was the sixteenth American president. This ability to remember is owing to the multifaceted nature of memory.
Your memory is made of many parts
Our memory is not a single, unitary thing, but rather consists of different divisions. Just as you might be better at one sport than another, or a good cook but a disastrous baker, you might be stronger in one form of memory than another. Your memory for dates, birthdays, and other stark facts and figures is what is known as your semantic memory. Items in semantic memory are divorced from context, so whilst you might be able to remember the names of all six of Henry VIII’s wives, you are unlikely to remember the context in which you learned them – where you were or how you felt at the time. Many people find rote learning and repetition of information an effective way to store and later retrieve this information.
Semantic memory is different to our memory for the events that are personal to our own lives – the form of memory you might draw upon when you remember what you did last weekend or on a recent holiday. This is known as episodic memory. Rather than isolated facts, episodic memories are associated with a specific context or situation. So when you call up an item in episodic memory, it comes complete with a time and place, as well as associated emotions. You might relive the joy you felt upon receiving an award or the distress or fear of a negative event. Remembering where you left your keys requires conjuring up this richer form of memory.
Importantly, the more you think about an event stored in episodic memory – a process known as rehearsal – the more strongly that item becomes represented in your long-term episodic storage, i.e. the more you relive an event, the longer it will stay with you. There is much debate amongst researchers over whether this is due to creating more pathways in the brain to retrieve that item, more mental representations of that item, or some other factor(s). Whatever the reason may be, memories that have occurred further in the past are often rehearsed more frequently. Think about your family’s anecdotes – there are always some stories everyone knows off by heart, simply because they are retold at every family gathering!
Time and tide wash away your memories
This all means that recent events are likely to be more weakly stored in your memory than those in the more distant past. But time also plays another role in what information you remember and what you forget. With the passage of time, information can be lost or altered – a process called ‘decay’. This decay is most prominent in the first few days after the acquisition of information; therefore details such as where you have put your keys are most easily lost immediately after the event. After this initial loss, there is a much smaller loss of information – a process termed transience. So once information has successfully avoided the decay of that initial ‘danger period’, and successfully made it into your long-term memory store, it is more likely to avoid being forgotten.
To explain a little further, information we receive is processed and introduced, or ‘encoded’, into your memory store. Information or experiences are initially processed in short-term memory – a temporary store that is highly subject to disruption. From short-term memory, some information that is deemed important or relevant enough, is transferred into long-term memory. This is permanent and far more stable than short-term memory. So while your long-term memories aren’t infallible (they can be altered by new information – but that’s a different story!), once information is stored in your long-term memory, you are far more likely to remember it in future.
Finally, and importantly, emotion can strengthen the representation and retrieval of episodic memories. Where you put your keys is unlikely to be associated with much, if any, emotion (even though trying to find them later on might be associated with increasing anxiety!). The recent and unemotional nature of putting your keys on the kitchen worktop conspire to make “where did I put my keys?” an easily forgettable thing; whereas, all that repetition during your school days may just ensure that you never forget which year the Magna Carta was signed.
Now, when was that again…?
Answer by Stephanie Baines