Most experiences float by unrecorded, but some erected more lasting impressions. When an experience creates a particularly strong or enduring pattern of neuronal activity, it becomes etched on the brain – and memory is formed.
Laying down a memory can be a deliberate ace, particularly when there is a certainty that the information will be needed again. Still, most episodes and facts are encoded without any apparent effort. Why is it that some ideas and events become part of the mind’s furniture while millions of others are forgotten or merely submerged in our pool of general knowledge?
The durability of an episodic memory depends on how exciting the original experience ·was or how excited the individual’s brain was when it occurred. It also depends, much like the memory of a factor a piece of information, on how much attention was paid to it and how often it is recalled.
Every experience we have is produced by neurons in the brain firing in a particular pattern. When something is very impressive, or if a person’s brain is fired up with excitement, the neurons participating in the experience fire fast and furiously. Trus encourages the formation of links between the neurons, which makes them more likely to fire together again in future. When they fire again, and the same (or a very similar) pattern recurs, the person experiences a replay of the original experience – in other words, a memory.
Changing contexts
Although recollection involves a replay of experience, the re-run is never precisely the same as the original because each time a memory is triggered, it occurs in a new context – the context of what is happening in the brain when the memory is revived. Imagine that you taste some exotic fruit such as a kumquat for the first time on holiday. The next time you taste a kumquat, it will bring to mind a memory of the holiday because the kumquat experience is linked to the context in which it occurred. However, your second tasting will also be associated with what is happening then and there – a dinner party, perhaps – and from then onwards, memories of kumquats will have echoes of both experiences. In this way, memories are elaborated upon and altered whenever they are recalled.
The ever-changing nature of Memories means that no two people ever have the same recollection of a past event – even if they had the experience at the time. For example, if a couple sees a film. Together, they may leave the cinema with similar memories of it. However, as these recollections become associated in each person’s mind with new experiences, they may start to diverge. In a later discussion, there might be disagreement about some of the details from the film – which could be resolved by watching it again. But most experiences are not recorded on celluloid, which is why people who argue 1bo ut shared events may never resolve the disputes that arise as a result of altered memories.
A Memory Full Of Surprises
Researchers have found that people are particularly good at remembering anything that comes as a surprise. In other words, if you experience something that is out of line with your expectations, it can become deeply embedded in your memory.
For example, if you went into a bank and saw all the usual things clerks, customers, and money – it would probably meld with all your other memories of trips to the bank and eventually disappear. But if you went into a bank and saw a walrus waiting in line, this visit would become firmly fixed in your mind. Why? Because queuing up with a walrus totally violates your idea of what should be happening in a bank. This tendency for surprising information to be remembered is sometimes called the Von Restoroff effect after the psychologist who first described the phenomenon.
Creating Permanent Bonds
Every time a particular set of neurons fire together, they become more likely to fire together in future. When connections are repeatedly activated, they form even more robust links that bind them into a single unit – a process called long-term potentiation. This is important in forming long-term memories.
- If neuron A receives a stimulus that causes it to fire strongly, it will pass the signal to neighbouring neuron B and, in the process, cause changes to neuron B that make it more responsive to neuron A in future.
- Each time the two neurons fire together, the link between them strengthens until they are so closely bonded that they invariably fire together.
- When neurons A and B fire together, their combined strength is enough to activate another neuron, C, which is weakly linked to both of them.
- With repeated firing, all three cells undergo changes that forge links between them and become bound together in a pattern. A permanent memory has been formed.
