When you tell people you have a ‘bad memory’, that would seem to imply that there is only one ‘type’ of memory that can either be good or bad. This seems to look at memory as a binary thing and suggest that there’s no way you can have a memory that is good in some scenarios and bad in others.
In reality though, memory is much more complicated than that and really comes in a wide variety of flavors and varieties. For instance, you might have a very good short term memory or a very bad memory for faces – they’re not the same thing at all!
One particularly interesting type of memory with that in mind, is ‘episodic memory’. In many ways, this is the most important type of memory of all and could even be considered a crucial part of what makes you you. But what exactly is this type of memory? And how does it work?
Episodic Memory Explained
Basically, episodic memory is the memory you have about events. These are your unique recollections of things that happened in your life and things that you know to have happened in the lives of others. If you think of your brain as containing a large timeline, your episodic memory would then be responsible for that timeline and all the events that exist on it.
Often, episodic memory will get confused with autobiographical memory, which is understandable. Autobiographical memory refers to your memories of your own life, as well as facts about yourself. Some aspects of autobiographical memory to fall under the banner of episodic memory and vice versa then, but they are still two distinct things. For instance, autobiographical memory can also include facts about yourself – such as the city you were born in and your name. These are examples of ‘semantic memories’. Likewise, episodic memory can include information about other people, which is not in any way autobiographical. There is a fuzzy line to be drawn here however and the distinction is not quite perfect.
How Episodic Memories Are Formed
Encoding is what we consider the first crucial step in the formation of any memory. Here, the memory is converted to a construct to be stored within the brain’s long or short term memory.
The way this actually works on a physiological level is highly complex and not fully understood, though what we do know is fascinating.
Essentially, when you experience anything, this causes neurons to fire in your brain corresponding to what you’ve seen and heard. At the same time, the event will have an emotional content which is what defines the release of neurotransmitters and hormones. These tell us whether the event is happy or sad, as well as whether the event is important enough to be moved to the long-term memory for permanent storage.
What’s amazing, is the brain’s ability to take all the inputs from the sensory areas of the brain and then combine them into a single experience in the hippocampus. The hippocampus will then ultimately dictate on whether the inputs should be committed to long-term memory or not. Cases of anterograde amnesia – where patients lose the ability to formulate new memories – demonstrate to us the role of the hippocampus which is normally damaged (1).
Memories will often be stored primarily through particular types of encoding – meaning that they will rely more on one of the senses than the others. Most common for episodic memories is ‘semantic encoding’ meaning that the memory is based more on the meaning and our understanding of it, rather than the sound (acoustic encoding) or what we saw (visual encoding); although these might also play a role.
Memories can also be ‘consolidated’ as we recall them repeatedly. The more often we relive a memory in our brains, the more deeply encoded it will become. This likely occurs through the process known as myelination and long-term potentiation. Essentially, repeated use of any neural pathway will cause the myelin sheath that covers it to become stronger, thereby providing additional insulation and making the connection stronger.
The Fallibility of Your Episodic Memory
Interestingly, it has been proven on many occasion that our episodic and autobiographical memories are far from infallible and can be very easily misled. Simple leading questions for example can be enough to throw an honest jury – if a lawyer asks whether the witnesses saw the vehicle ‘slam’ into the one in front, they will estimate its speed as being higher than if the question uses the word ‘tap’.
Moreover, it appears that our memories can be edited through the simple act of retrieving them (see this article).
And of course the initial formation of the memory is also highly dependent on our attention and on our subjective interpretation of events. If something happens but your attention is not on the key event, then your memory might be very different from someone else who was more focussed at the time. What’s more, is that we will often ‘fill in the blanks’ with what we call ‘schemas’. In other words, we have a kind of ‘default’ idea of what certain items look like or what people behave like. If we weren’t fully paying attention, then often our brains will actually fill in the missing pieces by ‘guessing’ and we won’t know the difference!
One other interesting phenomenon pertaining to episodic memory is something called a ‘flashbulb memory’. This is a type of memory that is cemented in stone and is easy for us to vividly recall in extreme detail. Usually, flashbulb memories occur when we’re highly shocked, scared, happy or upset. This triggers a sudden rush of hormones and neurotransmitters corresponding to that emotion – adrenaline for fear for example – and that in turn means that the memory gets laid down much more permanently and vividly. This is why so many people remember where they were the day Diana died for example and why you probably remember your wedding day in greater detail than Thursday three weeks ago.