What did you do yesterday? Are you sure? How do you know?
We tend to trust our memories, and those of other people, but actually, these are fairly unreliable.
Now, I think I can remember things from when I was very small. For example, I remember when my brother (2 years younger than me) was born, because Granny came round the next day, and everyone seemed to be in a bad mood (lots I could add here!) I also remember that his cot was put into my room at some point, and that I tried to pinch him to make him cry, but my arms were slightly too chubby for the gaps between the cot bars, and I couldn’t reach him, and I hurt my arms trying. . .I remember Aunty Jenny coming to peel vegetables when my mum was in hospital, and she sat me on the draining board to watch her. . I remember Paul Wong (a family friend) holding me by my ankles and spinning me round, and I disliked him intensely.
However, my son (the scientist) tells me that all this is untrue—or at least unreliable. He says that we cannot trust our memories, and most of what we remember, especially from our early childhood, should not be trusted. Apparently, our brain adds details, and we begin to trust these inventions, and to think they are true. He might be right (annoyingly) and certainly I had one very weird experience of ‘false memory’.
It was when I had brain surgery, and therefore I guess it’s not unexpected that memory and all things brain-related would get messed up a little. But whilst I was worried that I might forget things—and even pinned up photographs of my family next to my bed, so that when I woke after the operation, I could see whether I still recognised them—I did not expect the things I did remember to be unreliable. But they were.
Soon after surgery, the consultant said I needed to have an MRI, to check nothing was wrong. I told him that I had already had a post-op MRI. He was surprised, and my husband, who had not left my side since I woke, assured the consultant that I had not. But I remembered it. I told them that I definitely had, and I had been taken by the same porter who took me for my pre-op MRI, and he had joked that this time I had to ‘travel in style’ and be wheeled in a chair instead of walking, and I felt embarrassed because I had to be wheeled across Queen’s Square with my head shaved, and people stared, and the wind was cool on my naked scalp. I remembered it all. I still do. But when the consultant went to check, it hadn’t happened. None of it. I was remembering something which was simply a thought.
The surgeon explained all this to me, and said that because I had air bubbles in my brain post-surgery, thoughts, and things I imagined, had jumped straight to the memory part of my brain, and therefore I remembered things which actually, had never happened. It’s a weird feeling, because five years on, I still remember those things.
Even in people who don’t have brain injury or surgery, memory is an unreliable thing. Our brain retains snippets of information, things noticed by our senses, and then forms a story around them. The information is stored in the hippocampus part of the brain.
Retrieving memories is another function altogether, and we tend to be able to recall things from our long term memory better than our short term one. You probably remember the name of your best friend at school, but possibly not the name of someone who you met yesterday.
Sleep is a crucial part of memory formation. When we are in deep sleep, the hippocampus replays events of the day, and the neurons—the things that store memory—which were active during those events become stimulated again. It’s a bit like the brain has a little theatre time, and re-enacts the events of the day. The neocortex (this is your ‘grey matter’) then stores these memories. If, therefore, the hippocampus goes ‘off-script’ and adds some actions of its own, these too will be stored as memory. It also means that if you don’t sleep enough—perhaps you are stressed, or ill, or have just given birth to a baby who cries all night—then your memory will be affected. Not enough sleep means the hippocampus doesn’t have time to do its little play for the neocortex, and not much information will be stored.
Memories become less reliable over time, because every time you recall something, your brain changes it slightly, and then stores the new details as memory. For example, let’s say a tea-towel was left on the hob, and caught fire. You saw this, put out the fire, threw away the tea-towel. But you did not notice the colour. While this happened, various neurons in the brain were stimulated as you saw the fire, smelt the smoke, felt the heat, etc. When you next sleep, your brain will replay this, and the neurons will be reactivated. But you cannot actually remember the colour of the tea-towel–was it blue or green?–you own both colours of towel, so your brain fills in the gap with something logical, and you store the memory as a green tea-towel. The next day, you tell someone the story of the fire, and you say, with authority, that it was the green tea-towel which caught fire. This then becomes further embedded in your memory, now you are certain that the tea-towel was green.
Now mostly, an unreliable memory is not too important, and simply means you can argue with your nearest and dearest for many hours about an event which you all remember slightly differently. But of course, in a court of law, when people are asked to be witnesses, it is hugely important. If we cannot properly trust human memory about things they have seen, how can they be asked to tell a court about what they saw several weeks or months ago? How much will those memories have changed in the intervening time? All a bit of a worry.
Thank you for reading. I hope you remember the things that are important today — and perhaps be a little less certain when people remember things differently!
If you want to read more about what it was like having a brain tumour, and how to cope after a craniotomy, you can read my book, How to Have a Brain Tumour. It’s available from Amazon, and you can read it for free if you have a Kindle.
Love, Anne x