Memory: I can't remember

Memory is essential for survival. The brain stores all kinds of memories, like the way to ride a bike, what happened yesterday and even the meaning of the word 'memory'. But memories are fragile and when the brain is damaged by an accident or an illness, memories can disappear along with the ability to remember. Could you survive without your memory? Find out how Sarah, an amnesic, copes with her loss and how her brain used to store memory.  

By: Dr Jenny Gimpel (Guest) , Dr Hugo Spiers (University College, University of London)

  • Duration 10 mins
  • Updated Friday 16th June 2006
  • Introductory level
  • Posted under Psychology
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I can't remember where I am. I haven't been asleep but it feels like I’m waking from a dream. I’m bleeding, I wonder why? Images of a handbag – a blue one like the kind my mother used to wear - are flashing in my mind, but I’m not sure if the woman on the bus seat next to me really did swing her bag at me. Why would she do that?

I’m standing at a bus stop and I remember ringing the bell for this stop, so I must be in the right place. I think I recognise the shop across the road – it looks like the corner shop I used to work in when I was fifteen - but I can’t remember why I travelled here…

My name is Sarah. The doctors tell me I have a classic case of amnesia. My childhood memories have stayed with me, but I can’t remember whether I’ve eaten breakfast or lunch today.

The scientists find me fascinating. I sit in their testing rooms trying to memorise a phone number or a list of words, but it seems that after a few minutes I’ve forgotten, although sometimes I’m able to guess them correctly. My short-term memory works but I can’t keep hold of memories of new events or facts for very long. That’s why I’m standing at this bus stop wondering why I came here today. Is it someone’s birthday party? Do I have a doctor’s appointment?

At least I can remember how to read. My old semantic memories – knowledge of objects, words and their meanings that I learnt while growing up - will help me study this bus map, read the information and try to make some sense of where I am. Bother! The names of nearby places mean nothing to me, so I head for something called a golf course up the road.

I can see people swinging metal sticks at little white balls. It looks very difficult. Let me try with this branch lying in the gutter. I pick up the branch and flick a discarded coffee cup up in the air. Yes! It lands squarely where I’ve aimed it, in the middle of a car roof up the road. So I can play this game called golf, though I can’t remember having any lessons or learning the rules.

This must be something I learnt to do after my accident, so my procedural memory – my ability to learn actions – is still intact. But my semantic memory has evidently been damaged by the blow to my head, which is why the word golf seems so alien to me.

The scientists tell me that a part of my brain shaped like a sea-horse – the hippocampus – is no longer working properly, which is why I can’t remember important things like whether my mother is still alive.

Maybe I should return to the bus stop in case someone is meeting me there. I retrace my steps while rummaging through my handbag. I find a note saying “Bus stop, 3.30pm”. It’s 3.25pm. Good. I also discover a collection of articles on memory and start reading them to pass the time.

The first article is about the hippocampus, how it encodes people’s experiences as they pass through life. My brain still has a record of the time I ate a rotten watermelon while sunbathing on the beach, and spent a punishing night throwing up. I treasure the old memories of my mother holding my head over the toilet bowl, stroking my brow while I retched. I must have been eight or nine. But if you asked me where my mother lives today, I couldn’t tell you. Post-accident events can’t be stored in my brain. The older ones, from my childhood, must have crept out of my hippocampus before the accident.

I can't remember what happened in the accident or even a few years beforehand. These memories seem to have been knocked out. This, they say, is called retrograde amnesia – the loss of memories for events or facts that I learnt before the onset of my amnesia. Sometimes the loss can extend right back to childhood; thankfully in my case it’s only a few years. Most amnesics lose their memories for personally experienced events, and some can't remember factual information from before the accident, like their home address or what an old friend's name is.

The article says that another part of the brain, the amygdala, controls emotional memory. Maybe that’s what makes me feel scared whenever I walk barefoot on sand. Why do I react that way? I must have had quite a few bad experiences on sandy beaches. I think it’s called conditioning – my amygdala has linked sand with unpleasant events. I guess it’s a survival mechanism, to help me learn to avoid dangerous objects or places, but it’s annoying that I can’t enjoy the feel of sand on my bare feet.

I’ve found another article in my bag on a type of memory called priming. Hey! My name is mentioned. I must have been tested in one of the experiments. It says here that I’ve retained my unconscious ability to increase the speed with which I respond to things I’ve seen or heard recently. Although I don’t remember them showing me an animal and then showing it to me again the next day, the second time I see the animal I respond more quickly to it, though it feels like I’m seeing it for the first time. Well, that’s what it says in the article. I don’t remember any of this.

Some people are worse off than me. People with Korsakoff's amnesia are compelled to tell lies, to make things up about their past. Nobody understands why they do this. Maybe they’re desperate to fill in the blanks. Or maybe they've lost the ability to judge their own memories.

There’s something here about someone with semantic dementia. Poor bloke, he keeps pouring bleach into his cups of tea, because he doesn’t know it’s not milk. His semantic dementia means he fails to remember knowledge about objects, words and people. Though, unlike me, he can still remember day to day events well. This is because the disease affects parts of the temporal and frontal lobes of his brain but not so badly his hippocampus.

Some people lose their ability to remember words while still being able to recognise faces and other objects. For others it’s the reverse. It says here that the right side of the brain is involved in non-verbal memory while the left side does more with verbal memory. For me, I've lost a bit of both.

Here’s a third article, about how memory can be fragile even in the healthiest of people. How reliable are witness statements? Not very reliable, according to the article. “A woman witnesses an accident involving a blue car hitting a signpost at a junction. Later, she is asked which way the red car approached the accident spot. She replies, from the left fork in the road. If she is then asked what colour the car was, she may well answer red rather than blue. Her memory is distorted by first question’s suggestion that the car was red.”

There’s another interesting bit further down the page. “The good news is that memory can be improved using simple tricks. Associating an unfamiliar object with a well-known place can help you retrieve the memory of the object more quickly by first imagining the place. This is known as the Method of Loci and is a common trick used by memory experts.”

“If you study for exams with music in the background, you may do better in your exams if you can listen to music while taking them. It’s easier to remember things if you place yourself in an environment where you earlier made use of them. So next time you lose your glasses, go back to the place you last remember seeing them. It will help jog your memory of what you subsequently did with them.” Good tip, but how useful is it to me?

The article waffles on about brain imaging, using something called functional magnetic resonance imaging to measure the blood as it moves through the brain. “Blood continuously flows around the brain supplying oxygen and nutrients to billions of nerve cells, making the head one of the hottest regions of the body. If, for example, you are trying to remember a shopping list, cells in your prefrontal cortex will be sending more messages to neighbouring cells and brain regions. As they send the messages they ‘call out’ for more oxygen, so the blood rushes to the cells to supply them with oxygen. MRI measures the changes in oxygen in the blood.”

Blimey! It says here that scientists have built artificial brains called neural networks that can learn independently. They’re actually mathematical models of layers of brain cells connected together in different ways. Apparently these cells can rearrange their connections to store information in the network. Like in Terminator II, when Arnold Schwarzenegger rearranges the connections in his neural network processor to learn the right and wrong way to say “hasta la vista, baby”. But if too many memories are laid down over too many cells in the network, it overloads and goes from remembering lots of things to none at all – otherwise known as catastrophic forgetting.

Speaking of forgetting, what am I doing still standing at this bus stop? I’m hungry and my feet are sore. I hope someone comes soon, because I won’t be able to find my own way home. The hippocampus is supposed to help me navigate by storing a mental map of the world, but my map seems to have disintegrated since the accident. Wait – is that woman across the road waving at me? She seems to know me. She walks towards me. Perhaps I can borrow her mental map to find my way home…

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