The reason people exist at all is because of two important things, memory and language, which have been vital in the evolution of humanity. As an example, our ancestors needed language to explain how to light a fire to keep their caves warm, and a memory to remember how to do it. So we have a memory because if we didn't we would never have evolved far enough for you to ask this question in the first place!

So, how does it work? Well the processes involved in human memory are very complex. People sometimes compare the human brain to a computer, and memory to floppy discs, but this is a bit misleading. Despite big advances in recent years memory is still a bit of mystery, and there are disagreements among the experts about exactly what is going on.

Memory is seen as a function of the brain and is defined as the ability to store and retrieve information. But there is no particular bit of the brain which is thought to be where data is stored. Many people think that there are different types of memory, after all there are lots of different types of input, so we get visual memory, auditory memory, olfactory memory, gustatoryand tactile memory. And we tend not to remember things as single, simple bits, but in a more complex way.

So you may remember the first time you had, say, a very hot chili con carne, but not just that simple fact, you'd find you'd remember it as part of a more complex set of things. So you'd probably remember that the first time you had chili was at a friend's birthday party, when you wore green jeans. So memory is very complex, and it doesn't seem to belong in any one part of the brain.

But you couldn't possibly store all this complex information in your brain, there would just be too much of it. Instead it seems like your brain takes lots of information into your short term memory, but then picks the most important information out of that to go into long term memory. You can't hold information in short term memory for very long, that's why it's called short term memory and you can't hold very much either. So it's easy to remember an 8 digit phone number, but any more than 12 is very difficult, Interestingly short term memory can be disrupted by a blow to the head or an electric shock. This rather suggests that short term memory operates by circulating nerve impulses which can be disrupted very easily. But nobody is quite sure how long term memory works. Because we can remember so much information some scientists think that it must be stored using very small things, perhaps a protein molecule. But there are doubts about this, especially as protein molecules live for much less time than our long term memory lasts. Some think that memories are stored by changing the ways brain cells link together, but it is difficult to study this in the laboratory.

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