Question: What are memories made of in our brains?

Sam Geen answered on 26 Jun 2013:

Memories are kept in the links between neurons (nerve cells) in the brain. Exactly how memories work is complicated and poorly understood still, but Wikipedia has some information on what we know so far: http://en.wikipedia.org/wiki/Memory

(And yes, sorry, it’s got to the point where I’m just linking to Wikipedia)

EDIT: My very excellent sister emailed me to say this:
“This question is, at a first brush, a philosophical one, i.e. are qualities of mind, such as memory, purely physical and based in the brain? Or are they made of some other non-material substance? Since damaging certain areas of the brain can lead to loss of memory, the evidence is very strongly on the side of memories being material. At this point Philosophers continue bickering, but the argument is now compelling enough for us to now turn to the science!
All brain activity, and presumably therefore mind activities such as memory, arises from little charges of electricity (electrical potentials) being communicated between special cells called neurons. (You can actually ‘read’ this electricity on the skin of your scalp with the right machine!) From here it gets a lot more complicated and we’re still learning a lot, but in principle we can say that memories are the result of a large network of these cells working in unison. The memory is created and ‘stored’ by the pathways between certain cells/groups of cells being strengthened (something called long-term potentiation – science is all about the fancy words!). Think of it like paths in a field of tall grass – the first time someone walks through  the field, their feet will push some of the stalks flat making a path, this will then mean that when the next person comes along they will probably chose to follow the same route across the field as the first person because it is easier, and their passage will, again, make the path more concrete. This is why repeating facts increases their strength in memory, because each time you remember, that path through the grass becomes a little more clear until it is a well-beaten track!
Essentially then, memory is made of those paths in your brain, however, things are a little more complicated because those paths aren’t just formed anywhere, they’re found in specific parts of the brain. The most important of these is the hippocampus (hippocampus means seahorse in greek, which you can sort of understand if you squint http://en.wikipedia.org/wiki/File:Hippocampus_and_seahorse_cropped.JPG !) If the hippocampus is destroyed it’s impossible to create new autobiographical memories (these being memories about yourself and past, such as which infant school you went to and the day that your brother threw a baseball bat and it hit you on the head!), so if you lost your hippocampus you could win Gold at the Olympics or get married and not remember it the next day. Interesting fact!: I say autobiographical memory because Psychologists differentiate between these types of memory and memories which are about how to do stuff, like riding a bike or playing the guitar, which we call Procedural memory.
There is a very interesting and sad story about a poor man called Henry Molaison who had his hippocampus removed by foolish surgeons who were trying to cure his epilspy. Following the surgery he could remember his childhood but not his recent life, so even if you had met him five minutes ago, if you left the room and came back in again he would think you had never met before and he would greet his poor wife as if they hadn’t met in years, even if she had only popped out for a minute to make a cup of tea. What is even more fascinating is that even though he couldn’t remember what he’d had for breakfast in the morning, he learnt to play the piano after the surgery!”