Where are our memories stored

[Added May 1997]Where in the brain are our memories
stored? There is a neuron or group of neurons for each memory? You destroy
the neuron and that specific memory goes away? No. A specific memory is
almost everywhere in the brain, to destroy it you have to destroy almost
all of the brain. How we know? by experimenting with animals. But also
by looking at the parts of the brain activated during learning and
recollecting through imaging techniques.Many parts of the brain are involved
and what is amazing the parts involved are different for the same memory
during learning and retrieval.
So where are our memories in the brain?
Most likely the storage takes place as pattern of connections among
neurons
.In fact, almost every memory is made of many different patterns of neuronal connections, some for sounds, some for sights, some for smells or textures–tens of thousands of neurons firing off minute electric impulses simultaneously.

Types of memory

[Added July 1996]
Immediate memory allows the mind to hold and let go of a sensory impression within a very short time. If you look at an image and close your eyes, you’ll remember it for only about a second unless you ‘decide’ to store it.This temporary sensory is necessary to allow the brain to process for example the speech heard.

Short-term memory lasts about a minute. We use it, for instance, to retain
a phone number between reading it in the phone book and dialling.
Short-term memory can hold about seven items.

Long-term memory can last many decades.
It is estimated that the human brain could hold more then 1,000 times the
information contained in a large 20-volume encyclopaedia.

Then we have episodic memory , semantic memory and procedural memory.
You remember a ride with a horse, the meaning of the word “horse”, how to
ride a horse.

This classification can be useful to develop memorisation strategies.For example
it is easy to remember something you have done only once(episodic memory);
so why not memorising some difficult semantic information (for example meaning
of foreign words) by learning them when you visit a place never seen before, or
do in general something new.

Concerning long term memory, a more detailed discussion distinguishes between declarative memory (that includes what we called semantic and episodic memory) as things that we recall by speaking and non declarative memory or things that we recall by doing. Declarative memory is based on hippocampus and is also called explicit. Non declarative memory is based on parts of the brain different from hippocampus. Non declarative memory includes implicit i.e. memory at work when we remember how to do things. It includes also procedural memory : this is at work in priming, conditioning, etc…