Types of memory
Memory is a complex and marvellous system of the brain that underpins how you learn, what you know about yourself and the world around you, even how you move.
Understanding memory is fundamental to deep questions such as: Who are we? What do we know, and how do we learn?
There are basically two types of memory: short-term or working memory; and long-term memory. Working memory engages in information in the short term, helping us to process information as it comes. Long-term memory is the storehouse of your memories of yourself and the world, and also includes procedural or skill memory, where remembered movements and actions are stored.
Working memory is an active system that's engaged while you are thinking and processing the information from the world around you. Without it, you couldn't keep in mind a number that you were about to dial, or the name of the person you'd just met.
Also called short-term memory, working memory doesn't last. As soon as you stop thinking about a phone number, or a shopping list, or become distracted, the information you were trying to keep in mind is lost.
Without the alibility to store memories you would be unable to recognise information you had encountered before, such as how to spell a word, or to recognise the faces of your nearest and dearest, so working memory also coordinates with long term memory to store information.
Your long term memory reflects your ability to learn. It includes declarative memory (facts and personal memories) and skill memory (movements and actions).
Your declarative memory is your long term knowledge about yourself and the world and holds memories that can be expressed. It is the story of your life (your episodic memory) and the things you know (semantic memory).
Episodic memory is your autobiographical story. It's a precious commodity that lets you recall your first kiss, the first time you fell in love, the first time you drove a car or rode a bike.
Your episodic memory hosts a world of information about these events. You might remember what the place looked like, what you wore, and have a sense of being there. It's the sights, sounds, feelings, and general knowledge that are part of who you are.
Episodic memory can be visual or verbal. When you meet someone you store an image of their face, as well as information attached to that — their name or occupation and how they relate to you. Episodic memory also houses our prospective memory — our ability to 'remember to remember things', such as having to buy bread after work, or meeting a friend for lunch at a particular café.
Your long term memory is also where the facts that make us such a tribe of trivia buffs are stored (semantic memory). Without our semantic memory, we'd forget that two circles close together look like eyes, or that the word 'cat' relates to a small, purring furball. We'd have trouble remembering the name of the street where we live, or the faces of the people that live there.
The gateway to your episodic memories are the hippocampi, two vaguely seahorse-shaped structures deep in the brain. At the base of the brain, closest to the spinal cord, is a structure called the cerebellum, or little brain. And it is here that your mind keeps memories of movements and actions.
Your procedural or skill memory is a primitive function that stores learnt physical activities. Its what lets us hop back on a bike after 30 years and still pedal unsteadily down the road. It keeps our movements coordinated, and lets us tackle complex movements like playing cricket, or doing an aerobics class.
Skill memories tell your brain how to move your body to dance a tango, or your fingers to type on a keyboard. Without it, we'd have to learn how to write over and over again, and still lose the information as soon as we'd finished.
Our living memory is a treasure house of knowledge and experience. It can be studied from both neurological and psychological perspectives, but it's neurology that tells us how memories are stored and retrieved by the brain.
Published 15 June 2006