Mapping the mind – Rita Carter
Memory is many different things and each different type of memory is stored and retrieved in a different way.
Memories consist of associations between a group of neurons such that when one fires they all fire, creating a specific pattern. This pattern remains encoded in the brain after the stimulation that originally gave rise to it has ceased. Memories form when a pattern is repeated frequently or in circumstances that encourage it to be encoded.
This is because each time a group of neurons fires together the tendency to do so again is increased.
Neurons fire in synchrony by setting each other off like particles in a trail of gunpowder.
Memories which are associated with personal detail or experience (‘being there’) are known as ‘episodic’ memories. These memories represent past experience, are encoded by the hippocampus and stored in the cortex – scattered around the cortical areas of the brain.
Until memories are fully encoded in the cortex they are still fragile and may quite easily be wiped out. And even when they are established they are not fixed. A memory is not, in fact, a recollection of an experience but the recollection of the last time you recalled the experience. Hence our memories are constantly changing and redeveloping.
Each time we recall something it is changed a little because it becomes mixed up with things that are happening in the present.
Reconsolidation is a process by which this slightly altered memory effectively replaces the previous one – writing over it, so to speak.
Like a pentimento.
Most sensory perceptions are not registered consciously and only a small percentage of those are retained. This leaves a tiny distillation of the past to take root in long term memory. This personal selection is distorted not only by what we choose to select but also by our unique and personal (idiosyncratic) ways of seeing things.
So, unlike the photograph, memories are not ‘pure’ recordings of what actually occurred, they are heavily edited before they are laid down.
This process of falsification continues each time a memory is recalled. As we recall things that have happened we add a bit, lose a bit, tweak a fact here, tinker with a quote there and fill in any bits that may have faded. This new version is stored back in the memory and may become difficult to distinguish from the ‘genuine’ memory.
Carter, R.(2010), Mapping the Mind, paperback edition, London, Phoenix