You don’t need to remember everything you are exposed to, so your brain sorts what is necessary and turns that into memories, dumping the rest. Just like Jason Bourne in the movie ‘The Bourne Identity’, you can train your brain to notice and remember more. New information and experiences are better remembered if they can be associated with things we already know.
There are three main stages of memory formation: sensory memory; short term memory and long term memory. Some people argue that these are arbitrary divisions, but at each stage information is sorted into necessary (to be stored) and unnecessary (to be discarded).
The first stage is the formation of sensory memory. Your five senses: touch; sight; hearing; smell and taste are constantly receiving input from the environment. The brain sorts this input and automatically stores the perceptions that might be needed later. This is done unconsciously and stored automatically, but only for 200-500 milliseconds.
Then sensory memory is encoded into short term memory. Encoding is basically changes in the shape of neurons and the signals sent between neurons.Short term memories last 20-30 seconds, and will disappear completely if no conscious effort is made to keep these memories. Saying things out loud, repeating them or associating them with things you already know will make them easier to remember and more likely to be turned into long term memories. People have been using tricks like memory rings for centuries to keep short term memories. Most people can hold five to nine items in their short term memory. You can cheat a little bit with this by separating information into chunks like a phone number 111-222-3333. Each chunk is then remembered as a single item.
New information pushes out older information in short term memory. We are constantly receiving information from our environment which is decoded by the sensory cortex in the brain. So the only way to stop something slipping out of our short term memory is to pay attention to it. The brain then recalls information likely to go with the new items in the short term memory. Some scientists think that all memories pass from short to long term memory. But some might be harder than others to recall. Newer theories propose that some sorting occurs and only more important memories are stored long term. The hippocampus is the part of the brain that integrates new short term memories with stored memories and works out which should be consolidated into long term memories to be stored.
Consolidation from short to long term memories occurs via long term potentiation. Long term potentiation occurs when connections between neurons are formed and strengthened. These form into neural circuits that fire whenever the memory is recalled. These are stable changes in neural circuits unlike the transient changes that occur in short term memory. Scientists recently proved that this mechanism exists by creating false memories in rats. Repeatedly thinking about something or remembering something will strengthen these circuits and thus strengthen the memory. Long term memory is processed in the hippocampus. The hippocampus actually shrinks in Alzheimer’s patients.
The opposite of long term potentiation is long term deterioration which is weakening of synapses (the connections between neurons). This is thought to be how we forget things. Although some scientists believe that we never really forget anything, some things just become very difficult to dredge up out of the depths of our brains.
Here’s a cool video on memory formation.