1. Registration: The type of information you’re receiving determines which region of your brain is active. For example, words are initially processed in the language regions of the brain, pictures initially in the visual regions. This is where your memories are “registered.”
2. Immediate memory: When information comes into a region, it comes in as a pattern of nerve cell activity. This nerve cell activity normally persists for just a short period of time – seconds or less. This is of course what we deem “Immediate” memory
3. Permanent (long-term) memory: If the information in this temporary pattern of activity is to be permanently stored (and most is not) it will be saved within the same regions of the brain. Saving the patterns of activity consists of changing nerve cell connections so that the pattern of activity can be called forth again, at some later time. To do this, some nerve cell connections are strengthened, while others may be weakened. These changes are relatively permanent, although the changes may take weeks or months to completely solidify.
Even though the solidification occurs in the regions of the brain that contained the original activity, the signal to make the solidification occur came from other regions. The best known of these regions with such signaling functions are the hippocampus and the thalamus. The hippocampus is on the inner side of the temporal lobe; the thalamus is located deep within the center of the brain.
4. Memory access: Remembering what you’ve learned may be a simple matter of just reactivating a latent memory – for example, by seeing a picture again and recognizing it as familiar. In this case, the memories get reactivated in the region of the brain where they were first stored. The measurement of familiarity – the sense of how familiar something is, or how recently you learned it – seems to be done in parts of the temporal lobe, particularly in or near a structure called the amygdala, which sits just in front of the hippocampus.
This simple memory retrieval operates very quickly. You can decide that a picture is familiar to you or not in less than one-half a second, measuring from the very start of the time you see the picture to the start of when you say “yes” or “no.”
Once the picture has been registered in your brain (which takes about two-tenths of a second), it takes you about two-tenths of a second to actually make the decision, and about another two-tenths of a second to say your answer. The total time it actually takes you is a little less than the time you spend on each stage, because some of these stages can overlap. You start deciding a picture is familiar or not while the image of the picture is still developing within your mind.