How is it that we are able to remember some events in great detail whereas other memories seem to fade away over time? Our memory changes with age, so that we may have a memory slip on a trip to fetch something from the next room, but we’re still able to recall important events from history with great detail. But why?
One important aspect of memory formation and retention is the associations we build between the information we later try to remember and other details. For example, when and where the event took place, who was there, or the feelings we felt at the time. These details not only help us as clues to search our memory, but they also allow the mental time travel we all experience when we recall those detailed memories, so that it feels like we can relive an experience in our minds.
Scientists refer to this experience as recollection, and some distinguish it from familiarity, which refers to the general feeling that we have experienced something before, but are not quite able to put our finger on all of the details of the event. For example, you see someone at the supermarket or on public transport who instantly seems very familiar, but you cannot recall who they are.
The experience of familiarity is very fast – you can quickly detect that you may know the person – but recollecting the details of who they are comes a bit more slowly (hopefully before they approach you). This is an example of how the processes differ on a subjective, or what’s called a phenomenological, level.
What’s going on in the brain
Apart from the behavioural and phenomenological differences that make the familiarity versus recollection of a face seem distinct from each other, research has also indicated that different areas of the brain underlie the phenomena. The hippocampus, within the medial temporal lobes of the brain, is strongly involved in forming the associations that help to give rise to recollection, whereas the nearby perirhinal and entorhinal cortices appear to be more important for familiarity.