If you’ve ever experienced a feeling of déjà vu, you’ll know just how odd the sensation can be. You’re never quite sure whether the feeling is real or whether it’s all just a trick of the mind. While there have been studies carried out on déjà vu, it’s actually a very difficult area to study as the experience is uncommon and hard to reproduce. However, it does bear several similarities to the feeling of ‘familiarity’ and as these feelings are relatively easy to reproduce under laboratory conditions, scientists are now using this kind of research to try to understand what déjà vu is and why it happens.
How scientists test feelings of familiarity
One way to test feelings of familiarity in a laboratory setting is to ask participants to quickly scan and assess the familiarity of faces or places they have seen before, together with those that they are seeing for the first time. This kind of study has enabled researchers to understand that familiarity and recollection are two separate forms of memory that are utilised together during recognition. They found that while we are able to experience the sense of familiarity quite quickly, the act of recognition will take longer. For example, if you start talking to someone whom you recognise but can’t quite place, you’ll probably start to get clues during the conversation which will trigger the memory about who they are and how you know them.
By subjecting participants to a functional MRI scan, it’s possible to see changes in activity in the area of the temporal lobe known as the perirhinal cortex when asked to distinguish familiar faces from those they have never seen before. In contrast, the parahippocampal cortex, springs into action when asked to distinguish familiar buildings from those which they are seeing for the first time.
A combination of signals is required for recollection
Based on these findings, researchers suggest that déjà vu for facial recognition may occur in the perirhinal cortex, with déjà vu for a location or place may arising from messages sent from the parahippocampal cortex. However, for the full experience of recollection to occur, a combination of signals from both areas of the brain is required, with both sets of information being sent to the hippocampus, the area of the brain that supports recollection.