It happens often. We see someone who reminds us of someone else we know, or we have met, but we cannot remember where, only the face is familiar.
Whether there was a single cell in the brain responsible for familiar face recognition was a long-standing question in neuroscience. Now, it seems that those cells, which researchers called “grandmother neurons”, are a reality.
The researchers used rhesus monkeys because of their similar, but better investigated, facial processing networks. The experiment involved using functional magnetic resonance imaging (fMRI), a technique which serves to indicate regional brain activation, and showing the monkeys a set of images of both familiar and unfamiliar monkey faces. There was a twist, though: the familiar faces were of two types: personally familiar, corresponding to faces of monkeys they were acquainted with; and visually familiar, images of monkey’s faces they had seen several times.
The responses to both familiar types of faces differed quite a lot, with the general responses to personally familiar faces being much higher. But the most relevant finding was that two previously unknown regions in the temporal pole lighted up specifically when recognising familiar faces.
Actually, the change from blurred to clear familiar faces led to different responses in typical face processing areas than in the newly found “face recognition” ones. Whereas the activity increased exponentially in the first case, in the second it was more of an activity switch that went on as soon as the monkeys recognised the familiar face. In our experience, the moment when we recognise the person in front of us.
This is a first step towards understanding the neural mechanisms underlying face processing. However, the data comes only from two subjects and despite the similarities of rhesus monkeys’ brains to human brains, it would be necessary to investigate whether these areas are also located in similar regions in humans.