Eyes, nose, mouth, ears, cheeks, hair ... our eyes can easily capture the image of another person’s facial structure and recognize it instantaneously. Almost formulaically, we recognize others’ facial structure patterns. Often, we can identify individuals by just a specific distinct facial region, especially by identifying features such as the eyes. This evolved ability has greatly shaped human life as highly social beings (1). But is there a specific neuron to encode for each face that we have come to know throughout our lives?
Until now, the idea of such a neuron was just a myth. Facial recognition was thought to be a complex process involving multiple types of sensory and memory neurons in a neural circuit across diverse areas of the brain (2). A discrete cell type for a recognized person was searched for over many years. The “myth” was given the moniker “grandmother neuron” by the ideology that a single neuron would activate in response to the sight of your grandmother’s face (3). For a single neuron to relate to a familiar person, it must encompass a specific but multifaceted entity.
Recent groundbreaking research published in July 2021 in Science Magazine shows that a group of cells in the temporal pole (TP) of the brain can capture such an ability (4). While it may not exactly fit the ideal one-to-one notion of a singular grandmother neuron firing at the sight of a person, it is the closest that we’ve come to it, with a population of cells in one brain area corresponding to a familiar face. Nonetheless, it is the first finding of a hybrid brain cell. “It’s a ‘grandmother face area’ of the brain,” says Freiwald, one of the study’s researchers (5).
This recognition ability of the hybrid TP cells combines long-term memory as well as sensory information such as sight and other perceptions, like the sound of another’s voice and how they laughed (4). The location of these double-agent TP cells in the temporal lobe is crucial to its function: after all, the temporal lobe’s function includes long-term memory storage (6). Furthermore, in the developing brain, vision – processed in the occipital lobe – matures rapidly in newborns and infants (7). Hearing is fully developed in newborns because, surprise, surprise: the auditory complex is part of the temporal lobe (8). The location of the temporal and occipital lobes in the back of the brain allows for an integrated relationship between these two lobes that starts from infancy (9). This established integration indicates an intricate tie between memory and sensory information. Brain development occurs from back to front, thus confirming the importance of long-term memory and key sensory inputs such as vision and audio, which together creates recognition (10).
The discovery was innovative in its recording of electrophysiological data, thus displaying the circuitry of the brain (4). First, brain regions were identified using whole brain fMRI (functional magnetic resonance imaging) technology to get a clear visual of stimulated brain areas. The fMRI created a brain map directing researchers to the locations of the very responsive TP and AM (anterior-medial face area) so they could introduce electrodes to those regions (4). The electrodes were used to record neural signals in the form of waves, and as a result, visual, auditory, motor and somatosensory responsiveness was observed.
Surprisingly, it was found that the TP cell population responded more than three times as much to familiar faces as opposed to unfamiliar ones (4). Despite seeing all images beforehand, even the images of unfamiliar faces, it proves that passively seeing a face cannot compare to real life in person interactions, showing the value of true human connections within the psyche (4).
What this finding represents, is hope for people suffering from prosopagnosia, or face blindness (5). In the same way that it is hard for humans to distinguish animal faces of the same species, there are people who struggle with differing human faces. Around 1% of the population suffers from this debilitating and depressing condition where, in the worst case, they cannot even recognize close relatives (5). By shining a limelight on how facial recognition occurs, we can get closer to a solution for those with such a cruel condition.