Encoding of facial features by single neurons in the human amygdala and hippocampus

The human amygdala and hippocampus play a key role in face processing. However, it has been unknown how the neurons in the human amygdala and hippocampus encode facial feature information and directs eye movements to salient facial features such as the eyes and mouth. In this study, we identified a population of neurons that differentiated fixations on the eyes vs. mouth. The response of these feature-selective neurons was not dependent on fixation order, and eye-preferring and mouth-preferring neurons were not of different neuronal types. We found another population of neurons that differentiated saccades to the eyes vs. mouth. Population decoding confirmed our results and further revealed the temporal dynamics of face feature coding. Interestingly, we found that the amygdala and hippocampus played a different role in encoding face features. Lastly, we revealed two functional roles of feature-selective neurons that they encoded the salient region for face recognition and they encoded perceived social trait judgment. Together, we revealed and characterized a new class of neurons that encoded facial features. These neurons may play an important role in social perception and recognition of faces.