SINGLE NEURON ACTIVITY IN HUMAN HIPPOCAMPUS AND AMYGDALA DURING RECOGNITION OF FACES AND OBJECTS

The hippocampus and its associated structures play a key role in human memory, yet the underlying neuronal mechanisms remain unknown. Here, we report that during encoding and recognition, single neurons in the medial temporal lobe discriminated faces from inanimate objects. Some units responded selectively to specific emotional expressions or to co njunctions of facial expression and gender. Such units were especially prevalent during recognition, and the responses depended on stimulus novelty or familiarity. Traces of exposure to faces or objects were fo und a few seconds after stimulus removal as well as 10 hr later. Some neurons maintained a record of previous stimulus presentation that was more accurate than the person's conscious recollection. We propose th at the human medial temporal lobe constructs a ''cognitive map'' of st imulus attributes comparable to the map of the spatial environment des cribed in the rodent hippocampus.