Concept cells in the human medial temporal lobe (MTL) respond selectively to pictures of specific individuals and places. In this talk I will discuss two issues. First, I will show how the identification and characterization of different MTL neuron types recorded in vivo give us some clues on the underlying mechanisms leading to high stimulus selectivity. Second, I will show that some of these concept cells participate in memory circuits. For this, I will present results on a recent experiment in which we recorded the activity of MTL neurons in neurosurgical patients while they learned new associations. Pairs of unrelated pictures, one of a person and another of a place, were used to construct a meaningful association modeling the episodic memory of meeting a person in a particular place. We found that a large proportion of responsive neurons expanded their selectivity to encode these specific associations within a few trials and even after one trial: cells initially responsive to one picture started firing to the associated one but not to others. Our results provide a key neural substrate for the rapid inception of associations that is crucial for the formation of episodic memories.