Human hippocampal neurons predict how well word pairs will be remembered

What is the neuronal basis for whether an experience is recalled or forgott en? In contrast to recognition, recall is difficult to study in nonhuman pr imates and rarely is accessible at the single neuron level in humans. We re corded 128 medial temporal lobe (MTL) neurons in patients implanted with in tracranial microelectrodes while they encoded and recalled word paired asso ciates. Neurons in the amygdala, entorhinal cortex, and hippocampus showed altered activity during encoding (9%), recall (22%), and both task phases ( 23%). The responses of hippocampal neurons during encoding predicted whethe r or not subjects later remembered the pairs successfully. Entorhinal corte x neuronal activity during retrieval was correlated with recall success, Th ese data provide support at the single neuron level for MTL contributions t o encoding and retrieval, white also suggesting there may be differences in the revel of contribution of MTL regions to these memory processes.