How the Human Hippocampus Associates Information and Forms Episodic Memories!

Memories of real-life events or episodes are rapidly formed and require little or no repetition. Despite the importance of these memories to our daily lives, and recent advances in animal models, little is known about the neuronal mechanisms responsible for episodic memories in the human brain. Ison and Quian in Itzhak Fried's laboratory (ICLM, UCLA ) recorded the activity of hippocampal neurons in neurosurgical patients while these patients learned new associations, such as the association between American volleyball player Kerry Walsh and the Eiffel tower, as if they were meeting Ms Walsh near the Eiffel tower. These authors found that a large proportion of neurons rapidly learnt to encode these specific associations. For example, after showing a picture of Kerry Walsh next to a picture of the Eiffel Tower, hippocampal neurons initially responsive to Kerry Walsh's picture, but not to the Eifel Tower, now started to fire to the picture of the Eifel tower, as well as to the association between Kerry Walsh and the Eiffel tower (but not to other associations!). These results provide direct evidence for the neuronal mechanisms that associate complex stimuli, such as the memory of meeting a person in a particular place, a process central to the formation of episodic memories. These exciting results were recently reported in Neuron.