The role of the hippocampus in learning and memory has been studied for many decades particularly since the late 1950s, following the results of surgery, in an American male, to remove most of the hippocampus.[32] It remains unclear how the hippocampus enables new memory formation, but one process, called long term potentiation (LTP), occurs in this brain region.[2] LTP involves long-lasting strengthening of synaptic connections after repeated stimulation.[3] While the dentate gyrus shows LTP, it is also one of the few regions of the mammalian brain where adult neurogenesis (the formation of new neurons) takes place.