Learning, memory, and the retrieval of memory seem to be separate phenomena, controlled by separate areas of the brain. Ample evidence shows that the hippocampus is involved in learning. For example, intense electrical activity occurs in the hippocampus during learning. Even more striking are the results of hippocampal damage. A person whose hippocampus is destroyed retains most of his or her memories but is unable to learn anything that occurs after the loss. One victim was unable to recall his address or find his way home after 6 years at the same residence. He could be entertained indefinitely by reading the same magazine over and over, and people whom he saw regularly required reintroduction at each encounter. People with extensive hippocampal damage can recall events momentarily, bit the memory rapidly fades, as does the memory of a dream upon awakening. This phenomenon has led to the hypothesis that the hippocampus is responsible for transferring information from working into long-term memory.

Retrieval, or recall, of established long-term memories is localized in another area of the brain, the outer temporal lobes of the cerebral hemispheres. In a famous series of experiments in the 1940s, neurosurgeon Wilder Penfield electrically stimulated the temporal lobes of conscious patients undergoing brain surgery. The patients did not merely recall memories but felt that they were experiencing past events right there in the operating room!The site of storage of complex long-term memories is much less clear. The psychologist Karl Lashley spent many years training rats and subsequently damaging parts of their brains in an effort to locate the site of the memory, but failed. None of the injuries could erase a memory completely. In 1950, a frustrated Lashley wrote:" I sometimes feel, in reviewing the evidence on the localization of the memory trace, that the necessary conclusion is that learning just is not possible."

Some researchers suggest that each memory is stored in numerous distinct places in the brain. Or perhaps memories are stored like a hologram image, both everywhere and nowhere at the same time: the memory is more precise if the whole brain is intact, but each "bit" of cerebral hemisphere can store an essentially complete memory. Further research might provide definitive answers, but for now, the storage site of memories remains an unsolved mystery.