Where Does the Brain Store Long-Ago Memories?

By Simon Makin

When the now-famous neurological patient Henry Molaison had his brain’s hippocampus surgically sectioned to treat seizures in 1953, science’s understanding of memory inadvertently received perhaps its biggest boost ever. Molaison lost the ability to form new memories of events, and his recollection of anything that had happened during the preceding year was severely impaired. Other types of memory such as learning physical skills were unaffected, suggesting the hippocampus specifically handles the recall of events—known as “episodic” memories.

Further research on other patients with hippocampal damage confirmed recent memories are more impaired than distant ones. It appears the hippocampus provides temporary storage for new information whereas other areas may handle long-term memory. Events that we are later able to remember appear to be channeled for more permanent storage in the cortex (the outer layers of the brain responsible for higher functions such as planning and problem-solving). In the cortex these memories form gradually, becoming integrated with related information to build lasting knowledge about ourselves and the world.

Episodic memories that are intended for long-term storage accumulate to form the “autobiographical” memory that is so essential for our sense of identity. Neuroscientists know a lot about how short-term memories are formed in the brain but the processes underlying long-term storage are still not well understood.

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