DEAR DOCTOR K:
How do our brains create memories? Are our memories stored in some sort of “memory bank”?
A memory is not a single entity, like a book on a shelf. It is more like a cloth that weaves together multiple facets of sensory, emotional and factual information.
Different areas of the brain process and store different aspects of a memory. For example, when you learned a song — “The Star-Spangled Banner,” say — you stored the words in a different region of your brain from where you stored the song’s melody. If you associate “The Star-Spangled Banner” with an image of the American flag, that memory might be stored in the visual processing area of the brain. Your memories are thus intricately broken down and cross-referenced. I’ve put an illustration showing the different areas of the brain and the functions they control below.
But how does the information you encounter get filed away?
Stage 1: Acquisition. When you learn new information, it first takes the form of temporary pathways of nerve cell activity in the brain. This is short-term memory.
Most of this information quickly fades. The memories that endure are those that were encoded most completely in the first place — the information that you paid the closest attention to when you learned it. Memories that involve multiple senses as well as emotions are more likely to be retained.
You probably remember clearly what you were doing when you heard about the 9/11 terrorist attacks, for example. You probably remember who else was with you, where you were, the first picture you saw of the twin towers. That’s because the emotional charge of learning that our country had been attacked caused you to store everything about that moment in your memory.
But you probably have no idea what you were doing exactly 24 hours before and 24 hours after you heard about the 9/11 attacks.
Stage 2: Consolidation. For short-term memory to become long-term memory, the initial neuronal pathways must be strengthened. When an event is emotionally charged, it is more likely to become part of long-term memory. Once a memory is established (consolidated), it is stored in areas of the cerebral cortex. That’s the large, domed outer layer of the brain.
Stage 3: Retrieval. Memories are stored in the brain as unique patterns of nerve cell activation. When you’re not thinking about a memory, the pattern is inactive. When you want to recall a memory, your brain must reactivate the pattern. How long this takes depends on how familiar you are with the information you’re looking for.
Knowledge about the different types of memory, and where in the brain they are housed, has come from research. The next frontier is learning how memories are stored. What brain chemicals are involved in receiving, consolidating and retrieving a memory? In the past 30 years, and particularly in the past 10 years, brain scientists have begun to understand that mystery.
And, fortunately, when they discover something they write it down and publish it — in case they forget it themselves.