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The Brain : Learning and Memory
CHAPTER 1. MEMORIES ARE MADE OF THIS Amemory of the coffee you had with a friend last week, for example, could include the taste and smell of the coffee, the café’s interior design, the sound of an ambulance’s siren as it drove past, and the topics of conversation you discussed. These components of your experience would have activated various parts of your neocortex. But the episode itself would initially be stored in the hippocampus. Over time this memory is consolidated, with its long- term storage thought to be distributed in different parts of the neocortex. Once A memory has been stored, how is it accessed? According to one popular theory, the hippocampus is critical, serving as a memory index. To use an analogy: when functioning well, memory is like HOW MEMORIES ARE ACCESSED YOUR EXPERIENCES IN THE WORLD ARE BASED ON INFORMATION RECEIVED THROUGH A COMBINATION OF SENSES: SIGHT, TOUCH, HEARING, TASTE AND SMELL. a digital database or an old-school- style office filing cabinet: something triggers a search of the database, and we retrieve and recall the memory. Returning to our café story, when your friend mentions how much she liked the café’s stylish interior, you picture the inside of the café, making your visual cortex – the part of the brain that receives and processes sensory nerve impulses from the eyes – become active in a similar pattern to when you saw the café first- hand. Because of synaptic plasticity and strengthened connections (see previous page), this visual seed is enough to access the ‘café with friend’ scene in the hippocampus’s index. To actually recall the memory, the hippocampus then directs neuronal traffic back to the appropriate circuits of the neocortex, reactivating the sound of the ambulance siren, the taste of the coffee, the topics of conversation and any other components of the ‘café with friend’ memory. This idea of memory indexing and recollection is still only a theory.