This is an answer I wrote to a Quora question in October 2023
Despite this unfortunately widespread myth, it’s not true that all cells in the body are replaced within seven years. Your brain, for example, does not produce any new neurons from the moment you’re born. Hence, the cells in the brain cannot be “replaced” within seven years.
Some previous answers have wrongly stated that memories are created through the formation of proteins. This is misleading, as it implies that the memory is recorded within the protein structure, which is completely false.
Memories are encoded by connections of specific neurons.
The brain is an interconnection of neurons. Each one of them can be connected to one or more different neurons.
Let’s imagine that you have a brain containing 100 neurons and that each neuron is numbered 1 to 100.
The memory of the taste of chocolate is encoded through the connection between neurons 1, 15, and 72.
And the memory of your favourite song is encoded as the connection between neurons 23, 42, 66, and 81.
Whenever you remember what chocolate tastes like, what your brain is doing is “firing” neurons 1, 15, and 72 together. And you remember your favourite song it fires neurons 23, 42, 66, and 81 together.
People that have Alzheimers for example forget things because their neurons are dying. They’re losing the connections. In our examples above, if the person lost Neuron number 15, they would no longer be able to remember the taste of chocolate.
This is an overly simplified explanation of memories, but it gets the gist of it.
I lied to you.
When I said earlier that the cells in the brain do not get replaced, I was partially lying to you.
Determining if a cell gets replaced or not depends on how you define “replaced”. If by “replaced” you mean a complete turnover of all the molecules that make up the cell without destroying the cell, then yes. No cell in your body is made of the same atoms as they were 7 years ago.
What I’m describing here is equivalent to saying that I’d replace every brick that makes the Empire State Building, one at a time, without ever destroying the building. Would it be a different building? Technically yes, but it would still be the Empire State Building.
The reason why you’re able to remember things even if every atom of your cells is replaced after a certain period of time (which may or may not be 7 years), is because the structure of the cells remains the same! The connections between the brain cells are still identical. Hence, the memories remain.
I hope this was informative!
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