The great mystery of memory is how it endures. The typical neural protein only lasts for a few weeks, the cortex in a constant state of reincarnation. How, then, do our memories persist? It’s as if our remembered past can outlast the brain itself.

But wait: the mystery gets even more mysterious. A neuronal memory cannot simply be strong: it must also be specific. While each neuron has only a single nucleus, it has a teeming mass of dendritic branches. These twigs wander off in every direction, connecting to other neurons at dendritic synapses (imagine two trees whose branches touch in a dense forest). It is at these tiny crossings that our memories are made: not in the trunk of the neuronal tree, but in its sprawling canopy.

This means that every memory – represented as an altered connection between cells – cannot simply endure. It must endure in an incredibly precise way, so that the wiring diagram remains intact even as the mind gets remade, those proteins continually recycled.