A memory may feel abstract or immaterial, but it is actually a biochemical process taking place in the brain. It involves neurons communicating with each other via the “wires” or synapses connecting them.
The pathway an electrochemical signal follows as it continually travels from neuron to synapse to neuron constitutes a memory. Whenever you have that memory, the same pathway gets activated. And the more it’s activated, the more it becomes hardwired into the brain’s circuitry. Eventually, it becomes a long-term memory.
Activation also requires enzymes, molecules that set off chemical reactions. The problem is that these enzymes don’t exist for longer than a week. If a memory is to endure, it would seem that the enzymes would have to remain functioning for years or even decades.
Once the enzymes turn off, one would expect the memories to go with them. “This became a holy grail in neuroscience,” Lisman says. “How can a molecule in your brain serve as a memory? How does nature accomplish this?”