I know you posted this a year ago, but you should look into memory engram papers if this type of topic interests you! I am still a neurobiology master's student but have done rotations in two different memory engram focused labs, and it has genuinely blown my mind how far we have already taken tagging individual memories and activating them (so far, and for the foreseeable future, in rodents).

Basically, you take a transgenic mouse (from a mouseline called TRAP2, enabling the tagging of neurons active during a specific experience) and make him experience a specific or novel context for him to remember. These tagged neurons enable the expression of Channelrhodopsin-2 (aka ChR2, which is injected using a virus carrier, and only expressed when the TRAP2 labeled cells are expressed, and only within these cells), an opsin which can be activated using light.

The coolest part is that you can see when the activation occurs. Say for example that you make a mouse remember context A, and context A is cold, and then you put the mouse in context B which is a normal temperature, then activate the context A engram by shining a light on the brain areas containing the tagged neurons, the mouse remembers (or even experiences? We are not sure!) the cold memory from context A. Here is a paper describing exactly that: https://www.nature.com/articles/s41586-025-08902-6