Wrinkle Maps, how does it work? how do we make them?

hey guys, question about wrinkle maps. i know when we video game model a character's face, the character will have different kinds of facial expression, for example a shouting face and a neutral face. i know in terms of modeling the character in high-poly, we will just do it in ZBrush and make different layers for different face expressions. but i dont understand how do we keep the topology similar though. because a shouting face and a sleeping face will look significantly different. and i heard people say that they will make many wrinkle maps and but it onto a model and that depending on how we move the face into different expression, the program (maybe a game engine or maya?) will read the movement and load the most relevant wrinkle map onto the model. is that how it works? and what program do people use to show this kinds of thing? Maya? Unreal? or an engine made in-house by a video game developer? so basically, my really big question is how do we make two face meshes of the same character, with similar topology, similar rigged skin painting, but will be used simultaneously because it belonged to the same character, and how does said engine know what wrinkle map to use? and what about the part between a shouting face and a neutral face? use 50% opacity of one wrinkle map and use 50% of another? i need someone to explain this to me, i cant find any information about this on google or anywhere. or link me a tutorial or w/e. thanks for reading guy!