In this video Quinn Cunningham discusses (in VERY much layman’s terms) Muscle Memory as it relates to firearms training. Developing muscle memory is process called myelination that occurs in the brain. This is a process of developing the myelin sheath over the neural pathways causing greater conductivity.
Quinn is not a psychologist, but he did stay at a Holiday Inn last night. If you would like to develop a greater understanding of the process, go to https://en.wikipedia.org/wiki/Myelin