For example, in this article on wikipedia.org you can read about Kim Pik - the prototype of Dustin Hoffman's character "Rain Man". Let me highlight what is important in my opinion: Kim Peek was born with a brain that lacks the corpus callosum (it connects the right and left hemispheres of the brain) - according to scientists, brain neurons in the absence of the corpus callosum created new connections, which led to a manifold increase in memory capacity.
Neurobiology and neuropsychology are already pretty good at explaining the phenomenon of savants. This phenomenon is not associated with reserves, but with physiological characteristics in the structure of the brain of individual people, in which some functions can be more developed to the detriment of others.
You can read, for example, the books "Ungifted: Intelligence Redefined "and" Wired to Create: Unraveling the Mysteries of the Creative Mind "by Scott Barry Kaufman. If I understand correctly, these books have not been translated into Russian, and I cannot name others right away.