The Question and Answer section for Flowers for Algernon is a great resource to ask questions, find answers, and discuss the novel.
This depends where in the story you are referring to.
Charlie undergoes neurosurgery.
Strauss dealt largely with the theory and techniques of neurosurgery, describing in detail how pioneer studies on the mapping of hormone control centers enabled him to isolate and stimulate these centers while at...
Charlie is mentally challenged. He undergoes an operation to return his intelligence for a little while. This brings its own conflicts and stresses.