Who is Jimmie G. from The Man Who Mistook His Wife for a Hat and Other Clinical Tales and what is their importance?

Jimmie G. is a man in his mid-forties when Dr. Sacks first meets him. Time stands still for Jimmie and he has no recollection of events that have happened since 1945. The condition seems to frustrate Dr. Sacks and his medical staff more than Jimmie. Jimmie maintains a sense of humor when confronted with things that took place after 1945 and is still able to recognize his brother, even though he marvels at the way his brother has aged so quickly.