The loss of memory, or amnesia, may be triggered by a traumatic physical or emotional event or mental disorder. It exists in two forms; anterograde amnesia prevents the formation of new memories (as depicted in the film Memento, 2000 and the regal tang fish Dory in Finding Nemo, 2003). Retrograde amnesia, from which Walser is suffering, is the loss of pre-existing memories formed before the onset of amnesia.
Traumatic amnesia - usually caused by a knock on the head - usually results in transient for getfulness, which may last as little as a few hours or throughout a person's life. It can also disrupt a person's ability to make judgements or solve problems, to control muscles or emotions and general intellectual performance.
The dramatic potential of amnesia, of a person returned to an earlier state of being, makes it a regular plot device in literature. Rebecca West's The Return of the Soldier (1918) sees a shell-shocked soldier returning from World War one with no recollection of his wife, but believing himself to be twenty years old an in love with an innkeeper's daughter. The Persistence of Memory (1998) by Gordon McAlpine introduces an amnesiac and half-drowned stranger into a community, and explores how he and they create a self for him. In reality, there have been several cases of individuals discovered wandering and of international searches for their true, forgotten identities. In 2005 the 'Piano Man' was found in England; he did not speak, but played the piano non-stop for four hours. He was later identified as Andreas Grassl from Germany.
Walser's amnesia supports the concept of Limbo introduced earlier in the novel; as Fevvers and the others disappear into the physical wilderness, he is lost in his own mental wilderness in preparation to 'hatch out' in readiness for the twentieth century. The first thing which he identifies is an egg, reminding the reader of many earlier references to him as unfinished, young, and unhatched. In his simple state he is charmed by natural beauty, fascinated by simplicity, losing some of his journalistic cynicism and living in childlike acceptance of all that he meets without questioning its probability.