EARLY on July 2, 2003, a 35-year-old Englishman woke up on the outer reaches of the New York subway system.

The scenery, dreary housing projects and run-down urban sprawl, was unfamiliar to him. It occurred to him that he didn’t know where he was going. Then, with a fear that grew more acute with every second, he realised that he also had no recollection of where he had come from, and no idea who he was.

Doug Bruce, a successful, social, confident individual, had been struck by a rare form of amnesia that had wiped all memories of his gilded life.

The case is the subject of Unknown White Male, a fascinating and thoughtful documentary that attempts to piece together what happened to him and follows Bruce as he reassembles a life for himself.

Rupert Murray, the film-maker and a long-time friend of the pre-amnesiac Bruce, also examines the reactions of friends and loved-ones who have to come to terms with the seismic shifts in their relationships with Doug, as 15 years of easy banter are replaced with strained pleasantries with a stranger.

More fundamental questions are raised by the film: how much of personality is determined by past experience? How much of who we are is genetically predisposed and independent of the memories we form along the way? Bruce’s case would seem to support the nurture argument rather than nature. Post-accident Doug is a very different person — more reflective, serious, emotionally open and articulate, Doug has, you suspect, unconsciously absorbed some traits of the women who nurtured him in the immediate aftermath. His articulacy is curious and by no means complete. While his vocabulary permits him to expand on his emotional reaction to seeing the ocean for the first time, he no longer has any idea what “Chelsea Football Club” means.

None of the old friends from his twenties and early thirties is blunt enough to say it, but humour is a casualty of Bruce’s condition. Without the shared frame of comedy reference, the comic shorthand developed over the years is redundant. They mourn the in-jokes as much as the intimacy. Male friends reminisce about the old Doug’s cynicism — a trait that belongs to the worldly wise, to those hard-wired to pick up on clichés.

The new Doug is seeing the world with the eyes of a newborn but the mind of an adult. Since everything is fresh, he’s yet to learn the jaded ennui of his previous self. He is acutely aware of the unique opportunity that has been afforded him. Everyday encounters are nerve-jangling, intense experiences — it’s as if, one expert says, Doug’s senses have been sharpened.

Perhaps understandably, he is ambivalent about whether he even wants his memory back, bringing with it the ghost of an older self that you sense Doug now views with a certain amount of trepidation.

This is an extraordinary film that poses some universal and profound questions about ourselves and what exactly made us who we are.