Neurologist and author Oliver Sacks tells his great-niece Eugenie Samuels why in his latest book he felt compelled to revisit his childhood.

Eugenie Samuels : Uncle Tungsten is the first one of your books where you talk about the family.

Oliver Sacks : The Uncle Tungsten of the book title is Uncle Dave, who pioneered the manufacture of the tungsten light bulb in Britain. He spent many hours showing me round his factory and talking to me about chemistry. Uncle Dave lost his eldest son to a tumour. I wonder whether the loss of this very bright son, who would have followed him into the business, made a place for me. I'm reading The Education of Henry Adams . It made me think that Uncle Tungsten is, in some ways, the Education of Oliver Sacks.

ES : Very little of the book talks about school. It's more about the family.

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OS : Henry Adams says: "The family was rather an atmosphere than an influence." He goes on: "Dislike of school was so strong as to be a positive gain." I don't want to be too negative about school. There was one schoolmaster I liked very much. But my main gratitude is to books, to museums, to my uncles and to my parents for allowing me free rein to run my chemistry experiments in the house.

ES : You were bullied and beaten at the Midlands boarding school you were sent to when you and your brother Michael were evacuated during the war, but your parents' first priority, as doctors, was to their patients. I remember your mother - my great grandmother - in particular seemed distant and cold. Perhaps they didn't know how to help you. Was that why they tolerated the whizz-bangs and smells in the house when you discovered science? Did they understand that science was your therapy? Do you think it would have helped if they had talked to you directly about being so unhappy?

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OS : It might have. I couldn't speak out. This was partly my own shyness. But partly, they didn't open the way. I am reminded of the episode where Ma (one of the first female obstetricians in London) brought back a stillborn baby from her work and had me help her dissect it. One editor thought I shouldn't have put this in the book, and my brother Marcus was uncomfortable with it too. The point is maybe, although there was nothing malicious in Ma, her interest swept her along and she would forget that I was just a little boy. My other hesitation was whether I should have spoken of Michael's psychosis.

ES : This is the first time you have spoken publicly about having a brother with schizophrenia. I suppose you felt it wasn't relevant to your writing?

OS : Whereas here it is. Whatever disposition to mental illness Michael has, the terrible beatings at our school undoubtedly pushed him overboard. My own reaction was to just try as hard as I could to hold together myself.

ES : You write that your parents removed you from the school "just in time", even though they didn't know what was going on. In time for what?

OS : I think I was getting a bit nutty. I don't know how strong the congenital dispositions to schizophrenia are. I know Michael was already fearful and anxious when he was eight or nine. I think I was relatively robust myself before the war, but I came back from evacuation in a very fearful state. As I moved through the teens, it perhaps became clear that I would merely be severely neurotic, but not psychotic.

ES : The reactions to sensations and colours in your writing are very intense. Is that just you being descriptive as a writer or is there a hint of psychosis there?

OS : No, I think ordinary perceptions can be very vivid. And so can conceptions. I'm not really an abstract thinker. To me, it's a sensual world.

ES : As a child you seem to have been more grounded in the abstract. The periodic table obsessed you, and you enjoyed numbers and number theory. As an adult studying the mind, have you ever craved a sort of neurological table to categorise your findings?

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OS : Biological systems are too complex. After I wrote Awakenings , Aleksandr Luria (who pioneered the treatment of Parkinson's disease with the molecule L-dopa) asked me why no two patients reacted to L-dopa in the same way. I don't know, but we know that all atoms of tungsten are the same.

ES : What kind of a world was it for Michael?

OS : I was probably closest to Michael in the years that followed the late 1940s and 1950s. By then he'd had a number of episodes. He would say that during a psychosis, the meaning of everything would become questionable. He would portray the psychoses as crises while he was trying to reorganise his inner world. He knew he needed medication so that he couldn't harm himself or others, but he wished his mind could be free, albeit within a cocoon of physical protection. I'm not sure that Michael was wrong because there is some suggestion that adolescent schizophrenia can find its own resolution.

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ES : Aren't these insights common in people who are mentally ill?

OS : I think some sorts of existential crises are very real, but it may be that a malignant, organic process can present as acute existential questions. Temporal lobe epilepsy will often present as mystical awe. I find it an unresolved question. It does mean I'm not entirely happy with a blanket term like mental illness. On the other hand, I wouldn't go so far as to say mental illness is purely a sort of cultural construct.

ES : You say in the book that something inside you broke when your parents were away working as doctors during the war. That certainly sounds like you're objectively identifying a mental problem.

OS : It meant I couldn't leap into my mother's arms when I saw her again. I treated her like a stranger.

ES : As a child, a life in science seemed to you a noble thing. Does your life count?

OS : I don't know whether my life qualifies me for nobility or whether it qualifies as science either. There is something noble about the single-minded pursuit of a question in science, but I have darted all over the place. This is partly just the physician's life. You respond as people reach out to you. Yet there may be some integrity in that I tried to bear honest witness as to how it is for people. This requires a duality. You have to look at the physiology, but also the nature of experience, the impact of the physiology on someone's life. This is the intersection of biology and biography. It forces me to use narrative. I have to tell stories. My patients tell me stories, and their stories have a certain value in terms of self-discovery.

ES : That reminds me of the part in the book where you talk about my great Grampa Sam (Oliver's grandfather) imitating his patients.

OS : He would also imitate his former boss Henry Head, a neurologist at the London Hospital. Henry Head developed Parkinson's and would totter the length of the ward and sometimes fall and have to be caught by one of his own patients. I remember Pop accelerating down Exeter Road in mimicry.

ES : I've seen you imitating your Tourette's patients.

OS : I can't think of Tourette's without wanting to imitate it.

ES : Do your patients mind?

OS : If they feel it's sympathetic, they may even imitate themselves. One of my former students mentioned in the preface to his book how he came to work with me in New York for a few weeks and how shocked he was when I burst out laughing in front of a patient, and how the patient then joined in. It is legitimate to laugh. There are moments of real comedy mixed into the horror, and it's OK to recognise this.

ES : Why did you decide to write Uncle Tungsten ?

OS : It was a nostalgic effort to re-enter what Henry James called "the unvisitable past", to have it again. I'm glad I've written it. I feel more rooted. There really was a childhood. I didn't jump out fully formed. I'm not too certain about the continuity between the periodic table number-loving self and, as you say, a person who today works with the complexities of the subjective, but I've no impulse to write a volume two. I also felt there was a certain historical value. This is a book about someone growing up in a large and scientific Anglo-Jewish family in the 1930s, and the effects of war and evacuation on the family.

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Uncle Tungsten is published by Picador, ?17.99.