When a man dies no one can substitute him. He is dead, and no one can think or feel or write about what he jaw, felt or thought, because that person was unique and no one saw the world quite like him. The tragedy is worse when that person had created a vision of the world than no one had conceived before him.

A neurologist is a human being who, by force of circumstance, is used to seeing the tragedy of many patients. He frequently sees a world that is uncertain and full of pain. What are the consequences of these premises? The uncertainty of the world is the origin of religion and philosophy and is the main cause of ontological anxiety. We will never know if we can answer the fundamental questions: those that really matter to us. This uncertain world is the only one we can live in. It is uncertain from the physicial point of view of (the uncertainty principle); uncertain from the biological point of view (Darwinism is just an approximation and chance is of fundamental importance in this system); and uncertain from the social point of view because we are never really sure what society expects from us and because most social systems are essentially unjust. The weather and the financial systems are complex unpredictable systems. Love is one of the most uncertain and anxiogenic states of human beings. When we find certainty in it, it seems almost like a miracle and after that comes doubt again.

Oliver Sacks came into literature with what Truman Capote called non-fiction fiction (In Cold Blood). That is: the narration of something real but totally unexpected. His first title was engaging: The Man Who Mistook His Wife for a Hat. His English was interesting in its syntax and the use of certain verbs, but the subject of his literature was the predicament into which certain neuro-psychiatric patients were thrown into, in the term coined by Heidegger. He studied exhaustively how patients would cope or not with their illnesses and the eerie description of the symptoms and signs was at the core of his literature. To perform this feat, Oliver Sacks had at his disposal an enormous physical and mental endurance; a vast curiosity that he could share with his readers; an outstanding medical, neurological and psychiatric understanding, and foremost, a profound empathy for the people who suffered these strange diseases.

The man who mistook his wife for a hat was a musician who was developing visual agnosia: a difficulty in recognizing by sight common objects or faces. Several other like cases were artfully described in that memorable book. Although probably not his very best book, it catapulted Sacks to fame mainly because of the uncanny subjects description and also because his English prose was distinctly unusual. Oliver Sacks was born in England, a place that would have been ideally suited for pursuing a career as a neurologist, for England was the cradle of clinical neurology and neurophysiology. Instead, he travelled to America and trained as a neurologist in California. Towards the end of his life, he wrote that in Los Angeles he became interested in motorcycles, and experimented with certain drugs. He was uncertain for a while about following an academic career or, in fact, any career. After graduation he moved to a sort of asylum or nursing home for chronic neurological and psychiatric patients in New York City, the Mount Carmel hospital, where he became deeply interested, indeed obsessed, by his patients at that institution, particularly by a man unable to move due to severe parkinsonism secondary to encephalitis lethargica, due to the 1918-1920 epidemic of Spanish influenza. He gave him a trial of levodopa, that had been recently introduced, for the treatment of Parkinson's disease, with a dramatic although transient improvement. The description of this patient was translated into a surprising movie: Awakenings, with the role of Oliver Sacks brilliantly played by Robin Williams, who was later to develop both Parkinson's and dementia in a kind of cruel cosmic joke.

Oliver Sacks realized then that writing was his true vocation and he dedicated the rest of his life to fulfill that longing. He was lucky enough to have found the subject of his writing, something that many writers never really achieve. From then on he became a writer who would write about unusual neurological patients. He became associated to the Mount Sinai Hospital in New York City and began seeing all types of neurological diseases, continuing all the while to study and learn about neurology, neuroscience and neuropsychiatry.

Oliver Sacks was anything but a conventional neurologist. He was not interested in diagnosis, as the great majority of neurologists are, and he did not care much for technological issues. He was obsessed with the symptoms, particularly uncommon symptoms, and also how the patient could cope with them. Over time, his curiosity expanded greatly and he wrote, perhaps his most interesting book, An Anthropologist in Mars. This is a title that reveals both his profound interest in human nature and the insight he could get into a sort of philosophical anthropology by the study of human beings with rare neurological disorders. Mars is the strange land where these strange neurological patients dwell. The anthropologist is Sacks himself.

His curiosity was insatiable. He reveals (and revels in doing so) to our perplexed eyes a number of patients with surprising pathologies. A retarded black child who is able to play the piano just by ear without ever having taken piano lessons. A girl who can draw horses and other animals from memory with surprising accuracy. Patients who have an uncanny ability to paint, to play a musical instrument, to sing, to dance, to make complex calculations and who are at the same time mentally retarded or autistic. A surgeon with Gilles de la Tourette syndrome who shows no tics while he is operating. A patient with Asperger syndrome who is very successful at running a farm because of her fondness of animals. A middle aged man with congenital cataracts who is not able to recover vision when the cataracts are removed, for he is simply too old to learn how to see and finally must take up his stick and dark glasses again. The world of the savants, the child wonder, the Wunderkind, the gifted in one area and subnormal in others, patients who have suffered a lesion of the left brain and have become artists with a dominant right hemisphere.

Oliver Sacks himself had a peculiar brain for a neurologist. Unlike most clinical neurologists he never published a case study for the sake of making a diagnosis of a rare disease or to discover a new sign or symptom or illness. Neurologists are pathologically obsessed with making an accurate topographic and etiologic diagnosis; in discovering new signs and, rarely, in the epidemiological or physiopathological analysis of a disease. Historically, neurologists have proposed hypotheses of brain function and have been interested in localizing function. Most however are happy with the concept that the brain is a mosaic of fairly well localized functions, and the modern idea of functional networks with several parts of the brain connected between them and working in concept is seen at some distance or even distaste. The advent of tensor diffusion techniques has forced a change in the idea of a precise localization, but recovery of function, for this reason, has remained a puzzling question for many neurologists. Oliver Sacks was not interested in any of these endeavors. His position was a sort of perplexed attitude to how the patients, with brain damage or brain dysfunction, coped with the difficulties in their daily activities.

Later in his literary career, his curiosity about the human response to their diseases did not diminish, but he added a profound empathy for the suffering of his patients. He wrote then about a whole Pacific island where a high proportion of the inhabitants are color blind, he wrote a sort of timid autobiography called: My Uncle Tungsten and a book about searching for rare plants in Oaxaca. His best books, An Anthropologist in Mars and Musicophilia, however, are impregnated with a profound knowledge of neuroscience and brain function and he proposes several new theories of his own.

The only other great fiction writer to use his knowledge of neuroscience was Santiago Ramón y Cajal. In his short story "The corrected Pessimist" (El Pesimista Corregido) he uses his vast knowledge of neuroscience to explain how a young doctor, probably himself, can acquire a new vision of the world through neuroscience. Oliver Sacks continued to write papers when he knew his last voyage was near. To paraphrase Albert Camus: The struggle itself toward the heights is enough to fill a man's heart. One must imagine Oliver Sacks a happy man.