Sacks addressed a crowded Fieldhouse auditorium last Tuesday, at the most recent Beatty Memorial Lecture. Speaking on "Neurology and the Soul," Sacks smilingly admitted, "I chose this ludicrous title to give me the freedom to talk about anything I wanted."

The invitation to Montreal represented a sort of homecoming for Sacks. He arrived here from England 37 years ago, and stayed a short time before continuing his medical career in the United States.

"When I came here as a young man, I was divided between the medical and scientific path, and another desire to write, to chronicle, to animate, to make portraits. Now, for better or for worse, they've come together in a way."

Sacks delivered an impromptu talk, more conversation than lecture, discussing his views on the deaf community, colourblindness, dualism and determinism, and the adaptation of the brain after injury. The common theme linking these disparate topics is his belief that brain and personality cannot be separate entities.

"There is a neural embodiment of everything in one, from sexuality to our highest spiritual and mystical inclinations. To see the soul as embodied is no indignity. It in no sense reduces the sense of self. I think it makes it more mysterious and more exciting."

In this way, he distinguished himself from famed McGill neurologist Wilder Penfield, "one of the last dualists among the great physiologists," according to Sacks.

"Our brains are ours in a way which our hearts and livers are not. Hearts and livers have an immunological identity but they don't have any personal identity. The identity  self, soul, whatever you want to call it  is constructed from the first. Our brains are suffused with our souls, with self-ness, and this is why if we get delirious or get Alzheimer's, the identity shows itself as so robust."

He told, for instance, of a patient he met early in his medical training who was dying of an infection. The patient was delirious, and Sacks spent several hours listening to the man's ravings.

"[It was like] being privy to a dream. In his delirium, he brought up characters, episodes, scenes, passions, fantasies, really the whole of a life in the hieroglyphic form of raving. This gave me the strong feeling that however much disconnection there was, he was still there as a person. It was not just a delirious brain, this was his delirious brain. The brain was him. It gave me a feeling of the robustness of personality and identity, neurally speaking, so that even in this destructive effervescence, he was still there."

Sacks approaches altered mental conditions much as an anthropologist might a foreign ethnic group. He notes as an example the unique culture formed among communities of the deaf.

"Deaf people [distinguish] two ways of looking at them: the medical or pathologizing way, and their own way. The word 'deaf' spelled with a small 'd' means 'hearing impaired,' a medical condition. 'Deaf' with a large 'd' implies a community, whose members have their own language, their own culture, who construct a world from their own centre. American Sign Language is not English on the hands, not pidgin English. It is a language in its own right, it has its own grammar, it is indigenous."

In the same way, Sacks is sympathetic to the blind who, after years or a lifetime of knowing only blindness, refuse medical offers of corrective surgery, and to the deaf who decline cochlear implants. We presume that recovery of sight or hearing would genuinely improve a blind or deaf person's quality of life. In fact, says Sacks, those whose sensory and mental states might be considered deficient adapt, both neurally and psychologically, to their conditions. The auditory cortex in the brain of one born deaf will develop as an accessory visual centre, and the visual cortex of one born blind will become instead an auxiliary tactile centre.

"The entire life experience of the deaf person has not included sound. Sound has no meaning and no potential meaning. [Their brains and their lives] have been richly and coherently and completely organized using other ways. I would not try and put someone in a different sensory world without making an extensive inquiry into what that might be like."

Sacks contends such medical intervention could be detrimental. One of his patients came to him after having cataracts surgically removed. As Sacks describes it, the patient was "thrown into a [state of] deeply chaotic sight," since his visual cortex had not developed to process optical stimuli.

Sacks is best known for the more extreme case histories he's dealt with, like the post-encephalitic patients physically and mentally transfixed for decades, revived briefly by pharmacological treatment with L-Dopa. One patient he called "Rosie" awoke to talk and sing in the vernacular of the 1920s.

"She said, 'I know it's 1969, but I feel it's 1926.' She indicated that although certain flashbulb memories had been taken in, like Pearl Harbour or Kennedy's assassination, she had no sense of continued existence, of autobiography, for 43 years."

He's written of a successful abstract expressionist painter, celebrated for his use of colour, who became colourblind following an accident. Initially in despair, the artist resumed his work to critical acclaim for a "remarkable black-and-white period." He describes a surgeon whose mind and body while in the operating room defy Tourette's syndrome, allowing him to perform delicate procedures without the slightest bodily tic.

The stories of all of his patients are, to Sacks, powerful affirmations of human mental capacity and adaptability.

"It's important for me to communicate these strange case histories as exemplars or parables of the possible. My feeling is that we are built to survive. People learn ways of surviving or discover or create ways of surviving in almost any circumstances. I think I just multiply stories of complexity and survival, and hope that someone will make some sense of it."