Electro-convulsive therapy wiped out 15 years of Jonathan Cott's memories. So he began piecing together his past - and exploring what it means to remember. Barbara Elizabeth Stewart meets him

In his books, he conversed with Glenn Gould, the great classical pianist; explored the mythic aspects of children's literature; and delved into the tale of a British scholar of Egyptian studies who was convinced she was the reincarnation of an ancient Egyptian temple virgin.

But in 1998, after his mother died, his depression turned into a crisis. He spent almost two years in psychiatric wards in New York City, where he lives. He received 36 electroshock treatments, or ECT.

Electroshock is probably the most controversial treatment for mental illness, having a lurid reputation among lay people. Many assume it is no longer used. But, while some mental-health professionals oppose ECT, others - and some patients - maintain that it can relieve depression rapidly and effectively, with few side effects.

Whatever the truth, its effects on Cott were catastrophic. ECT has caused him to forget 15 years of his life. He has almost no memory of the years between 1985 and 2000. Apart from a few snapshot-like scenes of highly emotional events, he has lost both his private and public memories of those years.

It's all gone - the friends he made, the books he wrote, his travels - trips to Edmonton in Canada and Lhasa in Tibet, and four summers in a red-painted cottage on the coast of Sweden. News events are gone, too. The end of the Cold War? The end of apartheid? The Reagan and Clinton presidencies? Nothing.

In recent years, he has filled himself in on the news by reading, although he had to relearn how to use a computer, and learn to use the internet. He has reconstructed his personal history by looking at snapshots, journals and poems. Mostly, though, he depended on friends to tell him what he couldn't remember.

"I was calling up names in my address book and asking, 'How do I know you?'" he says. "Fortunately, I have a sense of humour about it now. I'm always amused and amazed."

The topic of memory and his loss was an obvious choice for Cott to write about. But how do you write about what you don't remember? In his new book, he rises to the challenge. On the Sea of Memory: A Journey from Forgetting to Remembering is his response. It is a meditation on memory - what it is, what it does, how it makes us who we think we are. It investigates how memory seems to work, the damage - and the unexpected silver linings - created when it is lost.

He also explores group memory and the spiritual aspects of remembering, from the Torah's exhortation to Jews to remember their history to the Tibetan Buddhist idea of the remembrance of past lives.

At its heart is the question of what, exactly, it is to be human. Is memory the main link between the self of yesterday and today? If we forget, who are we?

At 62, Cott has a fragile look about him. When we meet, his hands shake; a result of the shock treatments, he says. These also damaged his quickness and ability to make connections, lowered his IQ and diminished his vocabulary. "There's a stock of words that have just vanished," he says. "It's a task to find the right words. It's like putting a sieve in water and trying to pull it up." He often has to settle for simpler, less precise words. But it could be worse: "I've heard of people who've forgotten they have kids. I'm grateful I can talk at all, and write at all."

He wrote the book because it was the subject uppermost in his mind. "I decided to get curious about memory and its structure. "I'd never thought about memory before. I took it for granted. But now I thought: what is it about memory that so important? What is it, anyway?"

In On the Sea of Memory, Cott poses questions to medical, psychological and spiritual experts. He talks to the actress Ellen Burstyn, a rabbi, a Christian minister, a Sufi master and a Buddhist Lama, as well as to neurobiologists and psychologists.

In between, he weaves his own story. The books he wrote during those lost 15 years are entirely new to him. He recounts a conversation with "my double, my brother" - Floyd Skloot, a writer who suffered a similar loss of memory after an illness and wrote about it in a book called In the Shadow of Memory. "There's tremendous benefit in discussing all this with you," Skloot said - and Cott feels the same way.

The limitation of Cott's book lies in the question-and-answer format. His memory problems forced him to stick to questions prepared in advance, rather than ranging off on to tangents.

At times, he did allow himself to range off. Talking to Judith Gleason, a New Yorker author who has written about African storytellers, Cott draws Walt Whitman, William Blake and Bruce Springsteen into the conversation, with rewarding and enriching results.

The 11 conversations on memory and Cott's own story take us into strange territory. That which we hold to be solid - our selves, our pasts - is anything but. Medical researchers are proving that even our most vivid memories may be false. In various studies, psychologists have been able to get adults to "remember" childhood incidents that are entirely fake, invented. They did not need to use hypnosis or other mind-control techniques; they simply described an invented incident convincingly and urged the adult to think back on it. Between one-quarter and one-third of the adults recalled getting lost while shopping or shaking hands with Bugs Bunny, the cartoon rabbit, when nothing of the sort occurred. They even added their own details to the stories.

These studies are sharpening the debate between the advocates of adults who say they have recovered memories of childhood abuse or Satanic rituals, and opponents who say that psychotherapists can introduce false memories through suggestion and inference.

On the other side of fake memories are sharp memories of traumatic events that sufferers cannot get rid of. University of California researchers say that obsessive "black hole" memories, created by painful events, embed themselves in the brain's circuitry; people relive them over and over, causing post-traumatic stress disorder.

Societies have long realised that painful occurrences can create powerful memories. In the past, illiterate communities created records of important events, like marriages and treaties, by instructing a child to observe the proceedings carefully - and then throwing him into the river or doing something similar to burn the memories into his mind.

The University of California experts have discovered that beta-blockers, used to treat migraines and heart problems, can diminish traumatic memories. But they only work if taken during or soon after the event, before the memory is able to make indelible inroads into the brain.

Cott tells of techniques for remembering that have been used from the ancient Greeks to the present. A Russian journalist, for instance, was able to remember long, meaningless mathematical equations. His method was to create characters and stories for every single number and dot. He had hit on a mnemonic device that dates back to Aristotle and Cicero, and is recommended today for people who habitually forget the names of people after being introduced.

Judith Gleason is the author of books on the West African griot: the bard who remembers and recites the tribe's history, culture and genealogy. Her interview centres on a kind of ancestral memory that is lost to most Westerners. "It's important to know where we've come from," Gleason says, "because the only thing that makes mortality tolerable is this sense of inheritance and continuity."

Though an African child has his own personality and soul, he is also a reincarnation of his parents and grandparents. To lose that is to be a "goblin", a spirit disconnected from human continuity. Thus, Gleason says, Westerners must find their own spiritual ancestors, the ancestors who speak to them through music, poetry and spirituality.

Sogyal Rinpoche, the incarnate Tibetan Buddhist Lama interviewed by Cott, describes a view of ancestral memory equally ancient but quite different. Sogyal's conversation covers much ground: reincarnation, the role of karma (or profound cause and effect) and what he calls the true nature of mind. He repeats one of the sayings of Padmasambhava, the ninth-century Indian saint who introduced Buddhism to Tibet. It seems sensible even to people who are sure that this is their one and only life: "If you want to know your past life, look to your present conditions; if you want to know your future life, look at your present actions."

For all of us, however well we can remember, memory is a reconstruction, Cott concludes. "I am always overjoyed when trying to reconstruct or imagine friends I once knew at specific times and memorable places in my disappeared world."

At the end of his book, Cott reproduces a note he wrote to himself when he was undergoing the shock treatments, which he had forgotten about until he found it in a file. "I am living in the moments of my days, the long thoughts and feelings cut down to more manageable lengths. I must learn to live in the present. Begin at zero. Start here."

'On the Sea of Memory: a Journey from Forgetting to Remembering' is published in the United States by Random House

What is electro-convulsive therapy?

* ECT became hugely popular in the USA and Europe in the 1940s and 1950s, but fell out of favour in the 1960s amid fears about the barbarism of the treatment.

* Techniques have changed and ECT is widely practised again. About 10,000 people receive it on the NHS each year.

* Guidelines say ECT should only be given if drug therapies have not worked, or if someone is a threat to their own safety.

* The patient is given a general anaesthetic. Electrodes are attached to the head and a small electric current is switched on for about three seconds, inducing an epileptic fit for a few minutes.

* When the seizure finishes, the patient is woken up. The treatment is repeated up to 12 times.

* It is not known exactly how ECT works. There are theories that it increases levels of feel-good chemicals in the brain, such as dopamine. It may also wipe out depressive patterns of thought.

* Opinion is still divided over its effectiveness and safety: one study concluded that it helped in 70 per cent of cases, while a UK Advocacy Network survey found that half of patients said it was unhelpful. About half of patients have problems with memory loss, although this is usually short term.

Maxine Frith