Dame Iris, who died in February aged 79, had suffered the disease for four years before her death.

Her husband, John Bayley is reported as saying that he and Dame Iris discussed the issue in the months leading up to her death.

The Alzheimer's Disease Society welcomed the couple's decision and said much research depended on such generosity.

Understanding the disease

Alzheimer's is a degenerative disease that slowly destroys brain cells.

Physical characteristics of the disease include plaques and tangles in the brain, but scientists do not know exactly how these relate to the dementia patients suffer.

Professor Robin Jacoby, who cared for Dame Iris at the Warneford Hospital in Oxford during her final days, explained how the donation would benefit research.

Donated brain tissue plays an important role in research

He told BBC News Online that first the brain had to be fixed in formalyn. This preserves the tissue in an unchanging state.

"Then microscope slides are made and the lesions of Alzheimer's disease are correlated with psychological deficits that were found in life," he said.

This helps researchers understand exactly how the disease works.

However, making the decision to donate one's brain to science would not have been easy in the end stages of a disease such as Alzheimer's, he said.

"In the final months it would be difficult for them to make a decision in principal, but in many cases people make these decisions in advance, before they become incapable of making decisions."

Generous donations

Harry Cayton, chief executive of the Alzheimer's Disease Society, said such donations were necessary to further understanding of the condition.

"There are a number of brain banks in the UK," he said, "and they're all dependent on the generosity of families in donating brains for research, an important part of our fight against Alzheimer's disease."

A high-profile donation also helped raise awareness of the need for continuing research into the disease, he said.

"It does help when people who are well-known in the public arena make a public decision or a public statement of this kind, and encourages the many families who have already donated and perhaps some who will do so in the future."

And it was not only diseased tissue researchers needed, he said.