Scientists believe that stem cells offer a realistic hope of treatments for Parkinson's disease.
Pioneering research could help Parkinson's patients
At a conference of stem cell experts in London on Monday, Professor Olle Lindvall said that cell transplants could help halt physical decline.
Stem cells are the body's "master cells", and could be transformed into new brain cells to replace those lost to illness.
The Swedish researcher warned that treatments could take time to arrive.
Professor Lindvall, from Lund University, is one of Europe's most respected experts in stem cells.
He was addressing a meeting of more than 500 stem cell researchers organised by the UK Medical Research Council.
Patients with Parkinson's disease have lost large numbers of a particular key type of brain cell that produces a chemical needed for the body to control muscular movements.
As a result, patients often suffer from stiffness, fatigue and involuntary movements.
Professor Lindvall said that research using a type of stem cells taking from aborted foetuses had already shown that it was possible to improve symptoms by partially replacing the cells lost to the disease.
However, the supply of such cells is extremely limited, he said, and his eventual hope is to use cells from the early embryo instead.
These cells have the ability to be transformed into cells to make up any type of tissue in the body, including bone, blood and brain cells.
However, embryo stem cell research remains controversial, as many individuals and groups are opposed to the use of embryos in this way, whether they are "left over" from IVF or specially-created to match the transplant patient.
There are hopes that eventually, cells from adults could be "persuaded" by chemicals in the laboratory to behave more like embryonic or foetal stem cells.
However, scientists do not yet fully understand how to use chemicals to "prompt" the cells to convert into the type of cells they need for a transplant.
He said: "Stem cells could be potentially useful for the treatment of Parkinson's disease - but it's a very difficult problem to generate large numbers of dopamine-producing neurons, which are the cells we need.
"I am convinced that stem cell technology can become, in the future, a cure for conditions leading to brain injury - but I think we have a long way to go."
His own research in Sweden, however, offered the tantalising prospect of a brain which - with some encouragement - could actually repair itself when injured by a stroke or illness.
He has discovered that, in the rat brain, in the weeks after a stroke, new brain cells are produced and actually begin to "migrate" to the affected area.
This suggests, that if scientists could find out what triggers this process, then this natural healing mechanism could be encouraged by drug treatment, perhaps alongside stem cell transplants.