A landmark British study has raised the prospect of a pill that can treat brain diseases such as Alzheimer's by halting the death of neurons.
The research, performed on sick mice, is at a very early stage and it could be a decade or more before any medicine suitable for patients is developed.
But experts say the findings are highly significant, and one predicted that they would be judged by future generations as an historic turning point.
The Medical Research Council (MRC) team focused on the root cause of many degenerative brain diseases, including Alzheimer's and Parkinson's - abnormally shaped proteins that stick together in clumps and fibres.
When enough misshapen protein builds up in the brain it can trigger a reaction that results in the death of nerve cells.
However, lead scientist Professor Giovanna Mallucci, from the MRC Toxicology Unit at the University of Leicester, warned that the drug in its current form has "toxic side effects":
We were extremely excited when we saw the treatment stop the disease in its tracks and protect brain cells, restoring some normal behaviours and preventing memory loss in the mice.
But we're still a long way from a usable drug for humans - this compound had serious side effects.
Leading Alzheimer's charity the Alzheimer's Society said the results of the study were "promising," but stressed that further research was required.