In a packed marquee at the Edinburgh Book Festival this summer, you could feel disappointment sweeping through the audience.

It was as if the tent was deflating before one's eyes. Speaking about the race to find a cure for Alzheimer's disease, neuroscientist Baroness Susan Greenfield had just told us that, given the failures of medical research in the past couple of decades, current avenues of investigation now seemed unlikely to come up with a solution. Hope of treatment, she said, still lay far in the future.

I won't have been the only one who had gone to her talk hoping to hear good news. Indeed, many of those around me were of an age more likely to be concerned about their own health than that of their parents' generation. For these listeners, the threat of dementia was growing uncomfortably close. Being told to wait was not unlike hearing a death sentence.

So when news broke last week that a team of scientists in Leicester may have found an answer to the root cause of Alzheimer's and other degenerative brain diseases, and are working on a drug that can reverse its effects, it wasn't hard to imagine the elation in households across the land. One excited scientist said this development "will be judged by history as a turning point". Less hubristic, however, was Professor Giovanna Mallucci, who led the Leicester team, and whose cautious enthusiasm was designed to dampen hysteria. "Now we know it's possible to develop a treatment, this is a starting point," she said, indicating that it would be at least another decade before their work could be turned into a pill.

Meanwhile, at a conference of the Royal Society of Medicine last week, Professor Claude Wischik, professor of old age psychiatry at Aberdeen University, told members that his search for a drug that will slow or even halt Alzheimer's was going well. Targeting an entirely different aspect of molecular dysfunction from the Leicester team, his company's compound, the snappy-sounding LMTX, has now reached the stage of phase three trials across the world - the final tests before a drug can be licensed. He believed his medication might be available in four or five years.

So was Baroness Greenfield wrong to be gloomy? One certainly hopes so. At the very least, she was unduly pessimistic, it seems, about the theories being worked on. Whether this stems from professional competitiveness, given the fresh lines of enquiry her own college at Oxford University are following, remains to be seen. It is more likely, though, that she simply knows how deep the gulf is between headlines that promise the answer to one's prayers, and harsh reality.

The ferocity of competition in medical research is eye-watering, hence the hype that attends each new discovery or advance. All neuroscientists are aware that whoever is first past the post will go down in history, most likely with a Nobel prize. Anyone who has been at a medical conference when a drug trial's disappointing results were announced will have seen how much rides on finding the magic bullet. Investors pull out, shares in the research company crash, and with it the confidence and reputation of the scientists whose hard work and dreams have come to nothing.

Far worse, though, is the effect such ­failures have on those desperate for a pill to combat arguably the most malign medical blight in the western world. There can't be many families in Britain that are not touched in some way by the effects of ­dementia or Alzheimer's. That's why misleading headlines are so cruel. As any scientist knows, the time lag between ­finding a potential cure and it making its way into your local chemist can be aeons. On average it takes 17 years between discovery and public availability, sometimes longer. When general anaesthetic was first discovered, for instance, it was 40 years before it was offered to anyone beyond women and children.

Yet what does seem irrefutable, offering tantalising but serious cause for optimism, is mounting evidence that the scientific world is at last closing in on degenerative brain disease. Various different routes are being followed, and who knows which will eventually be most efficacious. But there seems little doubt that finally - albeit painfully slowly - the fight is being won. In the meantime, what we all need is a cure for the agony of impatience.