Medicines can be used to treat diseases such as Alzheimer's and Parkinson's - but they must reach the brain itself to have a beneficial effect.

Specialists have so far been unable to get drugs safely and effectively through the organ's protective barriers.

One drug which could be used in the treatment of Alzheimer's disease, nerve growth factor, does not work if it is injected. Other methods of using the drug have proven costly and risky.

However, an article in New Scientist magazine reports that the nose can act as a highway to the brain.

Direct link

Dr Wiliam Frey, a neuroscientist in Minnesota, USA, saw potential in the fact that the nose is a direct link between the brain and the outside world.

"I knew that bad things could get in this way," he says.

"It occurred to me that maybe good things could get in this way too."

This is because the nerves between the nose and the brain - the olfactory nerves - are unusual.

Getting drugs to the brain has long been a goal for doctors

They run straight from the brain to the nasal cavity, which means they come into direct contact with the air.

This has been dangerous because it allows viruses to bypass the body's usual defences and sneak into the brain.

But now the peculiar relationship between nose and brain could be used to get medicine to parts of the brain affected by Alzheimer's disease, Parkinson's disease, multiple sclerosis and strokes.

Drug tests

Dr Frey tested nose drops containing nerve growth factor on animals and discovered that the drugs made their way past the olfactory section of the brain and into areas not directly involved in smelling.

This was in contrast to animals injected with the medication. With them, very little of the drug made it to the brain.