US scientists say they have more clues to the way the brain remembers smells.
The researchers hope their findings may aid research into Alzheimer's
The team found that a cell type, discovered in the late 1800s but never studied, has unusual properties that help the recognition of smells.
The study in the journal Neuron found the cells, called Blanes cells, could retain information about a smell, and magnify the brain's reponse to it.
The process by which these cells store memories is probably replicated in other brain areas dealing with memory.
The perception of smell begins when odour molecules in the air interact with one of the millions of sensory neurons - or messenger cells - in the nose.
These then send a signal to the part of the brain concerned with smell - known as the olfactory bulb.
It is here where the work of recognising that smell begins.
One of the puzzling aspects of smell is how our perception of an odour can evolve over multiple sniffs.
The latest research, by Case Western Reserve University in Cleveland, Ohio, suggests that Blanes cells play a key role because they have a unique ability to maintain their activity between sniffs.
Lead researcher Professor Ben Strowbridge said: "These cells are important because they are part of the circuit through which we recognise smell.
"The individual cells retain a memory - information is being stored in the cells about the smell.
"It is very unusual to find a case where a cell can retain a memory itself."
The Ohio team studied the way Blanes cells functioned in slices of rats' brains by using a special infrared microscope to track electrical activity in the extremely thin projections that the cells use to communicate with other brain cells.
They found that the specific pattern of connections with other cells led to output signals leaving the olfactory bulb being magnified hundreds of times.
This appears to explain how Blane cells have such a disproportionately large impact in the olfactory system.
The researchers also found the way this part of the brain worked was very similar to the part of the brain that deals with a range of memories - the cortical brain region.
It is this part of the brain that is damaged in Alzheimer's disease.
Professor Strowbridge said: "This may explain the how smells can so often trigger memories.
"How the (Blanes) cell actually works is so similar to a major part of the brain that's affected in Alzheimer's.
"We hope by understanding what's going on here - we might find a window into another part of the brain that is much harder to study."
Earlier research suggests people who have difficulty in identifying smells are more likely to develop the degenerative brain disorder.
And more recently, smell tests have been added to the tools used to predict dementia risk.
Professor Edmund Rolls who heads Oxford University's Computational Neuroscience Laboratory said the most interesting finding of the study was that the Blanes cells had a capacity to store information.
But he said even though the study was well defined, it was carried out under very artificial conditions and so may not show the same effects in live rats or even humans.
"I don't think it's telling is very much about how smell works."