In the science news this week, scientists attempt to categorise smells, a parasite that stops mice being scared of cats, afternoon naps help young minds develop, and finally the prize-winning photograph of the Milky Way.
Humans sniff only ten different types of smell
Scientists have claimed that everything humans are able to smell can be divided in to just ten broad classes.
In a paper  published on PLOS One, and reported by the BBC , Professor Jason Castro, of Bates College, and Professor Chakra Chennubhotla, of the University of Pittsburgh, used a computerised technique to assess the characteristics of a wide range of different smells, and sort them in to “clusters”.
The researchers have likened this to the way we categorise colours – although the precise hue depends on the exact wavelength of the light we see, there are well recognised categories we use to distinguish broadly different wavelengths, e.g. red, yellow, blue etc.
The researchers used 144 mono-molecular odours, and analysed how typical descriptions such as ‘sweet,’ or ‘floral’ fitted in to a broad classification. The outcome of the analysis showed that all of the ‘odour profiles’ tested could be well defined by their proximity to one of ten clusters.
The ten proposed smells are:
- Fruity (non-citrus)
Previous attempts to categorise smells in this way have been met with scepticism – including work in the 1950s by scientist John Amoore, who proposed a theory which involved seven smell categories based upon molecular shape and size.
Speaking to the BBC however, Castro explains why this work is different.
“We have not solved the problem of predicting a smell based on its chemical structure, but that's something we hope to do…You have these 10 basic categories because they reflect important attributes about the world - danger, food and so on.
"If you know these basic categories, then you can start to think about building smells,” he said.
Parasite causes permanent change in mice which cancels their fear of cats
A microscopic parasite which is thought to affect up to a third of the world’s population, may cause permanent behavioural changes in mice, a study published in PLOS One reports .
The Toxoplasma gondii parasite is known to inhibit the fear response mice display when they detect the presence of a cat. Recent studies at the University of California, Berkeley have shown that even after they were cleared of the infection, mice no longer displayed a fear response when exposed to cat urine.
As cats typically mark their territory with urine, mice are able to use this as a marker to detect and avoid areas where there may be predators. The researchers discovered that uninfected mice displayed an aversion to the cat urine but not to rabbit urine, which was used as a control. They also found that the mice that were infected, or had previously been infected but were now clear of the parasite, walked freely around the test area.
The fact that the behavioural change persists even after the infection has cleared, could have significant implications for infectious disease medicine.
Wendy Ingram, the graduate student responsible for the experiment explained to the BBC  how this may relate to human medicine.
"Typically if you have a bacterial infection, you go to a doctor and take antibiotics and the infection is cleared and you expect all the symptoms to also go away.
"Now we have an example where there is no obvious damage done by the parasite, yet major changes in the neurobiology of the mouse remain after the parasite is gone," she said.
The way forward, she added, would be to look at all the antibodies present in a patient's blood.
Midday nap improves the memories of pre-school children
A nap during the day can help young children retain information they have learnt in the morning according to a study  published in PNAS last month.
The study involved 40 children aged three to almost five years old all of who attended pre-school classes, reported the Guardian . The children were asked to memorise the positions on a grid of images including a cat, an umbrella and a policeman. They continued with the activity until they could remember the positions of around 75% of the images.
The team of psychologists visited each child twice during the study – on one occasion the child slept for an hour or so between 1pm and 3pm, and on the other stayed awake for the day.
The researchers found that the children who had an afternoon nap had no change in their score of 75%, whereas those who had stayed awake fared much worse, with an average score of 65%.
"If they stayed awake they forgot more of the items they had remembered in the morning, whereas if they took a nap, they remembered all the items they had learned in the morning," said Rebecca Spencer at the University of Massachusetts in Amherst.
The findings appear to highlight the importance that sleep plays in consolidating memories.
The researchers also tested the children the following day, to check that the lower scores weren’t due to the children being less alert, but they found the scores did not change, suggesting that the daytime snooze was essential for the information to be stored.
"You often see children forced out of napping, and hopefully this will help parents and pre-schools to understand that maybe that's not the best decision, and that a nap is an important part of the day," said Spencer.
"This is the science that's needed to preserve nap time. If our goals are to prepare children for early education, the naps are consistent with that goal because it's really helping them to learn," she added.
Incredible image of the Milky Way is prize-winner
A photo taken by Australian photographer, Mark Gee, has been given first prize in this year’s Royal Observatory Greenwich Astronomy Photographer of the Year competition. The stunning image shows the Milky Way seemingly emerging from the Cape Palliser lighthouse in New Zealand.
To see the winning photo as well as some of the other contenders, have a look at the slideshow on the New Scientist website .