In the past, researchers investigating appetite and satiety have had to rely on subjective methods like asking human subjects how hungry they feel at any given moment, or watching how much is eaten. These are considered to be rather unreliable, especially as appetite can be altered by other factors such as mood. But scientists at Imperial College in London and Kaohsiung Medical University, Taiwan, believe their brain-scanning method, which uses magnetic resonance imaging, to be a far more objective. If work currently underway to extending it from mice to humans is successful, it could far-reaching implications for countering obesity. "Appetite and appetite control are important components of why people put on weight," said corresponding author Professor Jimmy Bell of Imperial College. "We know very little about the mechanisms behind these processes and why they can vary so much between individuals." For a study using the technique published in the latest Journal of Neuroscience, Bell and team gave a group of mice one of two types of hormone: pancreatic peptide YY (PYY), which is known to inhibit appetite, or ghrelin, which increases it. They were also given a contrast agent of manganese ion. The researchers then used the imaging method to look at the part of the brain's hypothalamus that has already been established as playing a part in regulating appetite. They found that contrast agent was taken up by the neurons when the mouse felt hungry, so that they were lit up on the scan and the researchers could actually see them firing. By contrast, when the mice felt less hungry the neurons became less active and the signal decreased. In fact, the use of contrast agents to look at the anatomy of different cells. But this is said to be the first time a contrast agent that is taken up by hunger neurons has been identified - and therefore the first time researchers have been able to observe their response to different stimuli. Obesity is recognised as having reached epidemic proportions in the Western world. According to the figures prepared by the International Obesity Taskforce, there are variations in prevalence of obesity (body mass index of BMI over 30) across Europe but there is a marked upwards curve. Population obesity rates range from 10 per cent to 27 per cent in men and up to 38 per cent in women.