Italian scientists have shed new light on the biological mechanisms in the brain behind phobias and addictions to eating, alcohol and drugs.
The Rome University team believe the advance could open new doors for the development of drugs to treat these forms of compulsive behaviour.
"We have discovered that the positive motivation to do something, eating for example, is dependent on the production of a chemical compound called noradrenaline in the prefrontal cortex of the brain," explained Professor Stefano Puglisi-Allegra.
"This process, therefore, is also behind excess behaviour, such as overeating".
He said that the same is true for negative motivations not to act, which can become phobias when the sufferer develops an irrational aversion to something.
"Naturally this is just part of a mechanism which is much more complicated," Puglisi-Allegra added.
"But it shows us the way to a very promising road. Before we thought this process took place in another part of the brain
Noradrenaline is a neurotransmitter - a chemical that relays and modulates electrical signals between neurons and other cells.
The prefrontal cortex is important because it is thought to be the part of the brain where we differentiate between conflicting thoughts, determine good and bad, predict outcomes and prioritize goals.
The Rome University breakthrough is the result of tests on laboratory mice.
The mice were given chocolate and cocaine (both pleasant stimulants) and lithium chloride (an irritant) in different settings, so their brains could associate the places and the sensations provoked.
Puglisi-Allegra's team then measured the level of noradrenaline produced in different parts of the brain.
"It was important to measure the reactions in different environments," explained Puglisi-Allegra.
"This is because environment is a fundamentally important factor for human emotional responses and when these responses are excessive, they can cause compulsive behaviour.
"The study has given us some important clues about the role of neurotransmitters.
"An excessive biochemical reaction overloads the brain structures concerned, making the mechanisms less flexible, which leads to addiction or phobia".
Some medicines already treat these disorders by working on neurotransmitters, the professor said.
"But more in-depth knowledge of the processes and the parts of the brain involved will make it possible to do research on better-targeted therapies," Puglisi-Allegra concluded.
The study has been published in the latest edition of prestigious US journal, Proceedings of the National Academy of Sciences.
