Never make a decision when you are hungry, warn scientists who have found that a hormone known to increase appetite negatively affects decision making and impulse control.
Researchers found that higher levels of ghrelin prevented the rats from being able to wait for a greater reward.
"For the first time, we have been able to show that increasing ghrelin to levels that are seen prior to meals or during fasting, causes the brain to act impulsively and also affects the ability to make rational decisions," said Karolina Skibicka, from the University of Gothenburg in Sweden.
Many have experienced the difficulty of resisting getting a sandwich or something else, even if we know that dinner will be served soon, and the same is true for the rats used in the study, researchers said.
Impulsivity is a distinctive feature of many neuropsychiatric disorders and behaviour disorders such as ADHD, obsessive compulsive disorder (OCD), autism spectrum disorder (ASD), drug abuse and eating disorders.
The study also showed that increased levels of ghrelin even caused long-term genetic changes in the brain circuits that are linked to impulsivity and decision making.
A ghrelin injection into the brain that resulted in impulsive behaviour in rats, caused the same type of changes in dopamine related genes and enzymes as can be seen in ADHD and OCD.
"Our results indicate that the ghrelin receptors in the brain can be a possible target for future treatment of psychiatric disorders that are characterised by problems with impulsivity and even eating disorders," said Skibicka.
Rats can be trained to be rewarded (with sugar) when they execute an action such as pressing a lever ("go") - or instead they can be rewarded only when they resist pressing the lever ("no-go") when an appropriate learned signal is given.
They learn this by repeatedly being given a signal, for example, a flash of light or a buzzing sound that tells them which action should be executed for them to receive their reward.
An inability to resist pressing the lever, when the "no-go" signal is given, is a sign of impulsivity.
Researchers found that rats given ghrelin directly into the brain, which mimics how the stomach would notify us of a need to eat, were more likely to press the lever instead of waiting, despite it causing them loose their reward.
The person who chooses immediate gratification even though
waiting provides a greater reward, is characterised as being more impulsive and that implies a poorer ability to make rational decisions.
"Our results showed that restricting ghrelin effects to the ventral tegmental area, the part of the brain that is a crucial component of the reward system, was sufficient to make the rats more impulsive," said Skibicka.
Even a short period of fasting, a more natural way of increasing the release of ghrelin, increased impulsive behaviour.
