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Impulsive decisions can be triggered by high levels of ghrelin, when humans are hungryGetty Images

Taking a decision while hungry is not a good idea, scientists have explained. This is because the hormone ghrelin increases our appetite in a way that may negatively affect our impulse control and our ability to make rational decisions.

The study, published in Neuropsychopharmacology, looks at how ghrelin – which is released before meals and induces our feeling of hunger – interacts with our ability to make rational judgements.

Conducted by scientists from the University of Gothenburg, the research involved measuring impulsiveness in rats, depending on their ghrelin levels.

Ghrelin and fasting

The rats were either trained to press or resist pressing a lever, in exchange for a food reward. Pressing the lever when they had been taught to resist this urge was considered by the scientists as a sign of impulsiveness and of poor rational decision-making skills.

Some of the rats were injected ghrelin directly into their brains, replicating how the hormone would normally behave when they were hungry. The scientists observed that these hungry animals had much more difficulty fighting their impulses and pressed the lever more frequently.

The researchers point out this behaviour is not unlike the one people have when they are hungry and make themselves a sandwich, even when they know dinner will be ready soon.

Findings were similar for rats who were put through a short period of fasting - which is a natural way of increasing the release of ghrelin.

In the brain

The researchers further evaluated in which part of the brain ghrelin acts to affect impulsivity. The animals made more irrational and impulsive decisions when ghrelin was injected in an important brain region involved in rewards.

"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. Importantly, when we blocked ghrelin, the impulsive behaviour was greatly reduced," says lead researcher Karolina Skibicka.

Additionally, an analysis of the rats' brains showed increased levels of ghrelin induced alterations to the brain circuits linked to impulsiveness and decision-making. The genetic changes involved were even similar to those noted in impulsiveness-related disorders like ADHD.