Hunger Hormones Lead To Impulsive Decision-Making

Our ability to rationalize and make good decisions can be adversely impaired once a single hormone is produced when we experience hunger, according to a team of researchers at the Sahlgrenska Academy, University of Gothenburg, Sweden. Findings showed that rats given the ghrelin hormone were more likely to act on impulse:

“Ghrelin is one of the main hormones to stimulate hunger, and is produced by specialized cells that line the stomach and the pancreas. Ghrelin levels increase before meals and decrease after meals, a mechanism that has its roots in the hypothalamus. If the lateral hypothalamus is removed (as seen in animal studies), feeding becomes less frequent leading to severe weight loss and death. If the ventromedial hypothalamus is removed, feeding increases, leading to weight gain and severe obesity.” defined by Dr Ananya Mandal, MD in News Medical.

Affecting us all, impulsivity is broken down into two categories: impulsive choice; an inability to delay gratification, and impulsive action; the inability to stop one’s self from making a physical action.

The ability to forgo something desired now, for something with future gratification, shows control.

Although links between impulsivity and various psychiatric conditions is undeniable, there is still a void for a proven mechanism within this very important physiological spectrum of study.

A new study, recently published in Neuropsychopharmacology, aimed to fill this void. Led by Karolina Skibicka, researchers set out to investigate the potential role of ghrelin in impulsive behaviors by investigating the impulsivity in rats in relation to the hunger hormone.

Here’s how the study worked

Rats were trained to either press a lever to get a reward – referred to as a “go” signal – or they were rewarded for not pressing a lever – a “no-go” signal. The rats were taught to either “go,” or “no-go,” dependent on an auditory signal (a light or buzzer) in tests that measured the rats ability to restrain a response.

A second leg, dubbed the “differential reinforcement of low rate,” dispensed a food pellet reward for rats that were able to withhold their response for a set period of time.

The third trial, named the “delay discount,” measured the rats’ ability to delay gratification. The rats were presented with two levers, one of which would immediately dispense a single food pellet after it was pressed, while the other would incur a significant delay before dispensing a maximum reward of four food pellets.

If either lever was pressed, the other was blocked, teaching the rats to reject their initial impulse in order to receive the maximum reward later on.

Ghrelin was injected directly into the brains of the rats, duplicating how the hormone would normally behave when the animals were hungry.

As anticipated, the injected rats were unable to resist pressing the minimal reward lever in all three trials, proving that impulsivity had increased.

In fact, in the “go/no-go” trial, the rats were nearly three times more likely to press the lever during a “no-go” period when their brains were infused with ghrelin.

Researchers also found that fasting for a short period produced identical impulsive results in the rats.

“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 behavior was greatly reduced.” noted Karolina Skibicka, associate professor.

Skibicka hopes that, eventually, the brain’s ghrelin receptors could be a target for the “treatment of psychiatric disorders that are characterized by problems with impulsivity.”

These findings are the first to demonstrate the increased impulsivity that ghrelin produced in rats. Researchers hope that their findings might assist in the evolution of psychoactive drugs.