“Hangry” is slang for that feeling of anger you may get when you’re hungry. It’s very common, in my experience… My friendly advice: don’t make any important decisions when you’re hungry. Why? Because you’re more likely to act on an impulse. And this is not just a personal conclusion: this was actually the main finding of a study carried out at The Sahlgrenska Academy of the University of Gothenburg in Sweden, and recently published at Neuropsychopharmacology.

Impulsivity is a form of impaired decision-making wherein decisions are made with a lack of ability to plan for the future. Broadly speaking, impulsivity includes two components: impulsive actions and impulsive choices. These impulsive behaviors are characteristic of many psychiatric and behavioral disorders, such as gambling, substance abuse, eating disorders, for example. Research on the neurobiological mechanisms of impulsivity has established a role for some major neurotransmitters, including dopamine and serotonin.

But where does hunger fit into this? Apparently, the gut has a word to say when it comes to impulsivity. Both dopamine and serotonin are known to be modulated by a hormone that is produced by the stomach – ghrelin. Ghrelin is an appetite stimulant, which means that its levels increase during the initial period of food restriction, and this increase acts as a trigger for hunger, thereby leading to food intake. Ghrelin also increases the rewarding feeling of food through the action of dopamine and opioids. Food reward is in turn known to be positively correlated with impulsivity. And ghrelin seems to influence dopamine release in areas of the brain associated with increased impulsivity in humans. Ghrelin can also increase the levels of dopamine and the activity of dopaminergic neurons in areas of the brain associated with motor control and is thereby potentially associated with motor impulsivity.

Take together, this suggests that ghrelin may theoretically act as a neurobiological regulator of impulsivity. And that was precisely what the study mentioned above aimed to determine. The authors assessed the role of ghrelin on impulsive behavior, namely on the ability to inhibit or restrain a behavioral response and to delay gratification.

Their work showed that ghrelin increases impulsivity in rats that had to perform different tasks of impulsive responding, being able to affect both impulsive actions and impulsive choices. When a large food reward could be obtained without delay, ghrelin administration predisposed the animals to selecting that larger food reward; nothing surprising here – more food sounds like an obvious choice. But when obtaining a larger reward required waiting, a smaller but immediate reward became preferred. This revealed that ghrelin administration led to an inability to delay gratification, which is a manifestation of impulsive behavior.

Ghrelin’s association with dopamine release was also studied and it was shown that ghrelin administration led to an increase in the levels of dopamine in areas of the brain associated with impulsive behavior. Ghrelin treatment caused a reduction in the expression of an enzyme responsible for dopamine degradation, consequently leading to an accumulation of the neurotransmitter in that area. Reduced activity of that enzyme (Catecol O-Metiltransferase – COMT) is actually associated with attention-deficit/hyperactivity disorder and obsessive-compulsive disorder in humans, two conditions in which impulsive behaviors are paramount. This sustained the hypothesis that ghrelin’s effect on impulsivity occurs, at least partially, through the action of dopamine.

Besides explaining why we become so impulsive when we need food, this study also establishes another link between the gut and the brain: it shows how a gut-produced hormone regulates neurobiological mechanisms of impulsive behavior.

So, remember: whenever you get “hangry”, you can blame it on ghrelin. I sure will!

References

Abizaid, A. (2009). Ghrelin and Dopamine: New Insights on the Peripheral Regulation of Appetite Journal of Neuroendocrinology, 21 (9), 787-793 DOI: 10.1111/j.1365-2826.2009.01896.x

Anderberg, R., Hansson, C., Fenander, M., Richard, J., Dickson, S., Nissbrandt, H., Bergquist, F., & Skibicka, K. (2015). The Stomach-Derived Hormone Ghrelin Increases Impulsive Behavior Neuropsychopharmacology, 41 (5), 1199-1209 DOI: 10.1038/npp.2015.297

Bizot, J., Le Bihan, C., Puech, A., Hamon, M., & Thiébot, M. (1999). Serotonin and tolerance to delay of reward in rats Psychopharmacology, 146 (4), 400-412 DOI: 10.1007/PL00005485

Cheuk, D., & Wong, V. (2006). Meta-analysis of Association Between a Catechol-O-Methyltransferase Gene Polymorphism and Attention Deficit Hyperactivity Disorder Behavior Genetics, 36 (5), 651-659 DOI: 10.1007/s10519-006-9076-5

Menzies JR, Skibicka KP, Leng G, & Dickson SL (2013). Ghrelin, reward and motivation. Endocrine development, 25, 101-11 PMID: 23652396

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