Never make a decision when you are hungry. The stomach hormone ghrelin, which rises before meals and during fasting, impairs both decision making and impulse control. That is the central finding of recent experiments carried out at Sahlgrenska Academy, University of Gothenburg.
Ghrelin is released by the stomach to signal hunger to the brain. In a controlled series of studies on rats, researchers increased central ghrelin levels to mimic the pre-meal or fasting state and observed clear changes in behaviors linked to impulsivity and choice. The experiments show that ghrelin not only boosts appetite and the rewarding value of food, but also undermines the capacity to resist immediate urges and to wait for larger, delayed rewards.
How impulsivity was measured
Impulsivity has several dimensions, commonly separated into impulsive action (the inability to withhold a motor response) and impulsive choice (preferring smaller immediate rewards over larger delayed ones). The research team trained rats in established behavioral tests that measure these facets of impulsivity:
- Go/no-go tasks, where animals must press a lever for reward on “go” signals but withhold pressing on “no-go” signals;
- Differential reinforcement of low rate (DRL) schedules, which reward animals for withholding responses over a set interval;
- Delay discounting tests, which offer a choice between a small immediate reward and a larger reward delivered after a delay.
When ghrelin was administered directly into the brain—replicating the stomach-to-brain hunger signal—rats showed more premature responses during no-go periods and reduced efficiency on DRL tasks. In delay discounting tests, ghrelin increased preference for immediate, smaller rewards over delayed, larger rewards. These results indicate that elevated ghrelin promotes both motor impulsivity and impulsive choice.
Where ghrelin acts in the brain
To identify the neural substrates responsible for these behavioral changes, researchers targeted the ventral tegmental area (VTA), a midbrain region with dopamine-producing cells that play a central role in reward and motivation. Increasing ghrelin signaling in the VTA was sufficient to heighten impulsive behaviors. Conversely, blocking ghrelin receptors centrally reduced impulsivity, improving performance on tasks that require response inhibition and patience.
Even short-term fasting, a natural means of raising circulating ghrelin, produced measurable increases in impulsive actions in the animals. These findings link everyday fluctuations in hunger signals with changes in decision-making processes and the tendency to act without sufficient deliberation.
Longer-term effects and clinical relevance
Beyond immediate behavioral effects, the study detected ghrelin-induced changes in dopamine-related gene expression and dopamine metabolism in brain regions that regulate impulse control. Some of those molecular alterations resemble patterns seen in neuropsychiatric conditions characterized by impulsivity, such as attention-deficit/hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD).
Impulsivity is a hallmark of many psychiatric and behavioral disorders, including ADHD, OCD, autism spectrum disorders, substance use disorders, and eating disorders. Because ghrelin influences both reward processing and impulsive behavior, ghrelin receptors in the brain present a plausible target for future therapeutic strategies aimed at disorders where impulsivity and disordered eating intersect.
Summary of findings
- Ghrelin, the stomach-derived hunger hormone, increases impulsive action and impulsive choice in rats.
- Central ghrelin signaling in the ventral tegmental area is sufficient to drive these changes.
- Blocking ghrelin receptors centrally reduces impulsive behavior.
- Short-term fasting elevates impulsivity, mirroring the effects of direct ghrelin administration.
- Ghrelin modifies dopamine-related genes and turnover, suggesting potential long-term impacts on neural circuits involved in decision making.
Source: Karolina Skibicka – University of Gothenburg
Original study: “The Stomach-Derived Hormone Ghrelin Increases Impulsive Behavior” by Rozita H. Anderberg, Caroline Hansson, Maya Fenander, Jennifer E. Richard, Suzanne L. Dickson, Hans Nissbrandt, Filip Bergquist and Karolina P. Skibicka, published in Neuropsychopharmacology (April 2016). The study used complementary behavioral tests in rats—DRL, go/no-go, and delay discounting—to demonstrate that central ghrelin signaling promotes impulsivity and alters dopamine-related molecular markers.
This summary presents the core experimental results and conclusions without external links. The image included is for illustrative purposes and was provided with the original article.