Lacey , 27 Apr 2016.
If you have a huge decision to make - maybe deciding who to vote for or whether to get married in Vegas? - don’t do it hungry. It turns out that ghrelin, a hormone produced by the stomach that rises before meals and makes you want to eat, negatively impacts decision-making and impulsivity (we talked about ghrelin before).
Impulsivity is core to many neuropsychiatric disorders, including attention-deficit/hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), substance abuse, autism spectrum disorder (ASD) and eating disorders.
Impulsivity is complex but can be broken down into impulsive action (inability to restrain a motor response) and impulsive choice (decision-making).
New open access research from the lab of Karolina P Skibicka at The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden published in Neuropsychopharmacology has demonstrated for the first time that ghrelin surges (like those seen before meals or when fasting) act on the brain to increase impulsive actions and choices. And not only that- these increases in ghrelin cause long-term changes gene expression in brain areas integral to impulsivity.
To go or not to go? Impulsive action is enhanced with an empty stomach
Not grabbing that delicious cookie five minutes before your dinner is ready can be hard: it involves waiting or a certain level of restraint.
This is true for rodents also. Rats can be trained to get a reward (like sugar) when they act by pressing a lever (“go”) or when they wait (do not press the lever; “no-go”). They learn this through cues- for instance a flash of light or a buzz sound will tell them what they have to do in order to get the reward. An inability to restrain themselves when given the wait signal to obtain the reward is a measure of impulsivity. The researchers found that after injecting ghrelin into the brain (mimicking how the stomach would communicate to us the need to eat or a meal-time) the rats were less restrained- they pressed the lever instead of waiting, and, ironically, this lead to them not getting their sugar reward.
An empty stomach drives desire for instant gratification
When given the choice of having a chocolate chip immediately verses four chocolate chips if you wait five minutes- what would you choose?
The ability to delay gratification for a larger reward is a measure of choice impulsivity- if you choose instant gratification (albeit with a lower amount of reward) then you could be characterized as being more impulsive than someone who waits for the larger reward.
Rats can be trained to basically make the same choice. The researchers found that more ghrelin acting on their brain prevented the rats from being able to wait for the larger reward- with the ironic result that the rats ended up with less treats because the instant reward was less!
Your empty stomach is messing with your brain reward system
Differential Reinforcement of Lower Rates of Behavior (DRL) is a behavioral method often used to control impulsive or unwanted behaviors, such as yelling out in class instead of raising a hand. Rewards (reinforcers) are offered if the number of times the unwanted behavior (yelling) is reduced. Of course rats don’t yell but when a similar test is applied to rats it can tell you something about impulsivity.
The researchers found that limiting ghrelin injections to a part of the brain that is involved in reward, called the Ventral Tegmental Area (VTA), was sufficient to make rats more impulsive. And, the opposite happened when they blocked ghrelin- impulsive behavior reduced by half!
For all of you thinking “who cares? Nobody is injecting ghrelin into my brain”! Well, food deprivation (a more natural way to increase ghrelin release) also increased impulsive behavior.
The VTA contains the reward neurochemical dopamine (also a target of drugs of abuse) and is part of a larger brain circuit that is responsible for reward seeking behaviors, including impulsivity. Interestingly, humans with ADHD and OCD have less enzymes responsible dopamine turnover and changes in dopamine related genes in parts of the brain associated with impulsivity. The researchers found that the ghrelin injection into the brains of rats that resulted in impulsive behavior also caused these changes in dopamine related genes and enzymes.
In the future, targeting ghrelin receptors in the brain could be an avenue for treating psychiatric disorders that have impulsivity problems (including food or alcohol disorders). Or maybe modifying meal times and increasing snacking as a way to control ghrelin spikes could be a method for improving impulsive behavior. Remember this before making an important decision or before a big night out!
To view the original open access paper discussed in this blog “The Stomach-Derived Hormone Ghrelin Increases Impulsive Behavior” in Neuropsychopharmacology click here.
The Blog was written by Carolyn Lacey, Scientific Outreach Manager at Neurexpert. To learn more about Carolyn and Neurexpert, please click here.
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