What happens when we’re hungry?

Hunger can affect more than our mood
It can also influence our willingness to engage in risky behavior

© Madelyn Griffith-Haynie, CTP, CMC, ACT, MCC, SCAC

Hunger and the Brain

You have probably noticed that being hungry can affect your overall mood and feelings of well-being — and that hungry people are often difficult to deal with.

Memes all over the internet frequently
describe that feeling as “hangry.”

But did you know that hunger can also influence the way you respond and make decisions, encouraging you to engage in risky behavior? This reaction can be seen in a wide range of species in the animal kingdom.

Experiments conducted on the fruit fly, Drosophila, by scientists at the Max Planck Institute of Neurobiology have shown that hunger not only modifies behavior, but also changes the use of neural pathways, revealing that hunger affects decision making and risk perception.

For those who don’t understand why scientists bother studying fruit flies:

1. the fruit fly is a wonderful genetic model organism for circuit neuroscience (studying connections) and gene/behavior influences.  (Model organisms that are especially valuable when similar early-stage research simply could not be carried out in humans);
2. their extremely short life-cycle allows research labs to observe effects over many generations quickly – in an extremely cost-effective manner;
3. their small size means that the equivalent of the entire population of a city like New York could be kept on a measly stack of trays in a single laboratory
4. scientists and labs usually don’t have to overcome a public perception problem.  Except for incredibly ignorant comments like the ones made by Sarah Palin when she complained loudly about “totally wasted research funds” during the 2008 Presidential campaign, very few educated people rally to object to research on fruit flies.

Related posts:
A Lesson for Sarah Palin on Fruit Fly Research – YouTube
Mapping behavior in the fruit fly brain — ScienceDaily

Source: Science Daily, found HERE

DID YOU KNOW THAT, among other things . . .

…they can be used to study sleep — that coffee keeps them awake, and that old fruit flies sleep less than young ones?

…the first “jet lag genes” were found in these flies, which aided in their discovery in humans?

…the first learning genes were discovered in fruit flies and operate in the same manner in humans?

…in fact, about 75% of human disease genes have a recognizable match in fruit flies? (i.e., “Homologous” – having the same or a similar correspondence, as in relative position, structure and/or function)

…since they can get drunk and addicted to alcohol, they have been immensely helpful in addiction research?

…they have advanced our understanding of cancer, epilepsy & Alzheimer’s enormously and can be used to help develop future medicines for these conditions?

…they have functionally similar stem cells and have taught us a great deal about their behavior and regulation?

…they lead the way in dietary research, helping science discover what to eat for healthy ageing?

…Drosophila is the insect behind 10 Nobel laureates in Physiology or Medicine?

Source: Why the fly? | Manchester Fly Facility

And NOW they are helping scientists study the effect of hunger and nutrition on behavior.

Field observations and studies of other lab animals have shown us that the willingness of many animals to take risks increases or decreases depending on whether or not the animal is hungry. (For example, a predator in the wild only hunts more dangerous prey when it is close to starvation.)

In recent years, this behavior has even been documented in humans: one study showed that hungry subjects took significantly more financial risks than their colleagues who had eaten their fill.

In addition, it seems that the fruit fly, Drosophila, changes its behavior depending on its nutritional state.

But how does that work in the brain,
and what can we learn from it?

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What we are learning from fruit flies

Max Planck Institute (from their website)

Facing the prospect of food, hungry animals of all types seem to be significantly more willing to take risks than sated ones.

Researchers at the Max Planck Institute of Neurobiology in Martinsried, at the southwest border of Munich, conducted several interesting experiments to find out why and how.

Testing their theory that certain decision-influencing nerve cells are activated and deactivated by different levels of hunger, they analyzed signals in the brains of fruit flies that were put in a situation where hunger was combined with a normally threatening situation.

Source: SciTech Daily, Hunger and the Brain

Animals usually perceive even low quantities of carbon dioxide to be a sign of danger. However, the fruit flies’ main sources of food also release carbon dioxide — rotting fruit and other plants.

HOW does the brain differentiate to make those behavioral decisions?

© Phillip Martin – artist/educator

To begin to explore the question, researchers put fruit flies in environments containing carbon dioxide alone or a mix of carbon dioxide and the smell of food.

They learned that the hungry ones overcame their aversion to carbon dioxide significantly faster than the well-fed ones – as long as there was a smell of food in the environment at the same time.  NOT so great where staying alive is concerned.

By taking advantage of the ability to make changes in the brain of a large sampling of fruit flies, neurobiologists at the Institute have now discovered how the brain deals with the decision conflict between a hazardous substance and a potential meal.

Scientists believed that two different areas of a fruit flies’ brain controlled different aspects of their behavior, so the researchers disabled each area individually to see how their behavior changed.

By temporarily disabling the area used for learning and making decisions (“the mushroom body”), they found that, when hungry, the flies showed no reaction to the danger of carbon dioxide.

Those hungry fruit flies went about their business as usual, despite the fact that carbon dioxide was present.

But how does the brain manage to decide between these options?

Previously, the nerve cells in the mushroom body were thought to be linked only with behavior patterns that are based on learned associations. Avoiding carbon dioxide is an innate behavior, so was expected to be generated outside the mushroom body in the fruit fly’s brain.

Remember, however, that when the scientists temporarily disabled these particular nerve cells, hungry fruit flies no longer showed any reaction whatsoever to carbon dioxide. The behavior of fed flies, on the other hand, remained the same: they avoided the carbon dioxide.

Found HERE

In further studies, the researchers identified a projection neuron that transports the carbon dioxide information to the mushroom body.

This projection neuron forwards carbon dioxide information to the region in the fly’s brain where the animals can gauge internal and external signals.

This nerve cell is crucial in triggering a flight response in hungry, but not in fed animals. (Purayil & Kadow for the Journal Neurobiology).

“In fed flies, nerve cells outside the mushroom body are enough for flies to flee from the carbon dioxide. In hungry animals, however, the nerve cells are in the mushroom body and the projection neuron, which carries the carbon dioxide information there, is essential for the flight response.

If mushroom body or projection neuron activity is blocked, only hungry flies are no longer concerned about the carbon dioxide,” explains Ilona Grunwald-Kadow, who headed the study.

The results show that the innate flight response to carbon dioxide in fruit flies is controlled by two parallel neural circuits, depending on how satiated they are.

“If the fly is hungry, it will no longer rely on the ‘direct line’ but will use brain centers to gauge internal and external signals and reach a balanced decision,” explains Grunwald-Kadow.

“It is fascinating to see the extent to which metabolic processes and hunger affect the processing systems in the brain,” she adds.

____________________
Source: Max Planck Institute — Publication: Lasse B. Bräcker, K.P. Siju, Nelia Varela, Yoshinori Aso,
Mo Zhang, Irina Hein, Maria Luisa Vasconcelos, Ilona C. Grunwald Kadow, “Essential role of the mushroom body in context dependent CO2 avoidance in Drosophila,” Current Biology, June 13, 2013, DOI:10.1016/j.cub.2013.05.029

 

What does this mean for human beings?

Quite possibly, this information could make a huge difference between success and failure, happiness and unhappiness, or states of calm and high-anxiety.

Since hunger seems to shift decision making between different parts of the brain, altering the natural fight or flight reflex in response to danger that is shared by many animals, these fruit fly studies have implications for many other stresses of modern life for most of us.

Stress impacts our brain’s “danger” mechanism.
Hunger is extremely stressful, even if we don’t realize it.

Satiated individuals are hypothesized to react more strongly to risk-aversion than hungry individuals, albeit below conscious awareness in both cases.

In hungry individuals, the brain’s response to its desire for sustenance well may override perceived danger in areas besides food gathering.

In other words, in response to the below-conscious-awareness perception of “danger” when we skip meals, we’re likely to take more chances, engage in more risky behaviors, and make more decisions we later regret.

Since it also seems that inadequate nutrition plays a role in the brain’s perception of hunger, a diet of junk food may well promote similar ill-advised behavior.

Yet another good reason to
watch what we eat?

Check out Sally Cronin’s excellent nutrition series on her Smorgasbord Invitation blog for ton’s of great information intended to help us make better choices (always available from the second line of her top menubar).

The two below will get you started:

* The basic shopping list for your body’s nutritional needs
* Nutrient directory and the foods that supply them

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Related Articles ’round the net

• How studying fruit flies and zebrafish might unlock secrets of the human brain [PBS]
• Why skipping lunch could make you a liability: Hunger affects the fight-or-flight reflex and triggers  risky behaviours
• Hunger enhances consistent economic choices in non-human primates
• Fruit fly brains shed light on why we get tired when we stay up too late
• Ritu’s Healthy Eating – 13 Tips Learned Over The Last Year
• Hunger in America Study findings
• The psychology of hunger – American Psychological Association
• Hunger and Thirst: Issues in measurement and prediction of eating and drinking (study)
• The Dutch Hunger Winter and the developmental origins of health and disease (study)
• The Risks of Hunger. It Makes You Take More Risks.
• The Risks and Rewards of Skipping Meals
• Mood, food, and obesity (study)
• Always Gamble on an Empty Stomach: Hunger Is Associated with Advantageous Decision Making (study)
• American Adolescents Suffering From Hunger Have A Higher Risk Of Mental Health Problems

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