Humphrey is getting restless. It’s been two hours and he is starting to feel like he is going around in circles. He should sit and rest but it’s getting dark. He is lost. Very lost. There is no cell phone reception out in the woods.
After another twenty minutes of walking around and ending up in familiar surroundings, he sits down to try to think about what to do. He’s out of food but he has water, at least enough to last him until tomorrow if he limits his consumption. There are no predatory animals in these upstate Maine forests. It’s early September and the weather is still somewhat warm and will probably not get too cold at night. So, theoretically, he can survive until morning.
Humphrey curses his decision to hike alone, especially in a forest that doesn’t have any man-made hiking paths. Stupid, stupid, stupid, he says out loud. But, there is no point in looking back. He needs to think about resting and possibly getting some sleep.
His stomach growls. He hasn’t seen any edible fruits during his walk. He has seen some red berries but doesn’t know if they are safe to eat. He looks at his watch. It’s 6:15pm. He decides to rest for a little while and try again. He doesn’t have a flashlight but he could try using his cell phone for light.
Maybe I’ll be stuck here for a few days, he thinks. Not likely because he isn’t all that far from civilization. But he isn’t exactly thinking rationally. On the plus side, I could lose some weight if I don’t have anything to eat for a while, he thinks and smiles sadly.
What would happen to Humphrey’s brain and body if he is actually stuck in the forest for more than a few days?
He has been using up some of the stored energy in his body already. At this stage he is using the glucose which is absorbed from food and stored as energy reserve in the form of glycogen. Once he exhausts the supply of glucose, his system will switch to burning fat cells for energy. It will take a while before his body switches to the last source of energy, the stored proteins.
It’s the short term survival, however, that’s on the agenda for both the brain and the body as they work together to inform Humphrey that he is hungry. The body signals the brain when it’s hungry and when it’s full. It achieves this by sending messages to the hypothalamus.
Gherlin, a hormone produced by the stomach and pancreas, transmits signals of hunger. Its counterpart, the hormone leptin, tells the hypothalamus when the body is satiated and does not need any more food. As the body fill up with food, the amount of gherlin decreases and the amount of leptin activity increases. For Humphrey, his gherlin level is climbing higher and higher. In addition, a complex “orchestra” of hormonal and neural signals is helping the body to conserve energy. The leptin in his body will be in hibernation for a while until he has access to food.
Humphrey can probably survive without food for several days. Mahatma Gandhi was famous for subsisting for more than 20 days on nothing but sips of water. Michael Peel, a senior medical examiner, published an article in the 1997 British Medical Journal, where he cited several cases of people surviving between 28-40 days without food. My brother tried this experiment in his youth and was almost unrecognizable at the end of the 40 days. He was healthier after the fast.
These starvation diets could potentially be beneficial to the brain. According to an article in Nature magazine, when gherlin entered the hippocampus area of the brain of rodents, it altered nerve-cell connections and enhanced learning and memory. This would be good news for Humphrey because his brain would be better prepared to recall the mistakes he makes in his self-rescue efforts and to use these to his benefit. Humphrey will also need less sleep due to the extra gherlin in his system. This effect on human beings was reported in the PLoS medical journal. So, being hungry will actually be helpful to Humphrey in finding his way back out to civilization.
This dance of equilibrium between gherlin and leptin has taken on center stage in many studies of hunger, obesity, and disease. Studies have revealed an imbalance of these hormones in the bodies of people who are unable to maintain a healthy weight. The cause for the imbalance seems to have some genetic component and some environmental ones. There are no simple answers and, to complicate matters, there are many other chemicals that also play a role in hunger management. The variables to be understood are complex.
The ability to control these hormones promises a gold rush into the multi-billion dollar diet industry. In the medical arena, the capability to manage these hormones could also lead to control over obesity related diseases like diabetes, hypertension, high-blood pressure, etc. There are currently some medical procedures which reduce stomach size and thus reduce the production of gherlin. There have also been some studies which equate the level of leptin with obesity. Like many matters of the brain, there is quite a lot that is known and a lot that is still unknown. This makes it difficult to develop simple solutions.
This balancing trick is not special to humans. Other animals also have a hypothalamus. This organ resides in the limbic system which is also known as the reptilian brain. That is, we share this structure with some of the simplest creatures in the world. Similar to us, their brain also evolved to produce hormones to control the body so that it can feed itself and obtain the requisite energy for survival.
Of course, in unusual situations like that of Humphrey, there is no competition. There is only gherlin and it wants satisfaction. Unlike other animals, however, Humphrey can use other parts of his brain to manage the demands that the gherlin is exacting on his hypothalamus. He can distract his mind by thinking about something else. Simply being afraid can also distract as his mind also tries to deal with that challenge. Fear stimulates his sympathetic nervous system, increases adrenaline secretion and decreases appetite.
Once Humphrey finds his way out of the forest and eats food, his gherlin level will start to decline and his leptin level will start to rise. The amount of balance between the hormones will depend partly on his genetic structure and partly on his food lifestyle. In this particular case, it is possible that the emotional starvation caused by loneliness and fear, will also cause him to eat more than necessary. This type of emotional eating is a complex human behavior and requires looking beyond the interactions of just the hunger and satiety hormones. But, that is another story.
Please send feedback and suggestions for future columns to firstname.lastname@example.org. Links to past columns are available at WhoseBrainIsIt.com and Leena’s writing portfolio is available at FishRidingABike.com. Leena has a journalism degree from Stanford University.
Dr. Nicola Wolfe is a neuroscience consultant for this column. She earned her Ph.D. in Clinical Psychopharmacology from Harvard University and has taught neuroscience courses for over 20 years at various universities.
References for this article: Dr. Wolfe’s Neuroscience class at Berkeley extension, plonsone.org, Nature magazine.