This week's article for my blog is by Gorica D. Petrovich, and it is called "Learning and the motivation to eat: Forebrain circuitry." As the name suggests, some biology will be brought up, as I attempt to connect it to psychological principles and different learning mechanisms and eating habits that I have learned about and blogged about for the past couple of months. Two important topics I will hit upon in this blog are the ideas about cues that cause a subject to eat while sated and fear/anxiety inducing cues that can inhibit eating, even in states of hunger.
This article hits upon multiple different points related to learning/motivation and eating, and as I discuss them they will be a good review of some of the topics I have previously discussed. One of the topics talked about is the environment in which food is consumed. There are always cues associated with certain foods, and the environments in which we sit down to eat, that serve as conditioned stimuli (CS) and trigger our urges to eat, even if we are not particularly hungry. I have talked about this in a previous blog, and I have discussed the importance of trying to limit those cues. I suggest that, the next time you plan on eating lunch or dinner, eat it in a novel environment, so you don't end up showing a conditioned response to the environment and then overeat... you will be able to limit yourself more effectively. If you, as I do, normally eat at the kitchen table, then switch to the dining room or to the living room, so that you don't trigger those usual cues. For example, my kitchen table is right next to the pantry, and after I finish my meal, I usually go digging around there to see what cookies or desserts we have lying around. It has become a habitual behavior, where sometimes I take the few steps over to the pantry with my eyes still glued to the TV and I don't even realize how automatic the behavior has become. It is also important to develop new preferences and reminders for "healthy" foods. One suggestion I have is that you create a vegetable tray at home of different vegetables that you enjoy eating and place that at eye level of your refrigerator... this way you will associate the cue of walking to your refrigerator and opening the door with the vegetables that you are about to consume. In other words, the cue will serve as a constant reminder of the healthy food reward, rather than having high-calorie foods such as cakes in your immediate vicinity and placed at eye-level. Put the cakes further back in the refrigerator or on a different level, just so that you don't see the box from "Gelson's" or "Sprinkle's Cupcakes" and remind yourself of how that high-calorie red-velvet cake is going to taste (these boxes from Gelson's or wherever else are the type of environmental cues we should watch out for and distract ourselves from).
The researchers of the study decided to lesion different parts of the rat brains to see how they affected eating. One discovery they made was that rats with a lesion of the ventromedial prefrontal cortex (vmPFC) ate less food than controls when fed in a novel environment, or when novel food was first presented in a familiar environment. Since the rats in these studies did not have a change in body weight, it suggests that the vmPFC is not responsible for homeostatic control of food intake and body weight, but instead may be important for judging environmental signals and prior experience. Just make sure you don't jump to any rash conclusions with a study like this, as lesion studies are just meant to be informative and responsible for learning about how the different parts of the brain operate. This is, by no means, meant to be a solution to overeating as it would be impractical to go around chopping off slices of the brain of every person who ate too much.
The other major point I wanted to talk about in my blog is the idea of induced fear inhibiting eating. In the wild, this is an evolutionary adaptation because in the event that you are chased by a lion and you are running for your life, there is no time or desire to eat or search for food. During the fight-or-flight response, it is well known that our digestion slows down so that we can divert our energy to more important functions. Rats that receive tone-shock pairings eat a lot less food than rats in a control condition as this article points out. When rats are frightened, their natural response is to freeze. This is because they are not particularly fast animals to run away from danger, so it is more beneficial for them to freeze and try to blend in with their background by not moving, or at least give the appearance that they are dead, with an extremely slow heart rate. Certain experiments referred to in this article talk about the fact that both freezing and inhibition of feeding are indued by the same conditioned stimuli, in other words, the same CS triggers both responses in rats. This is proven by the work of brain lesions of the ventrolateral region of the periaqueductal gray that were able to stop conditioned freezing, but left inhibition of eating intact. Conditioned freezing and inhibition of eating are both part of a motivational system that is important for defensive behavior. Before we jump to any conclusions about their use in overeating, let's remember that prolonged fear is associated with anxiety, and is more likely to result in maladaptive behaviors and disordered eating such as Anorexia nervosa. Very little is known, as of now about the brain circuitry through which fear and anxiety inhibit feeding, so it will be a while until we can lesion out the correct regions.
It may sound far-stretched to say that we should induce fear in people who are trying to lose weight or who are morbidly obese and need to stop overeating, but there are examples of this in real life that may signal otherwise (as long as it is not prolonged fear). Based on an example from my own life, my mother, in some ways, is a fear-inducing cue in my household because of the way she criticizes or gets mad at someone for eating junk food and not eating enough healthy foods. I don't mean, in any way, to make my mom sound like a bad person, but this is the best example that i could think of, which also seems to be pretty accurate. I have come to learn that, in her presence, I can not eat any junk food, I should not be overeating, and I should pull out the vegetable tray if I want to munch on a snack, instead of eating pita chips or candy. Although the prototypical example is the struggle for survival in the wild which inhibits hunger or the fear of a shock inhibiting hunger in mice, my example runs along the same principles. When my mother is in the house and is looking to watch what we eat, I feel myself shift my focus and either stop eating altogether or eat something healthier. I know that she does it for our own good and in many ways this approach has been working because I am eating healthier more often, especially at home. You may not assume that this type of training transfers over to other settings, much like extinction in a therapist's office does not always transfer to the real world, but surprisingly, it is generalizing, and is converting my overall eating behavior. Sometimes that's just the way things happen.
Although there are some advancements being made in the field of brain lesions and figuring out how we can regulate our eating, fear behaviors, etc. we are still a while away from figuring out how fear and anxiety inhibit feeding. I have made some suggestions in this blog about how to change the environment that you eat in, and to adjust the cues that would trigger you to eat. If those do not work out for you, then you can always have someone shock you or scare you every time you are about to overeat, just as long as the fear does not last for too long!
Stay tuned for my final blog next week as I recap many of the topics I have covered and discuss some of the most important lessons I have learned over these 10 weeks!
References:
Petrovich, G.D. (2011, April 28). Learning and the motivation to eat: Forebrain circuitry.
Elsevier, (104), 582-589. Retrieved from http://www.sciencedirect.com/science/article/
pii/S0031938411002186
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