How chemicals control your thoughts and feelings?

If you imagine yourself eating something tasty you'll probably start salivating and develop a desire to find that particular food. This happens to me almost every day with regard to chocolate. I was therefore excited to read a recent study that was published in the prestigious journal Science that tried to determine whether the simple mental exercise of imagining yourself eating a specific food, for example cheese, could habituate your need to actually eat the cheese when it became available. The scientists, lead by Carey Morewedge at Carnegie Mellon University, devised a series of clever ways to investigate the role of imagination in the the complex brain processes that control eating.

You are, of course, aware of what happens to your emotions when you imagine something frightening or just thinking about what it would feel like to have a large spider crawling up your leg right now as you read this sentence. Your heart begins to race and you start breathing a little faster until you confirm that nothing is actually crawling up your leg. However, if you kept tossing this scary image around in your mind over and over again, you will calm down and your heart rate and respiration will return to normal. This neural process is called habituation. Habituation is a decreased physiological or behavioral response to a repeated stimulus, e.g. thinking about that spider on your leg. Habituation works with regard to food as well. That first bite of chocolate is always the best; then as you continue to eat more and more the pleasure of eating it lessens and you lose interest in eating any more. Neuroscientists have now discovered the location in your brain where this process is handled. Your brain allows you to habituate to almost any sensory stimulus, including spiders, chocolate, awful odors, bright lights and loud noises.

Can just thinking about eating something, such as another piece of cheese or chocolate, habituate you to it and thus induce you to eat less? The answer is yes. The key discovery is that imagining the precise experience, such as individual pieces of cheese, over and over again was able to induce habituation. The subjects in this study consumed less of the specific food after mentally simulating the experience in their mind. Why did this work so well? Habituation is specific to only one stimulus at a time. If you habituate to one type of food, for example a cube of cheese, then you will consume less of that particular food without affecting the consumption of other types of food. Voila - you eat less cheese but are able to induce in chocolate!

Another amazing aspect of this study was that the subjects reported a decreased desire for eating the cheese but did not change their subjective feelings about how much they still liked cheese. The effect was enhanced by how much the subject thought about eating one particular food item. The subjects who imagined eating more of the food were ultimately less motivated to eat it when it became available, in contrast to subjects who thought less about consuming the food item. So get started immediately thinking about that food item you would like to avoid!

This study demonstrates some important lessons about the power of our imagination over the control of your diet and those midnight cravings for fries or ice cream. Neuroscientists and psychologists have documented various aspects of this mental control in many different ways; most of us know it simply as the placebo effect. In the future, as we continue to investigate the human mind, the line between actual experience and our mental imagery of that experience will likely become ever more blurry.