Introduction
Our eating habits are formed as a result of a complex interplay between physiological states, memories, attitudes, and cultural norms. It makes therefore sense, that food behavior can be modulated via different mechanisms. And while there are many different perspectives and viewpoints from which we can observe food-related behavior, we can convey and gain a lot in our understanding, by looking at the neuronal activity related to eating. For that reason, we will look at the most responsible and active brain regions, when we observe and modulate eating behavior through multiple blog posts. From this viewpoint, we will try to rationalize, what a particular brain activity denotes and which aspect of our food-related activity it modulates. As we will see, the interplay and connectivity are vast which makes understanding and changing food behavior a challenging topic.
Finding the hunger-satiety brain region
Food behavior has been studied for thousands of years. But since neurosurgery and brain imaging techniques are a recent phenomenon, understanding eating behavior through brain regions is a recent research field as well.
Naturally, ingested food is transported through our digestive tract. And since the brain organizes and modulates those underlying peripheral units, a change of brain activity should be noticeable when food is ingested. All of these units modulate our perception and feeling of hunger, but their strong connection to different brain regions implies that modulation can arise bottom-up as well as top-down [1].
Initially, brain research showcased a dominant involvement of the hypothalamus, which was spotted to be highly active in patients with hyperphagia and later denoted hypothalamic obesity [2]. And while the involvement of the hypothalamus is highly profound, especially in animals with simpler brain structures, it was quickly established that complex beings (like mammals) are able to modulate and perceive food-related signals with higher-order brain structures. Those structures can form emotional states, attitudes, and habits that in a given moment establish a motivational valence towards a perceived (in the real world or cognitively imagined) food item.
The essence of understanding food-related behavior
As was discussed previously, many brain regions are involved in the processing and modulation of food-related behavior. Coming from sensing internal states of hunger and satiety with the more low-level structures such as the hypothalamus, to higher-order units, such as the insular cortex and prefrontal areas which denote emotional and cognitive aspects. This means that food behavior is not only motivated by specific hunger states, but also through imagination, current emotion, and previous experiences. When these structures elicit some association to the perceived food object, they evoke a cascade of signals, that should initiate an appropriate (motoric) response. From the response initiation, one needs to test if the approach (or move away) resolved the desire or need. In positive scenarios (when we like what we perceive), we are motivated to approach the perceived food item and we aim to eat it.
If the feedback from our sensory system and digestive tract is as expected, positive reinforcement will solidify our experience and make it more likely, that we will approach similar food items in similar future circumstances. Of course, there is also an interplay and competition between the associations formed in other brain structures involved i.e. some brain structures have positive associations while others have negative. Combined with our current state of the physiological need for specific nutrients, the motivation can be modulated, to even form an aversion toward the food item. For instance, someone being nutrient-deprived and having a physiological desire to eat, but can block that by having some higher-order belief or attitude towards eating the specific item or eating on that occasion.
Conclusions
In this blog post, we have provided an introduction to the topic of food perception as it happens inside our body. Here we the most important fact, that brain structures and our digestive tract are interconnected and form an interconnected net of association that provides feedback and modulates behavior. Especially when we look at the brain structures in higher-order mammals, we see a strong involvement in areas outside the hypothalamus, which is primarily responsible for sensing our physiological state of nutrient and energy availability.