On every street in Paris, there are three things you are certain to find: a boulangerie (or two or three), some sort of bistro/brasserie/café, and a Franprix (my personal favorite, a small-scale grocery store). Clearly, cuisine is central to Parisian life. And often, the options boil down to baguettes, wine, and cheese.
a typical boulangerie (“Savouries Counter – La Renaissance Patisserie” by avlxyz is licensed under CC BY-SA 2.0)
As a lover of spicy foods, I was at a bit of a loss. After about a week into my stay in Paris, I was ready to reintroduce some of the essential components of my normal diet—mainly, I’m referring to chili paste and other spices. Perusing the Franprix directly below my apartment, I was shocked to see that there was only one option for hot sauce. Not only this, but every café and restaurant I had been to showed no promise of the tongue-scorching, eye-watering foods I love. So I had some questions: why do I enjoy spicy foods so much? How are they registered in my brain? Is there a certain part of my brain—specifically for processing spicy taste sensations–that is more active for me than for a French person?
my chili paste from Franprix (Personal Image)
Before attempting to tackle any of these questions, let’s first explore how our brains perceive sensory information from the world around us.
The five basic senses–sight, sound, smell, taste, and touch–all have particular areas of the brain (in the bumpy outer layer called the cortex) devoted to receiving signals from our eyes, ears, nose, mouth, and skin, respectively. The area of the brain that registers taste is called the gustatory cortex.
Basic taste perception (Image from Frontiers for Young Minds)
Nestled in taste buds scattered about the surface of the tongue, special receptor cells interpret chemical stimuli as sweet, salty, bitter, sour, and umami. From there, signals are sent to sensory neurons and into the brain through cranial nerves (Breslin and Spector, 2008). Spicy foods are detected a bit differently than other tastes, since these signals involve pain receptors (Immke and Gavva, 2006). But, recent neuroscience research has been determined that these signals still activate the gustatory cortex, so they count as a legitimate tastes (Rudenga et al., 2010)! Therefore, it seems that French cuisine is indeed missing an entire taste sensation, and it happens to be the one that is my favorite.
Taste bud (Image from LumenLearning.com)
Now that we’ve legitimized these piquant flavor sensations, let’s dive deeper into the neuroscience behind them.
While scientists still don’t understand exactly how taste perception works, it is clear that capsaicin (the chemical responsible for the spicy qualities of many of my favorite foods) actually results in unique brain responses. Unlike the other tastes, spicy sensations are often accompanied by the release of endorphins (explaining how they can be perceived as pleasurable) and activation of the autonomic nervous system. This unconscious system of bodily regulation is responsible for the perspiration, higher body temperature, and a faster heart rate associated with “hot” foods (McCorry, 2007).
In a 2015 study entitled “The Brain Mechanisms Underlying the Perception of the Pungent Taste of Capsaicin and the Subsequent Autonomic Responses,” Kawakami et al. (2015) investigated how these bodily responses happen after someone eats spicy food. The authors knew that the gustatory cortex (consisting of the middle and posterior short gyri, or M/PSG, of the insular cortex) must somehow be in communication with the brain area controlling autonomic system responses (the anterior gyrus of the insular cortex, or ASG). But, it wasn’t clear how this communication was happening.
In order to test this, the researchers administered three different taste solutions (spicy, salty, and neutral) to twenty human study participants. As the subjects tasted the solutions, the researchers took a look at their brain activity.
The method they used to analyze brain activity is called functional magnetic resonance imaging (fMRI). This produces high-resolution images of the brain while it is in action. Blood oxygenation level-dependent (BOLD) signals show where oxygenated blood is being used, indicating which regions are using up the most resources (Logothetis, 2003).
The ASG and M/PSG (Image from Frontiers in Human Neuroscience journal, Kawakami et al., 2015)
After performing this test, the researchers compared the brain images from the subjects. Their main findings were that there was coordination between the activity of the M/PSG and the ASG when people eat spicy foods. This could mean that these two brain areas are syncing up in order to produce symptoms like sweating and a quickened heartbeat after spicy food is consumed. Moreover, these results support the findings of another study done with mice, which concluded that cells in the ASG and M/PSG synchronize their activity patterns when capsaicin is tasted (Saito et al., 2012).
Kawakami et al. (2015) also found that the ASG was even more active than the M/PSG in response to capsaicin. Not only that, but both brain regions were significantly more active in response to capsaicin compared to the other solutions!
In sum, this study and previous work has helped to explain how the brain registers the taste of “hot” foods in the gustatory cortex and coordinates it with autonomic nervous system activation. However, the researchers only tested three taste sensations, and clearly, there is still much to be discovered about how the neuroscience behind gustation. Future work will likely take a closer look at the connection between the ASG and the M/PSG, possibly providing more insight into why some people (like me) find these mildly painful sensations more enjoyable than others.
Baguettes are a staple in the Parisian diet (“Bag It” by Very Quiet is licensed under CC BY-SA 2.0)
In the meantime, perhaps knowing that eating spicy foods more fully engages the brain will inspire the French to literally “spice up” their diets and rethink that bland baguette, or at least offer more options in their grocery stores. That would make this hot sauce-lover very happy, and it would add a whole new dimension to French cuisine!
References:
Breslin, P.A., Spector, A.C. (2008). Mammalian taste perception. Current Biology. 18:R148-155. doi: 10.1016/j.cub.2007.12.017.
Immke, D.C., Gavva, N.R. (2006). The TRPV1 receptor and nociception. Seminars in Cell and Developmental Biology. 17:852-591. doi: 10.1016/j.semcdb.2006.09.004.
Kawakami, S., Sato, H., Sasaki, A.T., Tanabe, H.C., Yoshida, Y., Saito, M., Toyoda, H., Sadato, N., Kang, Y. (2015). The brain mechanisms underlying the perception of pungent taste of capsaicin and the subsequent autonomic response. Frontiers in Human Neuroscience. 9:720. doi: 10.3389/fnhum.2015.00720.
Logothetis, N.K. (2003). The underpinnings of the BOLD functional magnetic resonance imaging signal. Journal of Neuroscience. 23:3963-3971. doi: 10.1523/JNEUROSCI.23-10-03963.2003.
McCorry, L.K. (2007). Physiology of the Autonomic Nervous System. American Journal of Pharmaceutical Education. 71:78.
Rudenga K., Green B., Nachtigal D., Small D.M. (2010). Evidence for an integrated oral sensory module in the human anterior ventral insula. Chemical Senses. 35:693–703. doi: 10.1093/chemse/bjq068.
Saito, M., Toyoda, H., Kawakami, S., Sato, H., Bae, Y.C., Kang, Y. (2012) Capsaicin induces theta-band synchronization between gustatory and autonomic insular cortices. Journal of Neuroscience. 32:13470-13487. doi: 10.1523/JNEUROSCI.5906-11.2012.
Images (in order of appearance):
https://kids.frontiersin.org/article/10.3389/frym.2017.00033
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4717328/
Hyperlinked Videos/Sites:
https://www.youtube.com/watch?v=wGXoYippog8
https://neuroscientificallychallenged.com/blog/2013/05/what-is-insula
