By Emilie Reas, PLOS Neuroscience Community Editor
In today’s burgeoning wine industry, winemakers are in constant search of ways to perfect their product and achieve an edge over the competition. Complicating the challenge of producing a bottle that we’re sure to select at our next fine dining experience is the variability across palates. The individuality and unpredictability of sensory experiences – which may further be manipulated by context or expectations – make predicting a wine’s appeal a daunting task. In a dream world, winemakers could peer directly into the brain to examine the biological response to a smoky syrah or a spicy zinfandel. Such a tool could theoretically empower producers to target their wine characteristics to not just the psychological, but also the physiological response to a wine. In their study recently published in PLOS ONE, Frost and colleagues sought to accomplish just this, using functional MRI to assess brain responses to a wine’s flavor attributes.
Rather than assess relatively subjective features like fruitiness, tannins or fullness, the researchers focused on alcohol content, a more objective – and therefore easier to quantify – property. Twenty-one “inexperienced” wine drinkers (they imbibed less than once per week) participated in four wine-tasting sessions while undergoing functional MRI. During each session, they alternated among sipping a tasteless solution, a low-alcohol red wine (13-13.5%) and a high-alcohol red wine (14.5-15%). A different pair of low- and high-alcohol wines, matched on flavor, was tasted in each session. A post-scan taste-test confirmed that participants could not tell the difference between the low- and high-alcohol wines of each pair, as they rated their tastes as essentially identical.
Frost and colleagues identified 30 brain regions of interest that were activated by drinking wine, regardless of alcohol content. This set of areas was then further tested for effects of alcohol. Of these regions, only the right insula and right cerebellum were differentially activated by alcohol level, demonstrating greater activity to the low- than high-alcohol wines. Surprisingly, no regions preferentially activated to more alcoholic wines.
The cerebellum is known to be involved in sensorimotor processing, which could reasonably account for its activation by subtle differences in alcohol perception. However, both the insula and cerebellum have been shown to be modulated by taste, activating to more intense flavors and feelings of satiety. Shouldn’t high-alcohol wines – which are arguably more intense– therefore more heavily engage these regions? The authors dug deeper into the literature to interpret these unexpected findings.
They propose that because these areas are involved in “cognitive modulation of sensory perception” and “coordinating the acquisition of sensory information,” the lower alcohol wines might have “induced a greater attentional orienting and exploration of the sensory attributes.”
Yet there’s one tiny hole in this explanation, at least when considering the current evidence alone. We could reasonably link activation of these regions to flavor intensity or taste perception if there were some associated behavioral indication that the wines elicit distinct sensory experiences. However, the participants in fact report no perceptible taste difference between the two classes of wines. This discrepancy between the subjective perceptual experiences and brain responses suggests that the observed insular and cerebellar effects may reflect some sensory aspect of wine-tasting that lies below conscious awareness.
Although the researchers don’t directly discuss this possibility, it’s worth exploring. Since the difference in alcohol content between the wine types was notably small (just ~1.5%), it’s not surprising that the participants couldn’t detect a taste difference. It would be interesting to see whether the activations would be more robust to a wider gap in alcohol levels, or might track with a continuum of alcohol content. Furthermore, the study participants were “inexperienced” wine drinkers. Perhaps the taste differences would have been perceptible – or the brain responses stronger – in a sample of connoisseurs with more “refined palates.” As the evidence stands, we can’t conclude whether the BOLD responses indeed reflect effects of wine taste perception that were simply too subtle and hence immeasurable here, or instead relate to lower-level, unconscious sensory processes.
So what do these findings mean for the winemaker looking to neuroscience for a marketing advantage? It’s safe to assume that manipulating the alcohol content of a wine will indeed affect brain physiology (in fact, the known influence of alcohol on the BOLD signal raises concern over confounds between the wine conditions). However, it’s unclear how this brain response relates to a wine drinker’s sensory experience, let alone preference for one wine over another.
As blogger Neuroskeptic points out in his recent commentary on the study, “it’s not clear whether a brain scan is the best way to approach the question of whether high alcohol is overpowering. Surely the same thing could be demonstrated using a taste test.”
Despite these considerations, Frost and colleagues establish a solid stepping-stone to further explore the complex relationship between a wine’s flavor profile and consumers’ gustatory and neural responses. More importantly for wine-lovers everywhere, their study offers a key first step towards unraveling how and why that bold, oaky cabernet beats a merlot any day.
Any views expressed are those of the author, and do not necessarily reflect those of PLOS.
Bower JM et al. (1981). Principles of Organization of a Cerebro-Cerebellar Circuit. Brain Behav Evol 18:1-18. doi:10.1159/000121772
Frost R et al. (2015). What Can the Brain Teach Us about Winemaking? An fMRI Study of Alcohol Level Preferences. PLOS ONE. doi: 10.1371/journal.pone.0119220
Plassmann H et al. (2008). Marketing actions can modulate neural representations of experienced pleasantness. Proc Natl Acad Sci 105(3):1050-4. doi:10.1073/pnas.0706929105
Small DM et al. (2003). Dissociation of Neural Representation of Intensity and Affective Valuation in Human Gustation. Neuron 39(4):701-11. doi:10.1016/S0896-6273(03)00467-7
Smeets PAM et al. (2006). Effect of satiety on brain activation during chocolate tasting in men and women. Am J Clin Nutr 83(6):1297-1305.
Emilie Reas received her PhD in Neuroscience from UC San Diego, where she used fMRI to study memory. As a postdoc at UCSD, she currently studies how the brain changes with aging and disease. In addition to her tweets for @PLOSNeuro she is @etreas.