Distracted Taste: Neural Correlates of Gustatory Processing during Cognitive Distraction

Do we spend half our lives in front of screens? According to a recent survey in Germany, almost every second person agrees that they spend at least half of their day in front of a screen (Statista Consumer Insights, 2023). This modern lifestyle demands performing multiple tasks simultaneously and may favor an increased use of electronic devices while eating (e.g. reading, replying to emails or watching TV). Several studies established that the amount of food eaten increased when people watched TV while eating (Bellisle, Dalix, & Slama, 2004; Braude and Stevenson, 2014; Ogden et al., 2013). Braude and Stevenson (2014) further examined this phenomenon and showed that an increase of food intake was related to changes in sensory-specific satiety. Eating when distracted may lead to a higher amount of food necessary to achieve satiety. Remarkably, the amount of additional consumed food was equivalent to one extra meal per day. Stroebele and de Castro (2004) highlighted that this effect seems to be more pronounced in individuals who made eating in front of the TV a habit. This suggests an unfavorable long-term effect of distraction on our eating behavior. Similar effects have been observed in preschool children, with regular distracted eating contributing to increased body weight (Francis and Birch, 2006; Cox et al., 2012). However, despite these findings, the neurocognitive mechanisms behind “distracted” eating remain elusive. To date, no study has systematically investigated how distraction or cognitive load may affect gustatory perception and processing in the brain. However, there are relevant findings from research on olfactory perception under cognitive load. A study conducted at the former lab of Jessica Freiherr at Uniklinik RWTH Aachen focused on the influence of cognitive load on olfactory perception and processing using functional neuroimaging (Hoffmann-Hensel, Sijben, Rodriguez-Raecke, and Freiherr, 2017). It was established that odor intensity perception was diminished when the subject was performing a task with high cognitive load and that activity was lower in the piriform cortex and the orbitofrontal cortex, typical olfactory processing areas responsible for the diminished odor intensity evaluation. This might indirectly lead to overeating, through a mechanism that then compensates for the decrease in the strength of the olfactory signals. The brain imaging data revealed that the phenomenon of a lower odor intensity perception under high cognitive load was related to lower activation of the piriform and the orbitofrontal cortices and unrelated to the insula activation. It would be particularly interesting to find out whether a similar neural phenomenon applies to taste processing, namely that activation of brain areas involved in gustatory processing show less activation under distraction. With regards to the influence of body weight on taste perception, findings in obese individuals are inconclusive. Some studies have reported that obese subjects have higher taste sensitivity than lean subjects, especially for sucrose and salt (Pasquet, Frelut, Simmen, Hladik, and Monneuse, 2007), while others have shown decreased sensitivity to sweet and salty taste (Noel, Cassano, and Dando, 2017) or no differences at all (Martinez-Cordero, Malacara-Hernandez, and Martinez-Cordero, 2015). Neuroimaging findings suggest that obese subjects, in comparison to lean subjects, show stronger activation in various cortical (anterior cingulate cortex, insular and opercular cortices, orbitofrontal cortex) and subcortical (amygdala, nucleus accumbens, putamen and pallidum) structures involved in reward and food processing (Szalay et al., 2012). By means of EEG, it was shown that taste representations lived shorter and demonstrated a reduced strength in the obese, compared to the lean group (Hardikar, Wallroth, Villringer, and Ohla, 2018). Building on the abovementioned findings it is only reasonable to assume differences on behavioral as well as neural levels in gustatory processing under distraction depending on body weight. However, there have been no studies investigating the effects of cognitive load on taste perception including body weight until now. A recent behavioral study investigated the effects of cognitive distraction on gustatory perception (Ruda et al., 2024). Lean and overweight/obese participants played a Tetris game to induce low or high cognitive load, depending on the speed of falling blocks. While playing Tetris, gustatory stimuli (bitter, salty, sweet, umami, and a complex mango flavor) were delivered by a computer-controlled gustometer and the participants were asked to rate their intensity and the pleasantness on a 100-point visual analogue scale. We found that the perceived intensity and pleasantness of taste stimuli were reduced by cognitive distraction, with more pronounced effects in the overweight/obese group. Furthermore, gender and body weight seem to have an impact on gustatory perception. Taste sensitivity was positively correlated with BMI, especially in male participants, while females generally rated taste stimuli more intense. This behavioral study provided first insights into taste perception differences under distraction, but also raised questions that we want to address in our follow-up study: What are the underlying neural mechanisms of taste processing on a brain level that explain the behavioral effects of distraction on gustatory perception? Does this mechanism differ in effect or structure depending on body weight? If we know the underlying neural changes of “distracted eating” that may favor overeating and weight gain, can we establish an effective and widespread prevention for the general population to tackle these effects?