Eidenberger, T. | bioRxiv Science

bioRxiv2025

Human Neural Synergy when combining Stevia with a Flavor Modifer and the Neural effects of Sucrose vs Stevia

There is a drive to improve the acceptability of sweeteners like stevia by reducing their off-tastes. The main aim was to examine the synergistic neural effects of combining stevia with a flavor modifier and secondly to examine stevia vs. sucrose due to limited human neuroimaging data and concerns that sweeteners may be more addictive than sugar. In a within-subjects fMRI study, 34 healthy adults (Mean age = 25) tasted four conditions: stevia, stevia plus a flavor modifier, the modifier alone, and sucrose. We analyzed whole-brain responses and focused on regions of interest (ROIs) including the insula, postcentral gyrus, and hypothalamus (identified via meta-analysis of sweet taste processing), as well as the nucleus accumbens (NAcc) and amygdala due to their roles in reward and aversion. Stevia combined with the modifier evoked super-additive responses in the postcentral gyrus, parietal cortex, and occipital gyrus (p < 0.05, FWE-corrected). Compared to stevia alone, the stevia-modifier combination elicited reduced hypothalamic activity (p = 0.008) and the hypothalamus tracked pleasantness and mouth fullness only in this condition. The NAcc tracked mouth fullness more for the modified stevia than for stevia alone, and the amygdala tracked bitterness only in the plain stevia condition. Sucrose elicited higher postcentral gyrus activation than stevia (p = 0.01). We provide first evidence that combining stevia with a flavour modifier reveals synergistic neural activity associated with taste sensation, intensity and multisensory integration. Adding a modifier to stevia could increase unconscious desirability for stevia by masking its bitterness and increasing its mouth fullness.

neuroscience↗

bioRxiv2025

Retro Nasal blockade reduces the Neural Processing of Sucrose in the Human Brain

It is assumed "Non-volatile" tastes like sucrose do not activate retro nasal pathways. Recent studies find that sucrose when aerosolized, can reach the retro nasal olfactory region and be perceived. The neural mechanisms by which the human brain interprets sucrose via retro nasal pathways is unknown. We examined neural activity to sucrose with a nose clip on (blocking retro nasal) and nose clip off, in healthy adults (N=34, mean 25 yrs.). We examined the whole brain and ROIs involved in taste, smell, attention, reward and multi-modal integration; insula, postcentral gyrus, amygdala, olfactory cortex, subgenual and pregenual anterior cingulate, nucleus accumbens and OFC. We also examined correlations with subjective ratings of pleasantness and mouth fullness. We also examined the effect of the nose clip on the time to peak activity for sucrose using the bold signal time course. The nose clip on vs off reduced the subjective experience of mouth fullness. Neural activity to sucrose was reduced with the nose clip on in the primary taste, olfactory, attention and reward ROIs and in the rolandic operculum, lingual gyrus and precuneus in the whole brain analyses. The olfactory and prefrontal cortex ROIs tracked subjective mouth fullness, but this was not apparent with the nose clip on. Blocking retro nasal sensation reduces subjective and neural responses to sucrose taste. Retro nasal sensations could play a role in "pure" taste perception. Developing more satisfying low-sugar foods could be achieved by enhancing the perception of sweetness through aroma modulation.

neuroscience↗