Retro Nasal blockade reduces the Neural Processing of Sucrose in the Human Brain
Traditionally, taste perception is understood to occur through taste receptors located in the oral cavity, particularly on the tongue. Recent findings suggest that taste compounds, when aerosolized, can reach the retro nasal olfactory region and be perceived. However, the neural mechanisms by which the human brain interprets taste stimuli via retro nasal pathways remain unclear. Healthy adults (N=34, Mean age 25 yrs.) were recruited. We examined neural activity during the tasting of sucrose with a nose clip on (to block retro nasal sensation) compared to when there was no nose clip. We examined whole brain data and ROIs involved in taste (insula, postcentral gyrus, amygdala), smell (olfactory cortex, piriform cortex) odour attention (sgACC) and multi-modal flavour processing (OFC) and reward (pgACC and nucleus accumbens). We also examined subjective ratings of pleasantness and fullness of the sucrose with and without the nose clip. We found that the nose clip condition reduced neural activity in primary taste and olfaction regions and regions involved in attention to odours, and food reward. When examining the whole brain activity, we also found reduced activity in the rolandic operculum, lingual gyrus and precuneus. The olfactory cortex and prefrontal cortex ROIs tracked the sucrose subjective fullness ratings, but this effect was not present with the nose clip on. In conclusion, our findings are the first to demonstrate that blocking retro nasal sensation with a nose clip significantly reduces the subjective and objective neural responses to sucrose taste. These findings support the idea that retro nasal sensations could play a role in the perception of sucrose taste. This study suggests that developing more satisfying low-sugar foods could be achieved by enhancing the perception of sweetness through aroma modulation.