Linking psychophysical perception and prefrontal hemodynamics to characterize umami–spicy flavor interactions

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Umami–spicy combinations are widely used in food formulation, yet objective evidence explaining how spiciness modulates umami perception remains limited. Most previous studies have focused on the neural coding of single taste qualities, with limited attention to the mechanisms underlying flavor interactions. In particular, the prefrontal cortex (PFC) has been implicated in flavor integration and higher-order cognitive processing, but its role in umami–spicy interactions remains unclear. This study combined psychophysical perception with functional near-infrared spectroscopy (fNIRS) to investigate the neuro-sensory basis of capsaicin-modulated umami perception. Monosodium glutamate (MSG) solutions at low, medium, and high concentrations were evaluated with or without a fixed concentration of capsaicin. Sensory results showed that capsaicin enhanced perceived umami intensity and pleasantness at medium and high MSG concentrations, whereas no enhancement was observed at the low MSG concentration. fNIRS analysis revealed that umami–spicy stimulation at different concentrations significantly activated the orbitofrontal cortex (OFC), dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC), and frontopolar area (FPA), indicating coordinated involvement of these regions in the cognitive processing of umami–spicy perception. These findings provide new insight into how spiciness modulates the neural processing of umami in the human brain. They also offer a scientific basis for the development of food products with optimized umami–spicy sensory profiles.