Discrimination of Concentration of Salt in Solution in Human Brain

Objectives: The aim of this study was to investigate which part of human brain activates for discriminating the taste intensity of salty solutions.
Methods: The study was carried out in 34 healthy volunteers: 17 females and 17 males (18 – 27 years). Functional magnetic resonance image (MRI) was performed and brain functional data was acquired while participant tasted three concentrations of sodium chloride (NaCl) solutions (1 mM, 300 mM, and 500 mM). The NaCl solution was delivered for 4 s and distilled water for 8 s alternately on the tongue using original intraoral device and taste delivery system. Image pre-processing and data analysis were performed using the Statistical Parametric Mapping 8 software package (Wellcome Trust Centre for Neuroimaging, London, UK) implemented in MATLAB R2012a (The MathWorks Inc., Natick, MA, USA). We conducted region-of-interest analysis at thalamus, insula and postcentral gyrus. We investigated the statistical parametric maps generated by each salty solution and by the differences between solutions at a threshold of p < 0.05, corrected for multiple comparisons using the family-wise error rate (FWE) (p_FWE).
Results: Functional MRI showed that brain regions activated by taste solution. For each solution, the 300 mM solution activated the postcentral gyrus (p_FWE < 0.005); activities in the insula and thalamus were observed (p_unc < 0.005). The 500 mM solution activated the insula significantly (p_FWE < 0.05) and the postcentral gyrus (p_FWE < 0.001); activity in the thalamus was seen (p_unc = 0.001). For differences in activation between solutions, 300 mM –1 mM activated the insula (p_unc < 0.001) and the postcentral gyrus significantly (p_FWE < 0.05). For 500 mM –1 mM significantly activated the insula (p_FWE = 0.005) and postcentral gyrus (p_FWE = 0.001).
Conclusions: Insula and postcentral gyrus in human brain activated for discriminating the taste intensity of salty solutions.