Analyses of gustatory related neural responses detected by brain magnetic fields

Recent studies on non-invasive recordings from human brain have shown the existence of tasteelicited activation areas in the cerebral cortex [1,2]. Magnetoencephalogram (MEG) is a popular instrument for these non-invasive measurement as well as functional MRI (f-MRI) and positron CT (PET). The advantage of MEG measurement is easy to analyze a time-course data as a function of taste-elicited information processing in brain, compare with f-MRI or PET study. In the following study, we tried to detect the stimulus latency of brain magnetic field evoked by different tastants which have different peripheral mechanisms, also have different latency in taste cell by animal electrophysiological approaches [3]. In addition, to confirm the primary latencies of tasteelicited activation in human brain, we used tastemodifying substance, which is contained in miracle fruit. Miracle fruit has a property of changing sour taste of acids to sweet taste. Using taste-modifying substance, we can confirm the differences of latencies by same taste stimulant. We improved the system of taste stimulation. The stimulus onset and the intensity of taste stimulants are important for a detection of evoked brain magnetic fields. We utilized a special mouthpiece for continuous-flow taste stimulation system. This mouthpiece can stimulate wider area of human tongue than previous system [4]. As for the analysis of source estimation, the equivalent current dipole method was utilized in this study. We report the method for taste-elicited MEG measurements would be very useful on study of gustatory information processing in human brain.