Psychophysical Measurement Of Taste Intensity And A Resting-state FMRI Study

The sense of taste plays a substantial role in our daily life,helping us to detect potential nutrients and stay healthy.The gustation is suggested to be divided into three dimensions: quality,intensity,affective value or pleasantness.Most researchers agree that there are five major categories of taste quality – sweet,sour,salty,bitter,and savory – each turned to identify a specific nutrient or poison and each associated with particular physiological functions.Stimulus detection is the most fundamental perceptual process.Gustatory detection thresholds measure the minimum amount of substance which is required to be present in solution in order to detect its presence at above-chance levels.And toxicity is a better predictor of central neural response than physical structure.The general Labelled Magnitude Scale(LMS)is applied to measure the intensity of taste stimuli.The peripheral nervous pathways of taste start at the taste buds in our tongue,where the dissolved composition of food is captured and some chemical reactions happen.Thanks to the chemical reactions,the characteristics of the food are codes as neural signals,which is the information transferred in our neural system.The food information is then carried through the cranial nerves ascending to the thalamus,and thalamic projections terminate in several regions of the insula and overlying operculum(AI/FO),as well as some other parts of cortex that involved in taste pathways,such as the amygdala.Many experiments have demonstrated that the AI/FO is the primary taste cortex,and insula is responsible for coding taste intensity.Sensations such as gustation,olfaction and visceral sensation may interact with taste intensity.The precise integration part,however,remains disputed.The neural representation of taste intensity is subtly modulated by up-down factors,such as selective attention and expectation.Taste perception varies among people with different age and different BMI.Neural processing in the amygdala may also contribute to intensity coding.Increases in taste intensity perception have been observed following unilateral resection from the anterior medial temporal lobe(with amygdala)for the treatment of epilepsy,and decreased taste intensity perception on the side of the tongue ipsilateral to an insular lesion.One possible explanation for this result is that a release from inhibition occurred.Similar observations have been reported following damage of the cortex of taste in humans,suggesting that inhibition may be a general property of the gustatory system.We assume that there is observed functional connectivity between amygdala and insula,and amygdala works by transport inhibition signal to insula,which is the primary taste cortex and represents taste intensity.The following studiesin this paper focus on the measurement of taste intensity of Chinese college students with taste stimuli of different qualities and different intensity.We also collect the Resting-State f MRI data to look for the possible activity of taste intensity responsible areas and the possible functional connectivity between brain areas.Our first study is the measurement of taste intensity.We recruited 27 college students to participant in this study.Four taste qualities(sweet,sour,salty and bitter)and three kind of intensity were used as the taste stimuli.In the study,all the participants finished two scales of “Body Perception Questionnaire”,which were“Awareness Questionnaire” and “Autonomic Nervous System Reactivity”.We also measure their BMI,which were used in the data analyze procedure.Results showed that there is consistency between the taste perception and stimuli intensity;there is significant correlation between the liking score and wanting score;there is significant difference among the taste intensity of three kinds of stimuli in each kind of taste quality;there is significant preference difference among four taste qualities,showing a preference for sweet stimuli and averseness for sour and bitter;there is significant correlation of taste intensity among taste qualities-sweet,sour and salty;there is no significant correlation between sour/salty and bitter;there is significant negative correlation between the Awareness Questionnaire score and taste intensity to high intensity of sweet stimuli and low intensity of sour stimuli;BMI shows no significant correlation with taste intensity.Second,we analyzed Resting-State f MRI data from 25 participants in study one.The Re Ho and possible functional connectivity were calculated.The result shows that the right anterior insula shows significant correlation with individual sensitivity of taste intensity.And no functional connectivity was found to correlation with taste intensity.These findings advanced our understanding to “what is taste intensity” and “how to measure it.It may establish foundation to reveal the complex neuromechanism of gustation.