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A high-concentration NaCl solution does not stimulate the human trigeminal nerve at the tip of the tongue
Abstract
A 3 M NaCl solution does not stimulate the trigeminal nerve in the human tongue. Objectives. In rats, the trigeminal nerve has been reported to respond when the tongue is stimulated by a solution with an NaCl concentration of 0.4 M or greater. We have attempted to clarify whether or not relatively high concentrations of NaCl stimulate the trigeminal nerves of the human tongue.
We examined four patients whose bilateral chorda tympani nerves were resected during middle ear surgeries. We performed subjective tactile and taste tests. Next, we conducted objective examinations of the subjects' tactile and gustatory functions by magnetoencephalography (MEG).
The subjective examination confirmed that all four subjects maintained normal tactile sensory functions in their tongues and that the gustatory sensation at their lingual apexes was totally abolished. Furthermore, the objective examination of the tactile function using MEG indicated that their brain responses to trigeminal nerve stimulations were normal. Further examination using MEG failed to produce brain responses to a 3 M NaCl solution in spite of their normally functioning trigeminal nerves. Therefore, we concluded that a 3 M NaCl solution does not stimulate the trigeminal nerve at the tip of the human tongue.
... The facial nerve has different branches, the chorda tympani and the superficial petrosal nerve. The Chorda tympani nerve stimulates the inner tongue and conveys signals (Komiyama et al., 2007), while the superficial petrosal nerve actuates soft palates. The nucleus solitarius receives these signals from the pontomedullary junction in the brainstem (Gibbons & Sadiq, 2019). ...
Males and females respond differently at the muscular level to various tastes and show varied responses when eating different foods. In this study, we used surface electromyography (sEMG) as a novel approach to examine gender differences in taste sensations. We collected sEMG data from 30 participants (15 males, 15 females) over various sessions for six taste states: a no-stimulation physiological state, sweet, sour, salty, bitter, and umami. We applied a Fast Fourier Transformation to the sEMG-filtered data and used a two-sample t-test algorithm to analyze and evaluate the resulting frequency spectrum. Our results showed that the female participants had more sEMG channels with low frequencies and fewer channels with high frequencies than the male participants during all taste states except the bitter taste sensation, meaning that for most sensations, the female participants had better tactile and fewer gustatory responses than the male participants. The female participants responded better to gustatory and tactile perceptions during bitter tasting because they had more channels throughout the frequency distribution. Moreover, the facial muscles of the female participants twitched with low frequencies, while the facial muscles of the male participants twitched with high frequencies for all taste states except the bitter sensation, for which the female facial muscles twitched throughout the range of the frequency distribution. This gender-dependent variation in sEMG frequency distribution provides new evidence of differentiated taste sensations between males and females.
... As shown in Fig. 2a, c, we presented the gustatory stimulus for a short duration in a small area on the tip of the participant's tongue. In a previous study (Komiyama et al. 2007), 300 mM saline was presented on the tip of the tongue in this manner and did not stimulate trigeminal nerve. ...
IntroductionIf odor and taste are presented in a context with high temporal proximity, they are more likely to be perceived as a flavor object. However, if odor and taste are presented in a context with low temporal proximity as well as a context with high temporal proximity, they may be less likely to be perceived as a flavor object. Based on these expectations, we hypothesized that sensitivity to temporal difference between two sensations (i.e., temporal resolution of synchrony perception) is higher when odor and taste are presented under a condition including a context with low temporal proximity than under a condition excluding it.Methods
To test this hypothesis, we required participants to determine whether olfactory and gustatory stimuli were presented simultaneously under a condition including a context with low temporal proximity (wide-range condition) and under a condition excluding it. In addition, we also tested visual–gustatory and olfactory–visual combinations.ResultsThe temporal resolution was significantly higher under the wide-range condition than under the narrow-range condition, supporting our hypothesis.Conclusion
For odor and taste to be perceived as flavor, people not only must experience high temporal proximity of the two sensations but also must not experience low temporal proximity of the two sensations.ImplicationThe findings of this study suggest that the higher the sensitivity to a temporal difference between odor and taste, the lower the robustness of a flavor object (i.e., the strength of the odor–taste connection).
... It is debated whether an increase in taste concentration can lead to concomitant activation of the oral somatosensory system via free nerve fibers innervating the tongue (Komiyama et al., 2007). While the latency of this activation appears rather fast, it reflects unlikely a purely lingual somatosensory response as this would occur much earlier at latencies of around 10-60 ms and more pronounced over the contralateral hemisphere. ...
Die sensorischen und hedonischen Eigenschaften von Essen sind wichtige Einflussfaktoren für die Nahrungsauswahl und –aufnahme. Was macht die Anziehungskraft von Nahrungsreizen aus? Die sensorischen und hedonsichen Eigenschaften von Nahrungsreizen werden mit allen Sinnen, oftmals sogar gleichzeitig, verarbeitet. Nahrungswahrnehmung ist damit ein mutlisensorisches Phänomen. Der Geruch, der Anblick, der Tasteindruck oder Geräusche können bereits vor der Nahrungsaufnahme wahrgenommen werden und Erwartungen hinsichtlich des Geschmacks auslösen. Diese prä-ingestiven Wahrnehmungseindrücke spielen daher auch eine maßgebliche Rolle bei der Entstehung von Verlangen und Gelüsten. Während der Nahrungsaufnahme, beim Kauen und Schlucken, spielen die chemischen Sinne, Schmecken und Riechen, eine besondere Rolle. Der Gesamtsinneseindruck aus den chemischen Sinneskanälen wird auch als Flavor bezeichnet. Wobei angemerkt sein soll, dass auch nicht-chemische Sinne, Sehen, Hören und Tasten, in die Flavordefinition einbezogen werden können. Zweifelsohne stellt die Nahrungsaufnahme ein komplexes Verhalten dar, das perzeptuelle, kognitive und Stoffwechselprozesse gleichermaßen umfasst. Die vorliegende Habilitationsschrift widmet sich der Untersuchung der neurokognitiven Mechanismen der visuellen, gustatorischen und flavour Wahrnehmung von Nahrungsobjekten und umfasst Untersuchungen zur Vulnerabilität der neuronalen Repräsentationen durch kontextuelle Reize. Zusammenfassend schließt die Arbeit mit der Feststellung, dass ein umfassendes Verständnis der psychophysiologischen Mechanismen der sensorischen und hedonischen Verarbeitung von Nahrungsreizen über alle Sinne die perzeptuelle Grundlage für nahrungsbezogenes Urteilen und Entscheiden darstellt.
... Taste stimulation was carried out using the same protocol as our previous study [3]. In brief, the tastant used was 1 M NaCl dissolved in deionized water that induces no somatosensory response through the trigeminal nervous system in humans [12]. Lying on their backs in the scanner, participants received a series of fluids on the dorsal surface of the tongue tip placed in a small pore (7 Â 2.8 mm) of a Teflon tube, through which deionized water and tastant were delivered from a revised version of a computer-controlled taste stimulator [1]. ...
... In support of the PGA's residence in the frontal operculum,Veldhuizen et al. (2007)ascribed the activation in the parietal operculum to activities in oral tactile afferents. On the other hand, in support of our MEG findings (Kobayakawa et al. 1996Kobayakawa et al. , 1999),Komiyama et al. (2007)found no activation by 3 M NaCl (aversive high concentration) in either the parietal operculum or the posterior insula in patients who had chorda tympani nerves bilaterally resected during middle ear surgeries. They also found that mechanical stimulation at the tip of the tongue evoked the shortest activations only at the oral cavity representation region in the central sulcus (probably its posterior wall), not at the parietal operculum. ...
The relationship between neuronal activity in the human gustatory cortex and the concentrations of taste stimuli is not well
understood. In this study, we recorded changes in the magnetic fields of the human brain in response to four concentrations
of NaCl (30 mM, 100 mM, 300 mM, and 1 M) and measured the magnitude and shortest latency of the equivalent current dipole
(ECD) in the primary gustatory area of the cerebral cortex (PGA). The average magnitude of ECDs in the PGA increased in a
concentration-dependent manner throughout the entire range of NaCl concentrations. The shortest latency of the ECD, however,
did not vary with the stimulus concentration.
... The glossopharyngeal nerve receives sensory inputs from the posterior tongue and is associated with both somatosensory tactile and gustatory sensations. The lingual nerve innervates the anterior part of the tongue where it performs somatosensory functions and the chorda tympani nerve innervates the anterior tongue where it is engaged in relaying gustatory information (Komiyama et al., 2007). ...
Magnetoencephalographic recordings were evaluated in five different states: normal condition, sweet, bitter, sour, and salt taste. Twenty-eight healthy volunteers, 14 male and 14 female, ranging from 12 to 50 years of age, were included in the study. The results showed that, in the normal condition, as well as in the sweet and the bitter taste, the male volunteers exhibited a higher count of low-frequency than high-frequency channels compared to the femal ones; in the case of the sour taste, there was no clear differentiation between the genders; with the salt taste, the female volunteers exhibited a higher count of low-frequency channels whereas there was no clear differentiation in the number of high frequencies between the gender. A discrimination in the spatial distribution of the frequencies provides novel insights into the identification of gender-related taste sensation.
... Taste stimulation was carried out using the same protocol as our previous study [3]. In brief, the tastant used was 1 M NaCl dissolved in deionized water that induces no somatosensory response through the trigeminal nervous system in humans [12]. Lying on their backs in the scanner, participants received a series of fluids on the dorsal surface of the tongue tip placed in a small pore (7 Â 2.8 mm) of a Teflon tube, through which deionized water and tastant were delivered from a revised version of a computer-controlled taste stimulator [1]. ...
In magnetoencephalogram studies, the primary gustatory area, area G, is not always seen in the same coronal plane in both hemispheres. We investigated possible asymmetry in right-handed and left-handed individuals by functional MRI. Group analyses revealed a significant difference in the antero-posterior coordinates of the area G between the right and left hemispheres in the right-handed group, but not in the left-handed group, indicating significant morphometric asymmetry in the former group and ambiguous morphometric asymmetry in the latter. However, in left-handed individuals with motor speech areas detected in the right hemisphere, area G was more posteriorly located in the right than in the left hemisphere. These findings suggest that the motor speech area contributes to the asymmetric location of area G.
Synopsis
Taste plays an undisputed role in the sensory analysis of food, and it ensures the identification of nutrients and harmful constituents. This chapter focuses on the perceptual basis of taste and its cortical representations in humans. Because taste seldomly occurs in isolation during eating and drinking, it has been considered to be inherently multisensory. To address this, an excursion is made to the confusion of taste and smell as well as to the role of visual food perception, which is a potent predictor of taste and food appreciation.
Functional magnetic resonance imaging (fMRI) was used for revealing activations in the human brain by lateralized tactile-gustatory stimulations of the tongue. Salt, a basic taste stimulus, and water, now recognized as an independent taste modality, were applied to eitherhemitongues with pads similar to the taste strips test for the clinical psychophysical evaluation of taste. With both stimuli, the observed cortical patterns of activations could be attributed to a combined somatosensory and gustatory stimulation of the tongue, with no significant differences between salt and water. Stimulation of each hemitongue evoked a bilateral activation of the anterior insula-frontal operculum, ascribable to the gustatory component of the stimulation, and a bilateral activation of the inferior part of the postcentral gyrus, ascribable to the tactile component of the stimulation. The results are in line with the notion that the representationof the tongue in the cerebral hemispheres in both the touch and the taste modalities is bilateral. Clinical and brain stimulation findings indicate that this bilaterality depends primarily on a partial crossing of the afferent pathways, perhaps with a predominance of the crossed pathway in the touch modality and the uncrossed pathway in the taste modality. Previous evidence suggests that the corpus callosum is not indispensible for this bilateral representation, but can contribute to it by interhemispheric transfer of information in both modalities.
Copyright © 2015. Published by Elsevier Inc.
We previously reported that cortical activities of the transition between the parietal operculum and the insula (area G) showed to increase in a concentration-dependent manner using stimuli containing 30 mM to 1 M NaCl. We investigated, in this study, the relationship between the magnitude of the activity with the shortest latency and the perceived gustatory stimulus intensity. We also examined the latencies at which activities correlated significantly with neural processes encoding perceived intensity and estimated the locations of the cortical areas associated with these latencies.
Gustatory activated regions in the cerebral cortex have not been identified precisely in humans. In this study we recorded the magnetic fields from the brain in response to two tastants, 1 M NaCl and 3 mM saccharin. We estimated the location of areas activated sequentially after the onset of stimulation with magnetic source imaging. We investigated the primary gustatory area (area G) precisely, and found it at the transition between the parietal operculum and the insular cortex. The central sulcus was activated less frequently than area G but with almost the same latency in cases of NaCl stimulation. Following area G, we found activation in several cortical regions, e.g. both the frontal operculum and the anterior part of the insula, the hippocampus, the parahippocampal gyrus and the superior temporal sulcus.
Human subjects rated the time course of the burn produced by three concentrations of capsaicin applied to the tongue via filter papers. Data were fit to a dynamic model composed of a level detector, a change detector, and a double integrator. These three processes responded differently to concentration. 6-n-Propyl-2-thiouracil (PROP) taster status correlated positively with the integrator process. Although a minority of subjects showed evidence of the integrator process, any subject with an integrator process at a given concentration also showed it at any higher concentration.
Evoked potentials are widely used in clinical medicine for objective evaluation of sensory disturbances. However, gustatory evoked potentials (GEPs) have not been extensively studied due to lack of agreement among investigators regarding the waveforms. In this study GEPs and gustatory magnetic fields (GEMfs) were simultaneously recorded from five subjects in response to 0.3 M NaCl in an attempt to establish GEP recording as an objective gustatometer. Each subject received a total of 240 stimulus presentations over six sessions. Three GEP components (P1, N1 and P2) were observed and correlated with their corresponding equivalent current dipoles (ECD1, ECD2 and ECD3, respectively). ECD1 was localized to area G in all subjects, P1 being the indicator of intact gustatory projection to area G. No significant GEP activity was detected during the time preceding P1, which suggests that there was no activity in cortical gyri other than that detected by magnetoencephalography. ECD2 and ECD3 were localized to various cortical structures, including the inferior insula and the superior temporal sulcus, indicating that N1 and P2 reflect higher order gustatory functions. The present results indicate that measurement of GEPs may be useful for objective evaluation of gustatory disturbance.
We examined the laterality of the human gustatory neural pathway by measuring gustatory-evoked magnetic fields (GEMfs) and demonstrating the activation of the human primary gustatory cortex (PGC). In patients whose chorda tympani nerve had been severed unilaterally on the right side, we stimulated the normal side (i.e., left side) of the chorda tympani nerve with NaCl solution using a device developed for measuring GEMfs. We used the whole-head magnetoencephalography system for recording GEMfs and analyzed the frequency and latency of PGC activation in each hemisphere. "The transitional cortex between the insula and the parietal operculum" was identified as PGC with the base of the central sulcus in this experiment. Significant difference was found in frequencies among bilateral, only-ipsilateral, and only-contralateral responses by the Friedman test (P < 0.05), and more frequent bilateral responses were observed than only-ipsilateral (P < 0.05) or only-contralateral responses (P < 0.01) by the multiple comparison tests. In the bilateral responses, the averaged activation latencies of the transitional cortex between the insula and the parietal operculum were not significantly different in both hemispheres. These results suggest that unilateral gustatory stimulation will activate the transitional cortex between the insula and the parietal operculum bilaterally in humans.
Evoked potentials are widely used in clinical medicine for objective evaluation of sensory disturbances. However, gustatory evoked potentials (GEPs) have not been extensively studied due to lack of agreement among investigators regarding the waveforms. In this study GEPs and gustatory magnetic fields (GEMfs) were simultaneously recorded from five subjects in response to 0.3 M NaCl in an attempt to establish GEP recording as an objective gustatometer. Each subject received a total of 240 stimulus presentations over six sessions. Three GEP components (P1, N1 and P2) were observed and correlated with their corresponding equivalent current dipoles (ECD1, ECD2 and ECD3, respectively). ECD1 was localized to area G in all subjects, P1 being the indicator of intact gustatory projection to area G. No significant GEP activity was detected during the time preceding P1, which suggests that there was no activity in cortical gyri other than that detected by magnetoencephalography. ECD2 and ECD3 were localized to various cortical structures, including the inferior insula and the superior temporal sulcus, indicating that N1 and P2 reflect higher order gustatory functions. The present results indicate that measurement of GEPs may be useful for objective evaluation of gustatory disturbance.
Chemosensory event-related potentials hold great promise for furthering the understanding of the olfactory system, the processing
of olfactory information, and disease processes affecting olfaction. Collection of this type of data has been difficult and
suggestions are presented to aid investigators new to this field. Suggestions for nomenclature, recording parameters, chemosensory
stimulation parameters and reporting conventions are discussed. Also discussed are the future directions of this field and
the current needs regarding the development of a normative database.
Despite numerous attempts, a satisfactory method of recording gustatory evoked potentials (GEPs) had not been found as yet. This study reports a new stimulation technique by which taste receptors can be stimulated selectively. Gaseous chemical stimuli of an approximately rectangular concentration course were presented to 5 subjects. Acetic acid at different concentrations was used as the stimulant. The EEG was recorded from standard 10/20 positions referred to A1. Taste receptors were activated in a sufficiently synchronous manner to evoke summated slow wave potentials in the central nervous system. Concordant with other cortical evoked potentials, the vertex was the site of the most pronounced deviations of GEPs.
Relationships between drinking behavior and electrical responses of the chorda tympani and lingual nerves were investigated in albino rats. An unacceptable concentration of quinine hydrochloride solution was 0.14–0.2% w/v, and that of tartaric acid was 4–8% w/v. Daily intakes of quinine hydrochloride and tartaric acid solutions decreased in proportion to the increase of the magnitude of neural response of the chorda tympani. Sucrose solutions were acceptable in all concentrations. The most acceptable concentration was about 10% w/v. Neural responses of the chorda tympani to sucrose solutions increased exponentially as the concentration was increased. The most acceptable concentration of sodium chloride solution was 1–2% w/v. Unacceptable concentrations were 6–8% w/v and greater. Responses of the chorda tympani increased exponentially as the concentration was increased. A few fibers in the lingual nerve which responded to mono-valent but not di-valent salt solutions in high concentration were found in rat. The role of these nerves in aversion to strong salt solutions was discussed.
While applying natural stimulation to the entire oral cavity, we recorded responses from 489 neurons (400 mechanoreceptive, 84 taste and 5 cold neurons) in the insular cortex of urethane-anesthetized rats. Intermingled with the mechanoreceptive neurons was a major group of taste neurons located in the granular or dysgranular insular area at levels of 2.55-1.20 mm anterior to the bed nucleus of the anterior commissure as stereotaxically located. Most of the taste neurons were also sensitive to mechanical stimulation of the oral and/or perioral tissue.
Despite numerous attempts, a satisfactory method of recording gustatory evoked potentials (GEPs) had not been found as yet. This study reports a new stimulation technique by which taste receptors can be stimulated selectively. Gaseous chemical stimuli of an approximately rectangular concentration course were presented to 5 subjects. Acetic acid at different concentrations was used as the stimulant. The EEG was recorded from standard 10/20 positions referred to A1. Taste receptors were activated in a sufficiently synchronous manner to evoke summated slow wave potentials in the central nervous system. Concordant with other cortical evoked potentials, the vertex was the site of the most pronounced deviations of GEPs. Potential amplitudes increased and latencies decreased with rising concentrations. After application of the local anaesthetic tetracaine hydrochloride (10 mg) to the tongue, GEPs and taste sensations were eliminated. In one patient ageusia coinciding with irradiation therapy (36 Gy) was proved by the attenuation of the GEPs. Also GEPs to sweet (chloroform), salty (ammonium chloride) and bitter (thujone) taste sensations were recorded for the first time.
Receptive properties of neurons at areas 3 and 1-2, and the gustatory area (area G) in the frontal operculum (Fop) and the neighboring areas were investigated in the cerebral cortex of Macaca irus and Macaca fuscata by applying mechanical and taste stimulation to the oral cavity and lips. Tactile neurons with different receptive properties were noted in areas 3, 1-2 and G. Areas 3 and G were packed with tongue neurons, though a considerable number of palate neurons were also found in area G, while area 1-2 was involved in representation of the tongue, palate, periodontia and lips. Both the anterior and posterior parts of the tongue were represented on these areas, and of the palate, the posterior part (the soft palate) was largely represented. The anterior and posterior periodontia were represented, without separation. Various tissues were represented with different laterality: Periodontia and the lips were most frequently represented bilaterally or contralaterally, but the tongue and palate often ipsilaterally. In area 6, the insula and other areas surrounding areas 3, 1-2 and G, tactile neurons were also found to have receptive fields on the lips, tongue, palate or periodontium, and the receptive fields on the tongue or palate were mainly bilateral. On the other hand, most of the taste neurons were located in area G and some in area 1-2 and the insula. The present study demonstrated that in macaque monkeys, tactile sensation of the oral cavity is represented on areas 3, 1-2 and G in the Fop as well as on the surrounding areas (e.g., area 6 and the insula), and taste sensation on areas G and 1-2 and the insula.
Separate taste examinations of each area of gustatory innervation are necessary in clinical practice in treating patients with taste disorders. We have developed our own electrogustometer with a dB scale and qualitative and quantitative clinical gustometry using filter-paper discs (the filter-paper disc method). this paper reports on our main basic studies in this field and new insights and experience gained in connection with the two gustometry procedures. Reference is made to the gustatory pathway, innervation area on the tongue and the soft palate, the argument against the localization theory of taste, the correlation between electrogustometry and the filter-paper disc method, differential diagnosis of taste disorders using both methods and the effective use of these methods in clinical practice. The effective use of both methods of measurements is important to give the physician assurance and confidence in the diagnosis and treatment of taste disorders.
The evoked cortical responses to taste solutions applied to the human tongue surface were recorded by the averaging technique.The response was characterized by two positive waves with onset latencies of approximately 150 msec and 500–1500 msec.The early wave was due to mechanical stimulation by pouring the solution on the tongue surface, and the late wave was the gustatory response.The gustatory response to acid and salt was significant, but that to sucrose and quinine hydrochloride was not visible as far as 40 responses were summated. The reasons for this effect are discussed.RésuméLes auteurs ont enregitré les réponses évoquées corticales moyennes à des solutions gustatives appliquées à la surface de la langue chez l'homme. Cette réponse se caractérise par deux ondes positives dont les latences de début sont approximativement 150 et 500–1500 msec.L'onde précoce est due à la stimulation mécanique par introduction de la solution sur la surface linguale; l'onde tardive est la réponse gustative proprement dite.La réponse gustative à l'acide et au sel est importante mais celle au sucrose et à l'hydrochloride de quinine n'est pas visible malgré la sommation de 40 réponses; les auteurs en discutent les raisons.
A general expression is developed for the quasi-static magnetic field outside an inhomogeneous nonmagnetic volume conductor containing internal electromotive forces. Multipole expansions for both the electric and magnetic fields are derived. It is shown that the external magnetic field vanishes under conditions of axial symmetry. The magnetic field for a dipole current source in a sphere is derived, and the effect of an eccentric spherical inhomogeneity is analyzed. Finally the magnetic dipole moment is calculated for a current dipole in a conducting prolate spheroid.
Magnetoencephalography (MEG) is a procedure that analyzes the magnetic responses of neurons. An MEG system with a 37-channel superconductivity quantum interference device (SQUID) was used to record magnetic signals from the human brain in response to tactile stimulations of the face and oral cavity. Six normal individuals were studied as well as three patients who had undergone hemiglossectomies as treatment for carcinoma of the tongue and reconstruction with a pectoralis major myocutaneous flap. When the locations of the magnetic responses having latencies of 40 ms from onset of tactile stimulation were identified, these corresponded to the primary somatosensory cortex. In patients whose tongues had been reconstructed with a pectoralis major myocutaneous flap, the magnetic response upon stimulation of the flap was recorded in a sensory cortical area identical to that corresponding to the tongue. MEG systems such as the one described permit functional mapping of the cerebral cortex on stimulating the face and oral cavity.
Electrogustometry (EGM) has a number of strengths and a few limitations in clinical use. The strengths of EGM are: (i) the range of measurements can be kept constant; (ii) quantitative control of the intensity of the stimulation is possible; (iii) only a short period of time is required for testing; (iv) it is possible to detect even slight taste disorders for which the patient has no subjective symptoms; (v) it is useful for topognosis of lesions of taste pathways and for determining prognosis; and (vi) it is the only quantitative method for diagnosing disorders of the glosssopharyngeal nerve. The limitations of EGM are: (i) it is not useful for determining or diagnosing some of the symptoms often complained of by patients with taste disorder, namely dissociated taste disorder, heterogeusia and spontaneous dysgeusia; and (ii) it is not useful for following the progress of taste disorder. The many strengths and few limitations of EGM make it the first choice among taste examinations. This paper describes the clinical use of EGM as well as discussing other taste examinations used in our taste clinic and, in particular, the advantages and disadvantages of filter paper disk testing with taste solutions.
Lysozyme is one of the sweet-tasting proteins. To clarify the structure-sweetness relationship and the basicity-sweetness relationship in lysozyme, we have generated lysozyme mutants with Pichia systems. Alanine substitution of lysine residues demonstrated that two out of six lysine residues, Lys13 and Lys96, are required for lysozyme sweetness, while the remaining four lysine residues do not play a significant role in the perception of sweetness. Arginine substitution of lysine residues revealed that the basicity, but not the shape, of the side chain plays a significant role in sweetness. Single alanine substitutions of arginine residues showed that three arginine residues, Arg14, Arg21, and Arg73, play significant roles in lysozyme sweetness, whereas Arg45, Arg68, Arg125 and chemical modification by 1,2-cyclohexanedione did not affect sweetness. From investigation of the charge-specific mutations, we found that the basicity of a broad surface region formed by five positively charged residues, Lys13, Lys96, Arg14, Arg21, and Arg73, is required for lysozyme sweetness. Differences in the threshold values among sweet-tasting proteins might be caused by the broadness and/or the density of charged residues on the protein surface.
The psychophysics of somatosensory chemoreception in the nose and mouth. Smell and taste in health and disease, TV Getchell
- Bg Green
- Ht Lawless
Model studies of magnetocardiogram
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- B D Geselowits