Gustatory Evoked Potentials Research Articles

Prolonged latency of the gustatory evoked potentials for sucrose solution in subjects living with obesity compared with normal-weight subjects.

A difference in cortical treatment of taste information could alter food intake promoting the development of obesity. The main purpose was to compare, in subjects living with obesity (OB) and normal-weight subjects (NW), the characteristics of gustatory evoked potentials (GEP) for sucrose solution (10 g.100 mL-1) before and after a standard lunch. The secondary objective was to evaluate the correlations between GEP and the plasmatic levels of acylated ghrelin, leptin, insulin and serotonin. Each subject had 2 randomized sessions spaced by an interval of 2 days. During one session, subjects were fasting and during the other, subjects took a lunch low in sugar. In each session, subjects had a blood test before a first GEP recording followed by a second GEP recording either after a lunch (feeding session) or no lunch (fasting session). Twenty-eight OB (BMI: 38.6 ± 9.0 kg.m-2) were matched to 22 NW (BMI: 22.3 ± 2.2 kg.m-2). GEP latencies were prolonged in OB regardless the sessions and the time before and after lunch, compared with NW (in Cz at the morning: 170 ± 33 ms vs 138 ± 25 ms respectively; p < 0.001). The increase in latency observed in NW after lunch was not observed in OB. Negative or positive correlations were noted in all participants between GEP latencies and ghrelin, leptin, insulin plasmatic levels (P1Cz, r = -0.38, r = 0.33, r = 0.37 respectively, p < 0.0001). This study highlights a slower activation in the taste cortex in OB compared with NW.

Changes in Taste Perception in Patients with Minor and Major Cognitive Impairment Linked to Alzheimer's Disease Recorded by Gustatory Evoked Potentials.

The need for early diagnosis biomarkers in Alzheimer's disease (AD) is growing. Only few studies have reported gustatory dysfunctions in AD using subjective taste tests. The main purpose of the study was to explore gustatory functions using subjective taste tests and recordings of gustatory evoked potentials (GEPs) for sucrose solution in patients with minor or major cognitive impairment (CI) linked to AD, and to compare them with healthy controls. The secondary objective was to evaluate the relationships between GEPs and the results of cognitive assessments and fasting blood samples. A total of 45 subjects (15 healthy subjects, 15 minor CI patients, 15 major CI patients) were included to compare their gustatory functions and brain activity by recording GEPs in response to a sucrose stimulation. CI groups were combined in second analyses in order to keep a high power in the study. Correlations were made with cognitive scores and hormone levels (ghrelin, leptin, insulin, serotonin). Increased P1 latencies and reduced N1 amplitudes were observed in minor or major patients compared to controls. GEPs were undetectable in 6 major and 4 minor CI patients. Thresholds for sucrose detection were significantly higher in the major CI group than in controls or the minor CI group. No correlation was found with hormone levels. The cortical processing of sensory taste information seems to be altered in patients with minor or major CI linked to AD. This disturbance was identifiable with subjective taste tests only later, at the major CI stage.

Differential Cerebral Gustatory Responses to Sucrose, Aspartame, and Stevia Using Gustatory Evoked Potentials in Humans.

Aspartame and Stevia are widely substituted for sugar. Little is known about cerebral activation in response to low-caloric sweeteners in comparison with high-caloric sugar, whereas these molecules lead to different metabolic effects. We aimed to compare gustatory evoked potentials (GEPs) obtained in response to sucrose solution in young, healthy subjects, with GEPs obtained in response to aspartame and Stevia. Twenty healthy volunteers were randomly stimulated with three solutions of similar intensities of sweetness: Sucrose 10 g/100 mL of water, aspartame 0.05 g/100 mL, and Stevia 0.03 g/100 mL. GEPs were recorded with EEG (Electroencephalogram) electrodes. Hedonic values of each solution were evaluated using the visual analog scale (VAS). The main result was that P1 latencies of GEPs were significantly shorter when subjects were stimulated by the sucrose solution than when they were stimulated by either the aspartame or the Stevia one. P1 latencies were also significantly shorter when subjects were stimulated by the aspartame solution than the Stevia one. No significant correlation was noted between GEP parameters and hedonic values marked by VAS. Although sucrose, aspartame, and Stevia lead to the same taste perception, cerebral activation by these three sweet solutions are different according to GEPs recording. Besides differences of taste receptors and cerebral areas activated by these substances, neural plasticity, and change in synaptic connections related to sweet innate preference and sweet conditioning, could be the best hypothesis to explain the differences in cerebral gustatory processing after sucrose and sweeteners activation.

Taste Perception and Cerebral Activity in the Human Gustatory Cortex Induced by Glucose, Fructose, and Sucrose Solutions.

Glucose, fructose, and sucrose are important carbohydrates in Western diets with particular sweetness intensity and metabolisms. No study has compared their cerebral detection and their taste perception. Gustatory evoked potentials (GEPs), taste detection thresholds, intensity perception, and pleasantness were compared in response to glucose, fructose, and sucrose solutions at similar sweetness intensities and at identical molar concentrations. Twenty-three healthy subjects were randomly stimulated with 3 solutions of similar sweetness intensity (0.75 M of glucose, 0.47 M of fructose and 0.29 M of sucrose - sit. A), and with an identical molar concentration (0.29 M - sit. B). GEPs were recorded at gustatory cortex areas. Intensity perception and hedonic values of each solution were evaluated as were gustatory thresholds of the solutions. No significant difference was observed concerning the GEP characteristics of the solutions according to their sweetness intensities (sit. A) or their molar concentration (sit. B). In sit. A, the 3 solutions were perceived to have similar intensities and induced similar hedonic sensations. In sit. B, the glucose solution was perceived to be less intense and pleasant than the fructose and the sucrose solutions (P < 0.001) and the fructose solution was perceived to be less intense and pleasant than the sucrose (P < 0.001). Since GEP recordings were similar for glucose, fructose, and sucrose solutions whatever the concentrations, activation of same taste receptor induces similar cortical activation, even when the solutions were perceived differently. Sweet taste perception seems to be encoded by a complex chemical cerebral neuronal network.

Cerebral gustatory activation in response to free fatty acids using gustatory evoked potentials in humans

There is some evidence of specific oro-detection of FFAs in rodents and humans. The aim of this study was to record gustatory evoked potentials (GEPs) in response to FFA solutions and to compare GEPs in response to linoleic acid solution with GEPs obtained after stimulation with sweet and salty tastants. Eighteen healthy men were randomly stimulated with fatty (linoleic acid), sweet (sucrose), and salty (NaCl) solutions at two concentrations in the first experiment. Control recordings (n = 14) were obtained during stimulation by a paraffin oil mixture without FFA or by water. In the second experiment, 28 men were randomly stimulated with five FFA solutions and a paraffin emulsion. GEPs were recorded with electroencephalographic electrodes at Cz, Fz, and Pz. GEPs were observed in response to FFA in all participants. GEP characteristics did not differ according to the quality and the concentration of the solutions in the first experiment and according to the FFA in the second experiment. This study describes for the first time GEPs in response to FFA and demonstrates that the presence of FFA in the mouth triggers an activation of the gustatory cortex. These data reinforce the concept that fat taste could be the sixth primary taste.

Preference for Sucrose Solutions Modulates Taste Cortical Activity in Humans.

High time resolution is required to reliably measure neuronal activity in the gustatory cortex in response to taste stimuli. Hedonic aspects of gustatory processing have never been explored using gustatory evoked potentials (GEPs), a high-time-resolution technique. Our aim was to study cerebral processing of hedonic taste in humans using GEPs in response to sucrose solutions in subjects with different ratings of pleasantness regarding sucrose. In this exploratory study, 30 healthy volunteers were randomly stimulated with 3 sucrose solutions. The sucrose stimulus was presented to the tongue for 1s 20 times. GEPs were recorded from 9 cortical sites with EEG sensors at Cz, Fz, Pz, C3, C4, F3, F4, Fp1, and Fp2 (10/20 system). The main result was that subjects who preferred the high-concentration (20g/100mL) sucrose solution had higher GEP amplitudes on the Pz, Cz, and Fz electrodes than did subjects who preferred the low-concentration (5g/100mL) or the moderate-concentration (10g/100mL) solutions regardless of stimulus intensity. The difference in P1N1 amplitude on the Pz, Cz, and Fz electrodes according to sucrose preference of the subjects was described with stronger significance with stimulation by the 20 g-sucrose solution than by the 5 and 10g sucrose solutions. Using the reliable and safe GEP technique, we provide an original demonstration of variability of the gustatory response on the Pz, Cz, and Fz electrodes according to a sweet preference in humans. Further studies are needed to correlate the electric signal recorded by surface electrodes to the neural generator.

Prandial States Modify the Reactivity of the Gustatory Cortex Using Gustatory Evoked Potentials in Humans.

Previous functional Magnetic Resonance Imaging studies evaluated the role of satiety on cortical taste area activity and highlighted decreased activation in the orbito-frontal cortex when food was eaten until satiation. The modulation of orbito-frontal neurons (secondary taste area) by ad libitum food intake has been associated with the pleasantness of the food's flavor. The insula and frontal operculum (primary taste area) are also involved in reward processing. The aim was to compare human gustatory evoked potentials (GEP) recorded in the primary and secondary gustatory cortices in a fasted state with those after food intake. Fifteen healthy volunteers were enrolled in this observational study. In each of two sessions, two GEP recordings were performed (at 11:00 am and 1:30 pm) in response to sucrose gustatory stimulation, and a sucrose-gustatory threshold was determined. During one session, a standard lunch was provided between the two GEP recordings. During the other session, subjects had nothing to eat. Hunger sensation, wanting, liking, and the perception of the solution's intensity were evaluated with visual analog scales. GEP latencies measured in the Pz (p < 0.001), Cz (p < 0.01), Fz (p < 0.001) recordings (primary taste area) were longer after lunch than in the pre-prandial condition. Fp1 and Fp2 latencies (secondary taste area) tended to be longer after lunch, but the difference was not significant. No difference was observed for the sucrose-gustatory threshold regardless of the session and time. Modifications in the primary taste area activity during the post-prandial period occurred regardless of the nature of the food eaten and could represent the activity of the frontal operculum and insula, which was recently shown to be modulated by gut signals (GLP-1, CCK, ghrelin, or insulin) through vagal afferent neurons or metabolic changes of the internal milieu after nutrient absorption. This trial was registered at clinicalstrials.gov as NCT02472444.

電気味覚計を用いた味覚誘発電位記録法の検討

The purpose of this study was to determine whether gustatory-evoked potentials are useful or not for an objective evaluation of taste. Fifteen healthy subjects were selected. Electrical stimulation was delivered to the taste buds area of the tongue (chorda tympani, glossopharyngeal nerve area) and the soft palate (greater petrosal nerve area). Electric taste threshold and quality of judgment were measured under 7 conditions of stimulus duration (1,000, 500, 300, 200, 120, 100, and 70 msec). Electroencephalogram (EEG) was recorded at 19 sites of the 10-20 International System standard. The results from 40 presentations were averaged. Electric taste threshold was significantly higher when below 100 msec (chorda tympani nerve area), 120 msec (glossopharyngeal nerve area), and 200 msec (greater petrosal nerve area). In taste quality judgment, the number of subjects in whom taste was induced decreased in the stimulus duration condition of less than 100 msec (chorda tympani, glossapharyngeal), and decreased in all of the stimulus duration conditions (greater petrosal nerve area). In the cerebral-evoked potentials noted at 9 sites, three peaks (P1, N1, P2) were observed when taste was induced in the subjects. On the other hand, P2 wave was indistinct when only touch was induced. As stimulus intensity increased, peak latencies could not be seen to change significantly, but N1-P2 amplitude increased significantly. The latencies in these peaks were similar to typical potentials in the literature (K-H Plattig, 1971). P2 was considered to be a gustatory-evoked potential. Investigation of this response has shown it to be a useful method for objective examination of taste.

A Review of Objective Measures of Gustatory Function

Several studies of diagnostic tests of gustatory function have been reported. Results show that none of the subjective tests are satisfactory because they cannot detect psychogenic disease or malingering. Of the objective modalities that have been investigated, gustatory-evoked potential testing has been the most widely studied because it does not require expensive equipment and can be used in multicenter studies. The techniques developed to date for measuring gustatory-evoked potentials are not yet clinically useful for diagnosing taste disorders. Future directions for improving this method of evaluating gustatory function include improving stimulation methods and equipment, in order to obtain better stimulation-related potentials and better means of distinguishing between normal and abnormal gustatory-evoked potential patterns, and applying these new standards to the evaluation of data.

The application of d.c. electrical stimulation in evoking and recording gustatory brain potentials

Evidence exists which supports the hypothesis that electrical stimulation of appropriate parameters can fulfil the fundamental requirements for an effective evoked potential taste stimulus. Nevertheless, it had previously been considered that electrical taste stimulation is inadequate for evoking gustatory brain potentials. Consequently, the majority of the earlier attempts to record gustatory evoked potentials (GEPs) reported in the literature have employed chemical stimulus techniques. The design of an electrical taste stimulator and its interface to an evoked potential recording unit is described. The first human brain potentials recorded with this system are presented, among which are those attributable to taste pathway activation. Following future work to unequivocally confirm that taste evoked brain potentials are achievable with this system, it has potential to become a clinically valuable tool.

A new gustometer for computer evaluation of taste responses in men and animals.

Many previous attempts to acquire gustatory evoked potentials (GEPs) in both men and animals could not satisfy strict requirements on purely unimodal stimulation free of contaminating artifacts. Therefore we developed an advanced new gustometer, based on our previous experience on olfactory evoked potentials, especially on magnetic valves as also used in our "Erlangen olfactometer". Several newly constructed magnetic valves were tested; the best one (MV3) enables us to fulfill the following indispensable conditions for proper averaging by computer: precise onset and duration of stimulus, and shortest possible stimulus rise and fall times. Tactile artifacts were avoided by constant rinsing of the tongue with neutral water, in which the taste stimulus was embedded without turbulences. By recording and averaging the galvanic skin response (GSR) at the same time, its influence on GEPs was compensated. To evaluate successfully objective correlates of taste sensation in man is believed to be of great basic and clinical importance.

Gustatory evoked potentials in man

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 re recorded for the first