Etude du contrôle hédonique de la prise alimentaire par l'analyse des potentiels évoqués gustatifs

Hedonic control of food intake has been studied using neurophysiological investigations in animals and functional imaging in humans. Gustatory evoked potentials (GEPs), a higher time resolution technique than functional imaging, have never been used for this purpose. The first aim of this thesis was to establish a reliable recording of GEPs in humans, in response to a sapid stimulus. The second aim was to determine the GEPs modifications according to the hedonic value of food intake. GEPs recording was performed in response to an intermittent stimulation of a sapid solution in more than 100 young healthy subjects. The comparisons between cerebral recordings in response to water or paraffin oil, non palatable solutions, and in response to sapid solutions (sucrose, sodium chlorure and fatty acids) allow us to advance strong arguments for the gustative nature of the recorded evoked potentials. GEPs analysis underlined changes in cerebral activation according to the hedonic value of the stimulus. These changes in cerebral activation were highlighted by modifications of GEPs latency or amplitude. Several physiological situations, marked by different pleasantness of food stimulation, were studied: before/after food intake, stimulation by sweet solutions with different concentrations or different caloric contents, stimulation by fatty acids. Moreover, GEPs in response to long chain fatty acids (linoleic acids) were recorded, reinforcing the hypothesis that fatty acids could be the sixth primary flavor.Les techniques d’électrophysiologie chez les animaux et d’imagerie fonctionnelle chez l’Homme ont permis d’étudier le contrôle hédonique de la prise alimentaire. Ce contrôle hédonique n’a cependant jamais été exploré chez l’Homme par l’étude des potentiels évoqués gustatifs (PEG), de meilleure résolution temporelle que l’imagerie fonctionnelle. Le premier objectif de la thèse a été de mettre au point une technique fiable et reproductible de recueil des PEG, en regard des aires cérébrales gustatives, en réponse à une stimulation sapide. Le deuxième objectif a été d’étudier les variations des PEG en fonction de la valeur hédonique de la prise alimentaire. Le travail de thèse a permis de mettre au point l’enregistrement des PEG, réalisés chez plus de 100 jeunes sujets sains. Les comparaisons effectuées entre les enregistrements cérébraux obtenus en réponse à l’eau seule ou à l’huile de paraffine, solutions non palatables, et après stimulation par une solution sapide ont permis d’apporter des arguments forts en faveur de l’origine gustative des potentiels évoqués enregistrés. L’analyse des PEG a permis de mettre en évidence des modifications de l’activation cérébrale en fonction du plaisir alimentaire, traduites par des changements de latence ou d’amplitude des PEG. Plusieurs situations connues pour faire varier le plaisir alimentaire ont été étudiées : avant/après repas ; stimulation par des solutions sucrées d’intensités différentes ou de valeurs énergétiques différentes ; stimulation par des acides gras. Des PEG en réponse aux acides gras à longue chaine (acides linoléiques) ont été enregistrés par ce biais, renforçant l’hypothèse du «gras» en tant que sixième saveur primaire

Study of hedonic control of food intake using gustatory evoked potentials

Les techniques d’électrophysiologie chez les animaux et d’imagerie fonctionnelle chez l’Homme ont permis d’étudier le contrôle hédonique de la prise alimentaire. Ce contrôle hédonique n’a cependant jamais été exploré chez l’Homme par l’étude des potentiels évoqués gustatifs (PEG), de meilleure résolution temporelle que l’imagerie fonctionnelle. Le premier objectif de la thèse a été de mettre au point une technique fiable et reproductible de recueil des PEG, en regard des aires cérébrales gustatives, en réponse à une stimulation sapide. Le deuxième objectif a été d’étudier les variations des PEG en fonction de la valeur hédonique de la prise alimentaire. Le travail de thèse a permis de mettre au point l’enregistrement des PEG, réalisés chez plus de 100 jeunes sujets sains. Les comparaisons effectuées entre les enregistrements cérébraux obtenus en réponse à l’eau seule ou à l’huile de paraffine, solutions non palatables, et après stimulation par une solution sapide ont permis d’apporter des arguments forts en faveur de l’origine gustative des potentiels évoqués enregistrés. L’analyse des PEG a permis de mettre en évidence des modifications de l’activation cérébrale en fonction du plaisir alimentaire, traduites par des changements de latence ou d’amplitude des PEG. Plusieurs situations connues pour faire varier le plaisir alimentaire ont été étudiées : avant/après repas ; stimulation par des solutions sucrées d’intensités différentes ou de valeurs énergétiques différentes ; stimulation par des acides gras. Des PEG en réponse aux acides gras à longue chaine (acides linoléiques) ont été enregistrés par ce biais, renforçant l’hypothèse du «gras» en tant que sixième saveur primaire.Hedonic control of food intake has been studied using neurophysiological investigations in animals and functional imaging in humans. Gustatory evoked potentials (GEPs), a higher time resolution technique than functional imaging, have never been used for this purpose. The first aim of this thesis was to establish a reliable recording of GEPs in humans, in response to a sapid stimulus. The second aim was to determine the GEPs modifications according to the hedonic value of food intake. GEPs recording was performed in response to an intermittent stimulation of a sapid solution in more than 100 young healthy subjects. The comparisons between cerebral recordings in response to water or paraffin oil, non palatable solutions, and in response to sapid solutions (sucrose, sodium chlorure and fatty acids) allow us to advance strong arguments for the gustative nature of the recorded evoked potentials. GEPs analysis underlined changes in cerebral activation according to the hedonic value of the stimulus. These changes in cerebral activation were highlighted by modifications of GEPs latency or amplitude. Several physiological situations, marked by different pleasantness of food stimulation, were studied: before/after food intake, stimulation by sweet solutions with different concentrations or different caloric contents, stimulation by fatty acids. Moreover, GEPs in response to long chain fatty acids (linoleic acids) were recorded, reinforcing the hypothesis that fatty acids could be the sixth primary flavor

Perception des acides gras et potentiels évoqués gustatifs : application dans l’obésité

International audienceFat taste as a primary taste is a new concept which can affect feeding behavior. Free fatty acids could activate the gustatory afferent pathway as another primary taste (sweet, salt, bitter, sour, umami). Our team demonstrates this activation by recording cerebral gustatory evoked potentials, in response to several solutions of free fatty acids. These new data could have a strong impact on the understanding of the physiopathology of obesity. In part, overeating in obesity is due to alteration of the homeostatic feedback created by the peripheral energetic status. Food is a key-point of the hedonic feeding behavior based to the reward system, which has consequences on calories consumption and sensory abilities. In this background, fat taste, altered in obesity for some authors, could be only the consequence of overweight. Fat taste could be modified by the feeding behavior and the body composition, because of alteration of the reward system involved into the acceptation of the palatable energy-rich foods such as lipids or carbohydrates. Alteration of the reward system should be taken into account in the physiopathology of obesity, and offers promising prospects about diagnosis and future treatment of obesity

Taste disorders in disease

International audienceAmong the different sensory systems, gustation is one of the most elaborate. In its sensory task, gustation is helped by interactions with other sensory systems (olfaction, vision, auditory and somatosensory, trigeminal and thermal sensations). It allows the detection and identification of soluble compounds which can be ingested or must be avoided. This function is fundamental to ingestive behavior (energy intake and selection of nutrients) in order to meet physiological needs. Taste is also fundamental to the genesis of hedonic sensations and therefore the desire to eat (appetite). The tasting step is also the first stage of the digestion, absorption, and storage of nutrients due to anticipatory reflexes. Taste disorders are therefore not simple hedonic alterations of the Epicurean canon of gastronomy; taste disorders can worsen and even compromise vital functions (malnutrition and aggravation of an underlying disease) and they always reduce quality of life. Many drugs and numerous diseases can cause gustatory loss. The mechanisms leading to taste alteration are varied. In medical practice, taste problems are frequent but not diagnosed often enough, in particular in metabolic syndrome and obesity, in neurodegenerative diseases, and in cancer. Increasing knowledge of taste disorders in disease could improve our understanding of taste pathophysiology and the prevention of malnutrition by diets adapted to taste impairment

COVID 19-Induced Smell and Taste Impairments: Putative Impact on Physiology

International audienceSmell and taste impairments are recognized as common symptoms in COVID 19 patients even in an asymptomatic phase. Indeed, depending on the country, in up to 85-90% of cases anosmia and dysgeusia are reported. We will review briefly the main mechanisms involved in the physiology of olfaction and taste focusing on receptors and transduction as well as the main neuroanatomical pathways. Then we will examine the current evidences, even if still fragmented and unsystematic, explaining the disturbances and mode of action of the virus at the level of the nasal and oral cavities. We will focus on its impact on the peripheral and central nervous system. Finally, considering the role of smell and taste in numerous physiological functions, especially in ingestive behavior, we will discuss the consequences on the physiology of the patients as well as management regarding food intake

potentiels évoqués gustatifs chez l'Homme en réponse à une stimulation sucrée

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Preference for Sucrose Solutions Modulates Taste Cortical Activity in Humans

International audienceHigh 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 1 s 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 (20 g/100 mL) sucrose solution had higher GEP amplitudes on the Pz, Cz, and Fz electrodes than did subjects who preferred the low-concentration (5 g/100 mL) or the moderate-concentration (10 g/100 mL) 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

Sens chimiques et maladies métaboliques chez l’Homme

International audienceTaste and smell are described as chemical senses because of their molecule detection characteristics. They provide sensory information whose main role is the regulation of food intake. Because of this, many authors have theorized a link between alteration of these senses and the occurrence of metabolic diseases such as type 2 diabetes (T2D), obesity or dyslipidemia. We explore these links in a review of the literature. Studies on T2D do not always show a link between this disease and taste alteration, although some more recent studies are positive. However, there is a more consistent report of an alteration of the sense of smell. In the same way, a link between obesity and alterations of taste and smell is not found in all studies. Subjective modifications of taste and smell after bariatric surgery have been reported. No association was found between smell and dyslipidemia in the only study found in our literature review. These differences between studies may be explained by the lack of standardization of the measurement of taste and smell and by the relatively small number of people in the studies concerned. Furthermore, the existence of a possible causality between alteration of the chemical senses and the occurrence of a metabolic disease is not known to date, and further studies are needed to explore these areas.Le goût et l’odorat sont décrits comme les sens chimiques en raison de leur caractéristique de détection de molécules. Ils apportent une information sensorielle dont le rôle principal est la régulation des apports alimentaires. En raison de cette fonction, de nombreux auteurs ont théorisé un lien entre l’altération de ces sens et la survenue de maladies métaboliques, telles que le diabète de type 2 (DT2), l’obésité ou les dyslipidémies. Nous avons entrepris une revue de la littérature pour explorer ces liens. Les études sur le DT2 ne mettent pas toujours en évidence de lien entre cette maladie et une altération du goût, certaines études plus récentes sont toutefois positives. On rapporte, en revanche, de manière plus consensuelle, une altération de l’odorat. De la même manière, le lien entre obésité et altérations du goût et de l’odorat n’est pas retrouvé dans toutes les études. Il est mis en évidence une modification subjective du goût et de l’odorat après chirurgie bariatrique. Il n’a pas été objectivée d’association entre l’odorat et les dyslipidémies dans l’unique étude retrouvée. Ces différences entre les études peuvent s’expliquer par une absence de standardisation des techniques de mesure du goût et de l’odorat et par des effectifs de patients assez faibles dans les études concernées. Par ailleurs, l’existence d’une éventuelle causalité entre altération des sens chimiques et survenue d’une maladie métabolique n’est pas connue à ce jour, d’autres études sont nécessaires pour explorer ces axes