Le sens du goût chez l'aveugle congénital

Thèse réalisée en collaboration avec le Département de neurosciences et pharmacologie de l'Université de Copenhague, Danemark.

Effetti dell'integrazione visuo-acustica in pazienti con disturbo di campo visivo

Human brain is provided with a flexible audio-visual system, which interprets and guides responses to external events according to spatial alignment, temporal synchronization and effectiveness of unimodal signals. The aim of the present thesis was to explore the possibility that such a system might represent the neural correlate of sensory compensation after a damage to one sensory pathway. To this purpose, three experimental studies have been conducted, which addressed the immediate, short-term and long-term effects of audio-visual integration on patients with Visual Field Defect (VFD). Experiment 1 investigated whether the integration of stimuli from different modalities (cross-modal) and from the same modality (within-modal) have a different, immediate effect on localization behaviour. Patients had to localize modality-specific stimuli (visual or auditory), cross-modal stimulus pairs (visual-auditory) and within-modal stimulus pairs (visual-visual). Results showed that cross-modal stimuli evoked a greater improvement than within modal stimuli, consistent with a Bayesian explanation. Moreover, even when visual processing was impaired, cross-modal stimuli improved performance in an optimal fashion. These findings support the hypothesis that the improvement derived from multisensory integration is not attributable to simple target redundancy, and prove that optimal integration of cross-modal signals occurs in processing stage which are not consciously accessible. Experiment 2 examined the possibility to induce a short term improvement of localization performance without an explicit knowledge of visual stimulus. Patients with VFD and patients with neglect had to localize weak sounds before and after a brief exposure to a passive cross-modal stimulation, which comprised spatially disparate or spatially coincident audio-visual stimuli. After exposure to spatially disparate stimuli in the affected field, only patients with neglect exhibited a shifts of auditory localization toward the visual attractor (the so called Ventriloquism After-Effect). In contrast, after adaptation to spatially coincident stimuli, both neglect and hemianopic patients exhibited a significant improvement of auditory localization, proving the occurrence of After Effect for multisensory enhancement. These results suggest the presence of two distinct recalibration mechanisms, each mediated by a different neural route: a geniculo-striate circuit and a colliculus-extrastriate circuit respectively. Finally, Experiment 3 verified whether a systematic audio-visual stimulation could exert a long-lasting effect on patients’ oculomotor behaviour. Eye movements responses during a visual search task and a reading task were studied before and after visual (control) or audio-visual (experimental) training, in a group of twelve patients with VFD and twelve controls subjects. Results showed that prior to treatment, patients’ performance was significantly different from that of controls in relation to fixations and saccade parameters; after audiovisual training, all patients reported an improvement in ocular exploration characterized by fewer fixations and refixations, quicker and larger saccades, and reduced scanpath length. Similarly, reading parameters were significantly affected by the training, with respect to specific impairments observed in left and right hemisphere–damaged patients. The present findings provide evidence that a systematic audio-visual stimulation may encourage a more organized pattern of visual exploration with long lasting effects. In conclusion, results from these studies clearly demonstrate that the beneficial effects of audio-visual integration can be retained in absence of explicit processing of visual stimulus. Surprisingly, an improvement of spatial orienting can be obtained not only when a on-line response is required, but also after either a brief or a long adaptation to audio-visual stimulus pairs, so suggesting the maintenance of mechanisms subserving cross-modal perceptual learning after a damage to geniculo-striate pathway. The colliculus-extrastriate pathway, which is spared in patients with VFD, seems to play a pivotal role in this sensory compensation.

Neural basis of visual deficits recovery: visual residual functions and multisensory integration.

The ability of integrating into a unified percept sensory inputs deriving from different sensory modalities, but related to the same external event, is called multisensory integration and might represent an efficient mechanism of sensory compensation when a sensory modality is damaged by a cortical lesion. This hypothesis has been discussed in the present dissertation. Experiment 1 explored the role of superior colliculus (SC) in multisensory integration, testing patients with collicular lesions, patients with subcortical lesions not involving the SC and healthy control subjects in a multisensory task. The results revealed that patients with collicular lesions, paralleling the evidence of animal studies, demonstrated a loss of multisensory enhancement, in contrast with control subjects, providing the first lesional evidence in humans of the essential role of SC in mediating audio-visual integration. Experiment 2 investigated the role of cortex in mediating multisensory integrative effects, inducing virtual lesions by inhibitory theta-burst stimulation on temporo-parietal cortex, occipital cortex and posterior parietal cortex, demonstrating that only temporo-parietal cortex was causally involved in modulating the integration of audio-visual stimuli at the same spatial location. Given the involvement of the retino-colliculo-extrastriate pathway in mediating audio-visual integration, the functional sparing of this circuit in hemianopic patients is extremely relevant in the perspective of a multisensory-based approach to the recovery of unisensory defects. Experiment 3 demonstrated the spared functional activity of this circuit in a group of hemianopic patients, revealing the presence of implicit recognition of the fearful content of unseen visual stimuli (i.e. affective blindsight), an ability mediated by the retino-colliculo-extrastriate pathway and its connections with amygdala. Finally, Experiment 4 provided evidence that a systematic audio-visual stimulation is effective in inducing long-lasting clinical improvements in patients with visual field defect and revealed that the activity of the spared retino-colliculo-extrastriate pathway is responsible of the observed clinical amelioration, as suggested by the greater improvement observed in patients with cortical lesions limited to the occipital cortex, compared to patients with lesions extending to other cortical areas, found in tasks high demanding in terms of spatial orienting. Overall, the present results indicated that multisensory integration is mediated by the retino-colliculo-extrastriate pathway and that a systematic audio-visual stimulation, activating this spared neural circuit, is able to affect orientation towards the blind field in hemianopic patients and, therefore, might constitute an effective and innovative approach for the rehabilitation of unisensory visual impairments.

Impact de la cécité sur le système nociceptif

La vision joue un rôle très important dans la prévention du danger. La douleur a aussi pour fonction de prévenir les lésions corporelles. Nous avons donc testé l’hypothèse qu’une hypersensibilité à la douleur découlerait de la cécité en guise de compensation sensorielle. En effet, une littérature exhaustive indique qu’une plasticité intermodale s’opère chez les non-voyants, ce qui module à la hausse la sensibilité de leurs sens résiduels. De plus, plusieurs études montrent que la douleur peut être modulée par la vision et par une privation visuelle temporaire. Dans une première étude, nous avons mesuré les seuils de détection thermique et les seuils de douleur chez des aveugles de naissance et des voyants à l’aide d’une thermode qui permet de chauffer ou de refroidir la peau. Les participants ont aussi eu à quantifier la douleur perçue en réponse à des stimuli laser CO2 et à répondre à des questionnaires mesurant leur attitude face à des situations douloureuses de la vie quotidienne. Les résultats obtenus montrent que les aveugles congénitaux ont des seuils de douleur plus bas et des rapports de douleur plus élevés que leurs congénères voyants. De plus, les résultats psychométriques indiquent que les non-voyants sont plus attentifs à la douleur. Dans une deuxième étude, nous avons mesuré l’impact de l'expérience visuelle sur la perception de la douleur en répliquant la première étude dans un échantillon d’aveugles tardifs. Les résultats montrent que ces derniers sont en tous points similaires aux voyants quant à leur sensibilité à la douleur. Dans une troisième étude, nous avons testé les capacités de discrimination de température des aveugles congénitaux, car la détection de changements rapides de température est cruciale pour éviter les brûlures. Il s’est avéré que les aveugles de naissance ont une discrimination de température plus fine et qu’ils sont plus sensibles à la sommation spatiale de la chaleur. Dans une quatrième étude, nous avons examiné la contribution des fibres A∂ et C au traitement nociceptif des non-voyants, car ces récepteurs signalent la première et la deuxième douleur, respectivement. Nous avons observé que les aveugles congénitaux détectent plus facilement et répondent plus rapidement aux sensations générées par l’activation des fibres C. Dans une cinquième et dernière étude, nous avons sondé les changements potentiels qu’entrainerait la perte de vision dans la modulation descendante des intrants nociceptifs en mesurant les effets de l’appréhension d’un stimulus nocif sur la perception de la douleur. Les résultats montrent que, contrairement aux voyants, les aveugles congénitaux voient leur douleur exacerbée par l’incertitude face au danger, suggérant ainsi que la modulation centrale de la douleur est facilitée chez ces derniers. En gros, ces travaux indiquent que l’absence d’expérience visuelle, plutôt que la cécité, entraine une hausse de la sensibilité nociceptive, ce qui apporte une autre dimension au modèle d’intégration multi-sensorielle de la vision et de la douleur.

Impact de la cécité sur le système nociceptif

La vision joue un rôle très important dans la prévention du danger. La douleur a aussi pour fonction de prévenir les lésions corporelles. Nous avons donc testé l’hypothèse qu’une hypersensibilité à la douleur découlerait de la cécité en guise de compensation sensorielle. En effet, une littérature exhaustive indique qu’une plasticité intermodale s’opère chez les non-voyants, ce qui module à la hausse la sensibilité de leurs sens résiduels. De plus, plusieurs études montrent que la douleur peut être modulée par la vision et par une privation visuelle temporaire. Dans une première étude, nous avons mesuré les seuils de détection thermique et les seuils de douleur chez des aveugles de naissance et des voyants à l’aide d’une thermode qui permet de chauffer ou de refroidir la peau. Les participants ont aussi eu à quantifier la douleur perçue en réponse à des stimuli laser CO2 et à répondre à des questionnaires mesurant leur attitude face à des situations douloureuses de la vie quotidienne. Les résultats obtenus montrent que les aveugles congénitaux ont des seuils de douleur plus bas et des rapports de douleur plus élevés que leurs congénères voyants. De plus, les résultats psychométriques indiquent que les non-voyants sont plus attentifs à la douleur. Dans une deuxième étude, nous avons mesuré l’impact de l'expérience visuelle sur la perception de la douleur en répliquant la première étude dans un échantillon d’aveugles tardifs. Les résultats montrent que ces derniers sont en tous points similaires aux voyants quant à leur sensibilité à la douleur. Dans une troisième étude, nous avons testé les capacités de discrimination de température des aveugles congénitaux, car la détection de changements rapides de température est cruciale pour éviter les brûlures. Il s’est avéré que les aveugles de naissance ont une discrimination de température plus fine et qu’ils sont plus sensibles à la sommation spatiale de la chaleur. Dans une quatrième étude, nous avons examiné la contribution des fibres A∂ et C au traitement nociceptif des non-voyants, car ces récepteurs signalent la première et la deuxième douleur, respectivement. Nous avons observé que les aveugles congénitaux détectent plus facilement et répondent plus rapidement aux sensations générées par l’activation des fibres C. Dans une cinquième et dernière étude, nous avons sondé les changements potentiels qu’entrainerait la perte de vision dans la modulation descendante des intrants nociceptifs en mesurant les effets de l’appréhension d’un stimulus nocif sur la perception de la douleur. Les résultats montrent que, contrairement aux voyants, les aveugles congénitaux voient leur douleur exacerbée par l’incertitude face au danger, suggérant ainsi que la modulation centrale de la douleur est facilitée chez ces derniers. En gros, ces travaux indiquent que l’absence d’expérience visuelle, plutôt que la cécité, entraine une hausse de la sensibilité nociceptive, ce qui apporte une autre dimension au modèle d’intégration multi-sensorielle de la vision et de la douleur.

The influence of changing nicotine to tar ratios on human puffing behaviour and perceived sensory response

Rationale. Smokers modify their smoking behaviour when switching from their usual product to higher or lower tar and nicotine-yield cigarettes. Objective. The aims of the current study were to assess the influence of varying nicotine yields at constant tar yield on human puffing measures, nicotine deliveries under human smoking conditions and the sensory response to mainstream cigarette smoke. These assessments would allow an evaluation of the degree of compensation and the various possible causes of changes, if any. Methods. The participants were 13 regular smokers of commercial or hand-rolled cigarettes. They were tested with four cigarettes, which exhibited a wide range of nicotine to 'tar' ratios at a relatively constant 'tar' yield. Their smoking behaviour was monitored by placing the test cigarettes into an orifice-type holder/flowmeter attached to a custom-built smoker behaviour analyser. In addition, a comprehensive sensory evaluation of the products was carried out. Results. The differences in the nicotine to tar ratios of the samples did not significantly influence the puffing behaviour patterns, i.e. puff number and interval, total and average puff volume, integrated pressure and puff duration. Additionally the pre- to post-exhaled CO boosts were not significantly influenced by the experimental samples used in the study. However, the nicotine yields obtained by the smokers were significantly influenced by the machine-smoked nicotine yields or the nicotine to tar ratios of the samples. The machine-smoked nicotine yields were highly correlated with the nicotine yields obtained under human smoking conditions. For the sensory evaluation, there was only a significant difference between the samples in the intensity of the impact. Conclusion. These observations imply that these puffing variables are not controlled by the nicotine yield of the cigarette.

Can imagined whole-body rotations improve vestibular compensation?

Unilateral damage to the labyrinth and the vestibular nerve cause rotational vertigo, postural imbalance, oculomotor disorders and spatial disorientation. Electrophysiological investigations in animals revealed that such deficits are partly due to imbalanced spontaneous activity and sensitivity to motion in neurons located in the ipsilesional and contralesional vestibular nuclei. Neurophysiological reorganizations taking place in the vestibular nuclei are the basis of the decline of the symptoms over time, a phenomenon known as vestibular compensation. Vestibular compensation is facilitated by motor activity and sensory experience, and current rehabilitation programs favor physical activity during the acute stage of a unilateral vestibular loss. Unfortunately, vestibular-defective patients tend to develop strategies in order to avoid movements causing imbalance and nausea (in particular body movements towards the lesioned side), which impedes vestibular compensation. Neuroanatomical evidence suggests a cortical control of postural and oculomotor reflexes based on corticofugal projections to the vestibular nuclei and, therefore, the possibility to manipulate vestibular functions through top-down mechanisms. Based on evidence from neuroimaging studies showing that imagined whole-body movements can activate part of the vestibular cortex, we propose that mental imagery of whole-body rotations to the lesioned and to the healthy side will help rebalancing the activity in the ipsilesional and contralesional vestibular nuclei. Whether imagined whole-body rotations can improve vestibular compensation could be tested in a randomized controlled study in such patients beneficiating, or not, from a mental imagery training. If validated, this hypothesis will help developing a method contributing to reduce postural instability and falls in vestibular-defective patients. Imagined whole-body rotations thus could provide a simple, safe, home-based and self-administered therapeutic method with the potential to overcome the inconvenience related to physical movements.

Impact Of Chemical Changes On The Sensory Characteristics Of Coffee Beans During Storage.

Sensory changes during the storage of coffee beans occur mainly due to lipid oxidation and are responsible for the loss of commercial value. This work aimed to verify how sensory changes of natural coffee and pulped natural coffee are related to the oxidative processes during 15 months of storage. During this period, changes in the content of free fatty acids (1.4-3.8 mg/g oil), TBARS values (8.8-10.2 nmol MDA/g), and carbonyl groups (2.6-3.5 nmol/mg of protein) occurred. The intensity of rested coffee flavour in the coffee brew increased (2.1-6.7) and 5-caffeoylquinic acid concentration decreased (5.2-4.6g/100g). Losses were also observed in seed viability, colour of the beans and cellular structure. All the results of the chemical analyses are coherent with the oxidative process that occurred in the grains during storage. Therefore, oxidation would be also responsible for the loss of cellular structure, seed viability and sensory changes.

Effect Of Spray Drying On The Sensory And Physical Properties Of Hydrolysed Casein Using Gum Arabic As The Carrier.

This study was aimed at spray drying hydrolysed casein using gum Arabic as the carrier agent, in order to decrease the bitter taste. Three formulations with differing proportions of hydrolysed casein: gum Arabic (10:90, 20:80 and 30:70) were prepared and characterized. They were evaluated for their moisture content, water activity, hygroscopicity, dispersibility in water and in oil, particle size and distribution, particle morphology, thermal behaviour (DSC) and bitter taste by a trained sensory panel using a paired-comparison test (free samples vs. spray dried samples). The proportion of hydrolysed casein did not affect the morphology of the microspheres. The spray drying process increased product stability and modified the dissolution time, but had no effect on the ability of the material to dissolve in either water or oil. The sensory tests showed that the spray drying process using gum Arabic as the carrier was efficient in attenuating or masking the bitter taste of the hydrolysed casein.

Composition, functional properties and sensory characteristics of Mozzarella cheese manufactured from different somatic cell counts in milk

In the present study, composition, functional properties and sensory characteristics of Mozzarella cheese produced from milk with somatic cell counts (SCC) at low (<200,000 cells/mL), intermediate (≈400,000 cells/mL) and high (>800,000 cells/mL) levels were investigated. Three batches of cheese were produced for each SCC category. The cheeses were vacuum packed in plastic bags and analysed after 2, 9, 16, 23 and 30 days of storage at 4ºC. SCC level did not affect the moisture, fat, total protein and ash content, mesophilic and psychrotrophic bacteria, and sensory parameters of Mozzarella cheese. However, meltability increased in cheese manufactured from high SCC milk. Results indicated that raw milk used to produce Mozzarella cheese should not contain high SCC (>800,000 cells/mL) in order to avoid changes in the functional properties of the Mozzarella cheese.

Sensory evaluation of black instant coffee beverage with some volatile compounds present in aromatic oil from roasted coffee

The oil obtained from Brazilian roasted coffee by supercritical CO2 extraction shows considerable aromatic properties, mainly composed by five aromatic compounds, 2-methylpyrazine; 2-furfurylalcohol, 2,5-dimethylpyrazine; γ-butyrolactone and 2-furfurylacetate. Sensory analyses were used to verify the influence of a mixture of these important classes of aromatic coffee compounds (pyrazines, furans and lactones) and of the roasted coffee aromatic oil on the coffee aroma and flavour of black instant freeze and spray-dried coffee beverages. In the acceptance evaluation of the aroma, the samples prepared with freeze-dried instant coffee without the mixture of volatile compounds (sample 4) were not significantly different from the freeze-dried instant coffee in which the aromatic coffee oil was added (sample 5) and from the sample prepared with freeze-dried coffee in which the mixture of the five volatile was added (sample 3), coincidentally from the same drying process. Therefore, sample (3) did not differ from samples prepared with spray dried instant coffee without (sample 1) and to which (sample 2) the mixture of volatile was added. Therefore, with respect to this attribute, the addition of this mixture did not interfere in this drink acceptance. Taking into consideration the flavor, samples prepared with freeze-dried instant coffee in which the aromatic coffee oil was added (5) and the samples with (3) and without (4) the mixture of the five volatile was added did not differ significantly, however sample (4) did not differ from samples (1) and (2). Regarding this attribute, the addition of the aromatic oil of roasted coffee or a mixture of volatile in samples of freeze-dried instant coffee had a better acceptance than those dried by spray dryer (1) and (2). Thus, the enrichment of drinks with the aromatic oil of roasted coffee, or even with the mixture of the five components did not influence the consumer acceptance with respect to the aroma, but exerts influence with respect to flavour.

Spectroscopic characterization and investigation of the dynamic of charge compensation process of supramolecular films derived from tetra-2-pyridyl-1,4-pyrazine ligand

This work describes the infrared spectroscopy characterization and the charge compensation dynamics in supramolecular film FeTPPZFeCN derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) with hexacyanoferrate, as well as the hybrid film formed by FeTPPZFeCN and polypyrrole (PPy). For supramolecular film, it was found that anion flux is greater in a K+ containing solution than in Li+ solution, which seems to be due to the larger crystalline ionic radius of K+. The electroneutralization process is discussed in terms of electrostatic interactions between cations and metallic centers in the hosting matrix. The nature of the charge compensation process differs from others modified electrodes based on Prussian blue films, where only cations such as K+ participate in the electroneutralization process. In the case of FeTPPZFeCN/PPy hybrid film, the magnitude of the anions’s flux is also dependent on the identity of the anion of the supporting electrolyte.

Sensory analysis of hydrolysed meat preparations

A utilização de hidrolisados de carne em dietas melhora seu conteúdo protéico, de vitaminas e minerais. O objetivo do presente trabalho foi avaliar a aceitação de hidrolisados de carne. Quatro preparações foram desenvolvidas com três tipos de hidrolisados em condições similares às domésticas. . A aceitação foi avaliada com uso de escala hedônica de 9 pontos. Os testes foram realizados em três sessões (de acordo com o tipo de hidrolisado) e, incluiu-se na ficha de avaliação informações de idade. A análise estatística foi realizada por ANOVA e teste de Tukey. As preparações mais aceitas foram os bolinhos com hidrolisados de peru e frango. Os hidrolisados podem ser utilizados em diversas preparações, sendo necessário o conhecimento da faixa etária a qual se destinam, suas características sensoriais e físico-químicas, para garantir o sabor e a aparência do produto final