Chemosensory Loss during a Traumatic Brain Injury Suggests a Central Pathway for the Rehabilitation of Anosmia.

Currently, no method has been developed for rehabilitating olfaction in anosmic patients following a traumatic brain injury (TBI). Here a method for rehabilitation is described which is based on a recent finding that the human posterior pyriform cortex (PPC) generates predictive odor "search images" in advance of an encounter with an olfactory stimulus. The search image enhances perceptual sensitivity and allows the odor it represents to be identified without input occurring from the olfactory receptors or bulbs. Furthermore, based on the finding here that anosmics with a TBI often have normal trigeminal and gustatory function, it is proposed that normality in these chemosensory systems may indicate that key cortical regions including the PPC are intact in anosmics and capable of processing olfactory information. In addition, the results of chemosensory tests of the olfactory, gustatory, and intranasal trigeminal systems of 18 patients with a TBI are given that identify which patients would most likely benefit from the rehabilitation procedure.

Taste-Elicited Activity in Facial Muscle Regions in 5-8-Week-Old Infants.

The state of development of the sense of taste in humans during the first few months of life is only partially understood. Since taste plays a critical role in the feeding and nutrition of infants a better understanding of taste development during early life is required. Currently, information about the sense of taste in pre-verbal infants is obtained by analysis of videotaped facial expressions using the Baby FACS coding system. A potentially more objective faster procedure for assessing facial expressions not investigated in infants is electromyography (EMG). The method has been successfully used to study taste-elicited responses in the mid-face muscle regions of the levator labii and zygomaticus major of 6-9-year-olds and in a range of facial muscle regions in adults. Accordingly, this study aimed to investigate taste in young infants using EMG to 1) measure activity simultaneously in 4 facial muscle regions in response to 3 common tastants and 2) determine whether the activities of one or more muscle regions is needed to provide evidence of perception of a tastant by an infant. The results indicated that multiple facial muscle regions responded simultaneously but differentially to non-sweet and sweet tastants and recordings of activities from 3 or 4 regions simultaneously indicated that almost 100% of infants responded to the unpleasant tastes of quinine and citric acid, and 80% to sucrose.

Reduced taste function and taste papillae density in children with chronic kidney disease.

BACKGROUND: Taste loss may contribute to the loss of appetite in children with chronic kidney disease (CKD) and other serious medical conditions that result in malnutrition. Traditional methods for measurement of taste loss commonly use aqueous tastant solutions that can induce nausea, vomiting, or even pain in the mouth. An alternative is to measure fungiform papillae density on the anterior tongue since this correlates with taste sensitivity. Here we aimed to develop a non-invasive method for assessing papillae density on the anterior tongue and to use the method to determine if CKD patients [estimated glomerular filtrate (eGFR < 60 ml/min/1.73 m(2))] have a lower density than clinical controls (CC)(eGFR > 89 ml/min/1.73 m(2)). METHODS: Thirty-five healthy adults participated in the development of a method, which was assessed by 24 children, 12 of whom were CKD patients and 12 were clinical controls. RESULTS: Similar papillae densities were found using invasive and non-invasive methods (F(1,34) = 0.647, p = 0.427). The CKD group had a significantly lower papillae density (X(2) = 7.17, p = 0.007) and poorer taste sensitivity than the CC group (p = 0.0272), and the density correlated significantly with eGFR (r = 0.56, p < 0.01). CONCLUSIONS: Loss of taste in children with CKD is due to the reduced number of papillae and their taste-sensing receptor cells.

Changes in fungiform papillae density during development in humans.

The anterior region of the human tongue ceases to grow by 8-10 years of age and the posterior region at 15-16 years. This study was conducted with 30 adults and 85 children (7-12 year olds) to determine whether the cessation of growth in the anterior tongue coincides with the stabilization of the number and distribution of fungiform papillae (FP) on this region of the tongue. This is important for understanding when the human sense of taste becomes adult in function. This study also aimed to determine whether a small subpopulation of papillae could be used to predict the total number of papillae. FP were photographed and analyzed using a digital camera. The results indicated that the number of papillae stabilized at 9-10 years of age, whereas the distribution and growth of papillae stabilized at 11-12 years of age. One subpopulation of papillae predicted the density of papillae on the whole anterior tongue of 7-10 year olds, whereas another was the best predictor for the older children and adults. Overall, the population, size, and distribution of FP stabilized by 11-12 years of age, which is very close to the age that cessation of growth of the anterior tongue occurs.

Chemosensory function and food preferences of children with cystic fibrosis.

A major problem for patients with cystic fibrosis (CF) is the maintenance of adequate nutrition to maintain normal growth. The hypotheses that poor nutrition could be due to smell and/or taste dysfunction has been pursued in several studies with contradictory results. None, however, investigated whether inadequate nutrition is due to CF patients having different liking for foods compared to healthy children and whether liking can be linked to specific changes in smell or taste function. Here, the relationships between food liking, BMI, and smell and taste function in 42 CF and 42 healthy 5- to 18-year olds is pursued. A three-choice 16-item odor identification test and a gustatory identification test involving five concentrations of sweet, sour, bitter, and salty tastes, were used to assess chemosensory function. Food liking was assessed using a 94-item questionnaire. Patients identified significantly fewer odors than controls (89.8% vs. 95.7% correct; P < 0.001). However, only a few patients were affected and their loss of olfactory function was not substantial and unlikely to affect their liking for foods. Taste identification was similar for the two groups (patients 92.6% vs. controls 94.2% correct). There was no correlation between age and odor identification ability, but taste performance improved with age (r = 0.39, P < 0.05), suggesting cognition was the cause. Patients liked several types of foods and high-fat foods more than the controls. Both groups had a similar liking for low-fat foods and both liked high-fat foods more than low-fat foods. No significant relationships existed between FEV(1) and smell or taste function or liking for foods, the BMI of the groups were similar and there was no relationship between BMI and smell or taste function. The results indicate that the abnormal eating behavior reported for many CF patients is not due to changes in chemosensory function which remains normal in most CF patients at least to 18 years of age.

Temporal processing of olfactory stimuli during retronasal perception.

Odorants can be perceived via the nose during an inhalation or sniff (orthonasal perception) and via the mouth, nasopharynx and nasal cavity during mastication or drinking (retronasal perception). Previous data suggest that orthonasal perception provides a more efficient route with greater difficulty being reported when detecting [Halpern BP. Retronasal and orthonasal smelling. Chemosense 2004;6:1-7; Voirol E, Daget N. Comparative study of nasal and retronasal olfactory perception. Lebensmittel-Wissenschaft Technol 1986;19:316-9] and identifying [Heilmann S, Hummel T. A new method for comparing orthonasal and retronasal olfaction. Behav Neurosci 2004;118:412-9; Sun BC, Halpern BP. Identification of air-phase retronasal and orthonasal odorant pairs. Chem Senses 2005;30:1-14] single odorants retronasally. Whether the poorer sensitivity obtained via the retronasal route is largely due to the greater adsorption of odorants by the nasopharyngeal mucus compared to the nasal mucus thereby reducing their peak concentration and/or slowing their passage, has not been resolved. Importantly, the question of whether solubility of odorants in mucus or water predicts the outcomes for perception of stimuli presented via the retronasal route has not been resolved. Accordingly, the present study investigates this question by determining whether the solubility of an odorant in mucus predicts which component of a binary odour mixture is perceived first during retronasal perception. The results indicate that solubility in mucus rather than solubility in water is a better predictor of which odour will be perceived first and identified more readily during the retronasal perception of a binary mixture. In addition, lower intensity levels of single odorants occurred via the retronasal route suggesting that adsorption was greater via this route. Whether this was due to nasopharyngeal mucus having a greater adsorptive area or different composition compared to the orthonasal pathway is not known.

Facial electromyography: responses of children to odor and taste stimuli.

The study investigated the potential for facial electromyography (EMG) to be used as a clinical tool for measuring the responses of children to pleasant and unpleasant smell and taste stimuli. Responses in the zygomaticus major and levator labii muscles to 4 odorants and 4 tastants were recorded from 34 children aged 6-9 years. The results indicated that EMG activities in the 2 muscles discriminated between pleasant and unpleasant stimuli within each modality in a manner that indicated that the children perceived the hedonic qualities of the stimuli in a manner similar to that reported for adults. Importantly, there was unanimous agreement across the children as regards the differential nature of the activities exhibited. These outcomes together with the results of earlier facial expression studies suggest that facial EMG may provide an objective procedure that could be suitable for the clinical assessment of taste and smell function in newborns and young infants.

Rapid quantitative assessment of fungiform papillae density in the human tongue.

Fungiform papillae density, which can be used in a variety of circumstances as an indicator of taste function [L.M. Bartoshuk, V.B. Duffy, I.J. Miller, PTC/PROP tasting: anatomy, psychophysics and sex effects, Physiol. Behav. 56 (1994) 1165-1171; I.J. Miller, F.E. Reedy, Variation in human taste bud density and taste intensity perception, Physiol. Behav. 47 (1990) 1213-1219; J.R. Zuniga, N. Chen, C.L. Phillips, Chemosensory and somatosensory regeneration after lingual nerve repair in humans, J. Oral Maxillofac. Surg. 55 (1997) 2-13], was measured on the dorsal surface of the anterior tongue of living humans using a digital camera and a videomicroscope. Both procedures provided similar results, with the camera providing a more rapid, portable and flexible imaging procedure. Subsequently, the camera was successfully used to identify small regions of the anterior tongue which provide reliable measures of fungiform papillae density that correlate highly with the total number of fungiform papillae on the anterior tongue.

Perception of temporal order and the identification of components in taste mixtures.

The capacity of humans to identify the components of taste mixtures is limited to 3 for most people [D.G. Laing, C. Link, A. Jinks, I. Hutchinson, The limited capacity of humans to identify the components of taste mixtures and taste-odor mixtures. Perception 31 (2002) 617-635]. Here, the hypothesis that temporal processing differences have a major role in limiting capacity is investigated. Thirty two subjects were trained to identify sucrose, sodium chloride and citric acid at FIVE concentration levels and were then required to indicate (1) which tastant was perceived first and (2) the identity of each component, in binary and ternary mixtures. Within each mixture set, e.g. sucrose-citric acid, the concentrations of components were adjusted to provide some conditions where intensities and time differences in processing the individual components were minimized. With binary mixtures, changes in intensity resulted in identification of only one component when the differences were largest, and both being identified when intensities were similar. In contrast, subjects found it difficult to indicate which component was perceived first when the intensities were similar and easy when they were substantially different. The most profound effects occurred with ternary mixtures. With each of the three sets, there were several where subjects could not indicate which component was perceived first, and in 13/18 mixtures not all components were identified above chance. Indeed, the most common number of components identified was 2. However, although perception of order was lost in a number of mixtures, this did not preclude identification of one or all three components. This result contrasts with the finding with odors where total loss of order resulted in loss of identity of all components in ternary mixtures [A. Jinks, D.G. Laing, Temporal processing reveals a mechanism for limiting the capacity of humans to analyze mixtures. Cognitive Brain Res. 8 (1999) 311-325]. Thus, loss of identity with taste mixtures seems to occur to a lesser degree. Indeed suppression rather than temporal effects may be the main cause of the loss of identity of components with ternary taste mixtures.

A quantitative study of fungiform papillae and taste pore density in adults and children.

Male children (8-9 years) are reported to have a higher sensitivity than male adults to the sweet tastant sucrose when small regions of the anterior tongue are stimulated. The present study investigated the hypothesis that the higher sensitivity was due to a greater density of fungiform papillae and taste pores (buds), since it has been reported in adults that increased densities of these two structures correlates with increased taste suprathreshold sensitivity [Physiol. Behav. 47 (1990) 1213]. Quantitative measures of the number and size of papillae and pores in two areas of the tongue that had been shown to have a higher sensitivity for sucrose were achieved in 20 male children 8-9 years of age and 20 adults 18-30 years of age, using videomicroscopy and NIH Image software. Customized templates and a red food dye were used to define the equivalent tongue locations across the 40 subjects and taste pores were stained with methylene blue. Children were found to have substantially smaller papillae than adults but significantly higher papilla densities in both areas. Similar numbers of taste pores per papilla were found for both groups, resulting in children having much higher taste pore densities in each area than adults. Other differences included smaller taste pore diameters in children compared to adults, and the papillae tended to be rounder in children. Overall, the results support the hypothesis that the higher densities of fungiform papillae and taste pores in children underlie their greater sensitivity for sucrose in the two areas. In addition, the anatomical differences between adults and children indicate the sense of taste is in a state of development during mid-childhood.

Temporal perception of sweetness by adults and children using computerized time-intensity measures.

There is a general paucity of knowledge of the cognitive and perceptual abilities of children to successfully undertake chemosensory-related tasks. An example is that there are no reports of temporal perception by children in time-intensity tasks, or how their responses in these tasks compare with those of adults. The latter paradigm has the potential to reveal differences that may occur during a normal eating or drinking episode that cannot be detected with single response measures. To address this shortcoming, the present study uses a computerized time-intensity method to compare the responses of adults and 8- to 9-year-olds in several measures of sweetness with three different types of stimuli. The results show that the children gave higher estimates than adults of the maximum sweetness of sucrose in water, orange drink and custard and recorded shorter sweetness durations with orange drink and custard. Both age groups, however, responded similarly to changes in concentration and the volume of stimuli with all three sensory measures. Overall, the consistency of the data from the children and the variability, which was similar to that of the adults, indicate that the tasks involved in the time-intensity paradigm were within the cognitive ability of the children. Nevertheless, further studies are needed to determine the basis of the differences found.

The limited capacity of humans to identify the components of taste mixtures and taste-odour mixtures.

The capacity of humans to identify the components of taste mixtures and odour-taste mixtures was investigated in two experiments. Subjects were trained to identify the components presented alone and to use a 'yes/no' procedure to identify them in mixtures. All stimuli were presented with a retronasal (by mouth) technique. A maximum of three tastants were identified in both types of mixtures, only one tastant was identified in five-component taste mixtures, and no component was identified in four-component odour-taste mixtures. Importantly, in no instance was the olfactory stimulus identified in any mixture with tastes, including binary mixtures. Loss of identity of the odorant in binary and ternary mixtures may have been due to suppression as a consequence of temporal processing, or to the absence of an association between the odorant and tastants that had established an identifiable percept. In contrast, poor identification of the components of the quaternary odour-taste mixture and quinternary taste mixture is attributed to the limited capacity of working memory. Overall, the poorer ability to identify components in odour-taste mixtures than in taste mixtures indicates that interactions occurred between the two senses, challenging the proposal that odours and tastes are processed independently when present in complex chemosensory stimuli.

Taste development: differential growth rates of tongue regions in humans.

There is a paucity of information about the anatomical and functional development of the human gustatory system. Although the anatomical development of the taste-sensitive fungiform, circumvallate and foliate papillae in the respective anterior, posterior and latero-posterior regions of the dorsal surface of the tongue has been well documented in the fetus, there is limited information about how these regions grow and when they exhibit adult function. The present study is concerned with determining when the growth of one of these taste-sensitive regions becomes adult in size, namely, the anterior region, and how this growth compares with that of the remaining posterior region. Two-hundred and thirty-two living subjects aged between 4 and 32 years participated. Following the identification and marking of a series of landmarks on the dorsal surface of the tongue with blue food dye, five measurements of the width and length of various parts of the tongue allowed calculation of the growth of the anterior and posterior regions. The results indicate that the fungiform papillae-rich anterior region attains adult-size by 8-10 years of age whilst the posterior region continues to grow until 15-16 years. Interestingly, this early development is not matched by achievement of adult function [Dev. Brain Res. 82 (1994) 286] or adult size papillae or taste pores [Dev. Brain Res., submitted]. Finally, the findings of the present study will allow studies of the development of taste function in humans to be conducted using equivalent tongue areas in subjects of different ages.