Neural Coding of Food Is a Multisensory, Sensorimotor Function

Electrophysiological responses to appetitive and consummatory behavior in the rostral nucleus tractus solitarius in awake, unrestrained rats

Introduction

As the intermediate nucleus in the brainstem receiving information from the tongue and transmitting information upstream, the rostral portion of the nucleus tractus solitarius (rNTS) is most often described as a "taste relay". Although recent evidence implicates the caudal NTS in a broad neural circuit involved in regulating ingestion, there is little information about how cells in the rNTS respond when an animal is eating solid food.

Methods

Single cells in the rNTS were recorded in awake, unrestrained rats as they explored and ate solid foods (Eating paradigm) chosen to correspond to the basic taste qualities: milk chocolate for sweet, salted peanuts for salty, Granny Smith apples for sour and broccoli for bitter. A subset of cells was also recorded as the animal licked exemplars of the five basic taste qualities: sucrose, NaCl, citric acid, quinine and MSG (Lick paradigm).

Results

Most cells were excited by exploration of a food-filled well, sometimes responding prior to contact with the food. In contrast, cells that were excited by food well exploration became significantly less active while the animal was eating the food. Most cells were broadly tuned across foods, and those cells that were recorded in both the Lick and Eating paradigms showed little correspondence in their tuning across paradigms.

Discussion

The preponderance of robust responses to the appetitive versus the consummatory phase of ingestion suggests that multimodal convergence onto cells in the rNTS may be used in decision making about ingestion.

Electrophysiological responses to appetitive and consummatory behavior in the rostral nucleus tractus solitarius in awake, unrestrained rats

As the intermediate nucleus in the brainstem receiving information from the tongue and transmitting information upstream, the rostral portion of the nucleus tractus solitarius (rNTS) is most often described as a "taste relay". Although recent evidence implicates the NTS in a broad neural circuit involved in regulating ingestion, there is little information about how cells in this structure respond when an animal is eating solid food. Here, single cells in the rNTS were recorded in awake, unrestrained rats as they explored and ate solid foods (Eating paradigm) chosen to correspond to the basic taste qualities: milk chocolate for sweet, salted peanuts for salty, Granny Smith apples for sour and broccoli for bitter. A subset of cells was also recorded as the animal licked exemplars of the five basic taste qualities: sucrose, NaCl, citric acid, quinine and MSG (Lick paradigm). Results showed that most cells were excited by exploration of a food-filled well, sometimes responding prior to contact with the food. In contrast, cells that were excited by food well exploration became significantly less active while the animal was eating the food. Most cells were broadly tuned across foods, and those cells that were recorded in both the Lick and Eating paradigms showed little correspondence in their tuning across paradigms. The preponderance of robust responses to the appetitive versus the consummatory phase of ingestion suggests that multimodal convergence onto cells in the rNTS may be used in decision making about ingestion.

Neurosensory development of the four brainstem-projecting sensory systems and their integration in the telencephalon

Somatosensory, taste, vestibular, and auditory information is first processed in the brainstem. From the brainstem, the respective information is relayed to specific regions within the cortex, where these inputs are further processed and integrated with other sensory systems to provide a comprehensive sensory experience. We provide the organization, genetics, and various neuronal connections of four sensory systems: trigeminal, taste, vestibular, and auditory systems. The development of trigeminal fibers is comparable to many sensory systems, for they project mostly contralaterally from the brainstem or spinal cord to the telencephalon. Taste bud information is primarily projected ipsilaterally through the thalamus to reach the insula. The vestibular fibers develop bilateral connections that eventually reach multiple areas of the cortex to provide a complex map. The auditory fibers project in a tonotopic contour to the auditory cortex. The spatial and tonotopic organization of trigeminal and auditory neuron projections are distinct from the taste and vestibular systems. The individual sensory projections within the cortex provide multi-sensory integration in the telencephalon that depends on context-dependent tertiary connections to integrate other cortical sensory systems across the four modalities.

Individual characteristics, including olfactory efficiency, age, body mass index, smoking and the sex hormones status, and food preferences of women in Poland

Background

Food choices made by most people mainly depend on food preferences. Knowing how certain factors affect food preferences can help dietitians working with women to understand the relationship between individual factors and the challenges faced by the women in changing eating habits. The aim of the study was to examine the food preferences of women and to assess the impact of the sense of smell, age, body mass index (BMI), smoking and hormonal status (phase of the menstrual cycle, hormonal contraception) on the declared pleasure derived from eating various types of food.

Methods

A total of 190 women living in the Górnośląsko-Zagłębiowska Metropolis in Poland aged 18-75 (19.29-26.71 RNO) years participated in the study. The collected survey data included age, BMI, smoking, phase of the menstrual cycle and hormonal contraception. Olfactory sensitivity was measured by T08 olfactometer. Additionally, food preferences were assessed, using 24 different food types, which were presented as pictures. To evaluate food preferences 10 cm visual analogue scale was used.

Results

The most liked foods were: fruits (M = 8.81, SD = 1.67), sweet desserts (M = 8.44, SD = 2.30), vegetables and salads (M = 8.08, SD = 2.24), chocolate (M = 7.84, SD = 2.76), and poultry (M = 7.30, SD = 2.47). The least liked foods were: salty products (M = 4.98, SD = 3.03), milk soup (M = 3.30, SD = 3.13), and seafood (M = 2.99, SD = 3.28). The influence of the analyzed factors on the degree of liking six food types was shown. Women with better ability to name scents preferred sausages/ham and beef/pork. Women with a higher BMI had lower preference for jellybeans and broth. Women who were heavier smokers had lower preference for milk soup. In women using hormonal contraception, pleasure from eating sausages and ham was higher than compared to women in all phases of the monthly cycle. In women in the follicular phase the pleasure from eating pasta was lower when compared to women in the ovulatory phase, the luteal phase and those using hormonal contraception. In women in the ovulatory phase the pleasure from eating candies and jellybeans was lower when compared to women in the follicular phase, the luteal phase and those using hormonal contraception. In women in the ovulatory phase, also pleasure from eating broth was lower when compared to women in the luteal phase and those using hormonal contraception.

Conclusions

Among women in Poland, the top five preferred food types are fruits, sweet desserts, vegetables/salads, chocolate and poultry. To confirm the extent to which the declared pleasure derived from eating these food types translates into health condition, further research on the consumption of these food types is necessary. The impact of the sense of smell, BMI, smoking, or menstrual cycle phase and hormonal contraception on the declared pleasure derived from eating was observed for six out of twenty-four food types. The hormonal status was the factor most significantly influencing food preferences.

Augmented reality flavor: cross-modal mapping across gustation, olfaction, and vision

Gustatory display research is still in its infancy despite being one of the essential everyday senses that human practice while eating and drinking. Indeed, the most important and frequent tasks that our brain deals with every day are foraging and feeding. The recent studies by psychologists and cognitive neuroscientist revealed how complex multisensory rely on the integration of cues from all the human senses in any flavor experiences. The perception of flavor is multisensory and involves combinations of gustatory and olfactory stimuli. The cross-modal mapping between these modalities needs to be more explored in the virtual environment and simulation, especially in liquid food. In this paper, we present a customized wearable Augmented Reality (AR) system and olfaction display to study the effect of vision and olfaction on the gustatory sense. A user experiment and extensive analysis conducted to study the influence of each stimulus on the overall flavor, including other factors like age, previous experience in Virtual Reality (VR)/AR, and beverage consumption. The result showed that smell contributes strongly to the flavor with less contribution to the vision. However, the combination of these stimuli can deliver richer experience and a higher belief rate. Beverage consumption had a significant effect on the flavor belief rate. Experience is correlated with stimulus and age is correlated with belief rate, and both indirectly affected the belief rate.

Does Each Menstrual Cycle Elicit a Distinct Effect on Olfactory and Gustatory Perception?

The obesity pandemic has brought forth a scientific interest in food intake and sensory perception interactions. Olfactory perception and gustatory perception are very complex and under the influence of many factors, including the menstrual cycle. This study aims to clarify conflicting findings on the influence of the menstrual cycle on olfactory and gustatory perception. Women were assessed during four consecutive phases of one complete cycle (mid-follicular, ovulatory, mid-luteal, and late luteal phases (N = 21)), in contrast to women measured across the same phases belonging to two menstrual cycles (N = 29). Additional control groups were men (N = 17), postmenopausal women (N = 14), oral contraceptive users (N = 10), and women with an anovulatory cycle (N = 8). Olfactory threshold, odor discrimination, and identification were tested using the "Sniffin Sticks" test kit. Suprathreshold intensity and hedonic ratings for sweet, salty, sour, and bitter solutions were assessed. One-way ANOVA and ANOVA for repeated measurements was applied in the analysis, along with linear and trigonometric data fitting and linear mixed models. Linear increases in olfactory discrimination, identification, and overall olfactory performance were observed only in women followed across a complete menstrual cycle. Compared to other groups, these women displayed a cyclic pattern characterized by a predilection for sweet solution; reduced distaste for salty and sour solutions; and increased intensity perception of salty, sour, and bitter solutions towards the end of the cycle. These results suggest that a distinct hormonal milieu of a complete menstrual cycle may be affecting both olfactory and gustatory perception.