Orthonasal Stimulation Research Articles

Differences in olfactory bulb mitral cell spiking with ortho- and retronasal stimulation revealed by data-driven models.

The majority of olfaction studies focus on orthonasal stimulation where odors enter via the front nasal cavity, while retronasal olfaction, where odors enter the rear of the nasal cavity during feeding, is understudied. The coding of retronasal odors via coordinated spiking of neurons in the olfactory bulb (OB) is largely unknown despite evidence that higher level processing is different than orthonasal. To this end, we use multi-electrode array in vivo recordings of rat OB mitral cells (MC) in response to a food odor with both modes of stimulation, and find significant differences in evoked firing rates and spike count covariances (i.e., noise correlations). Differences in spiking activity often have implications for sensory coding, thus we develop a single-compartment biophysical OB model that is able to reproduce key properties of important OB cell types. Prior experiments in olfactory receptor neurons (ORN) showed retro stimulation yields slower and spatially smaller ORN inputs than with ortho, yet whether this is consequential for OB activity remains unknown. Indeed with these specifications for ORN inputs, our OB model captures the salient trends in our OB data. We also analyze how first and second order ORN input statistics dynamically transfer to MC spiking statistics with a phenomenological linear-nonlinear filter model, and find that retro inputs result in larger linear filters than ortho inputs. Finally, our models show that the temporal profile of ORN is crucial for capturing our data and is thus a distinguishing feature between ortho and retro stimulation, even at the OB. Using data-driven modeling, we detail how ORN inputs result in differences in OB dynamics and MC spiking statistics. These differences may ultimately shape how ortho and retro odors are coded.

Investigating the oronasal contributions to metallic perception

AbstractMetallic taints elicited when consuming food can be unpleasant for the consumer and are therefore problematic to food manufacturers. Although metallic has been proposed as a taste in the past, evidence remains inconclusive. This study investigates the oral and nasal contributions to metallic perception using sensory evaluation and headspace analysis using gas chromatography–mass spectrometry (GC‐MS). When sniffing the headspace over divalent salt solutions, some were discriminated from water. GC‐MS did not detect volatiles in the sample headspace, one hypothesis being that sample volatiles react with phospholipids in the nasal cavity and it is lipid oxidation products which are perceived. Copper sulphate was reported as metallic when tasted with the nose occluded to eliminate retronasal perception, suggesting a gustatory or trigeminal mechanism may be involved. This work indicates orthonasal stimulation is involved in metallic perception, and contributes to the ongoing debate over metallic being a taste, trigeminal or flavour response.

Swallowing Is Differentially Influenced by Retronasal Compared with Orthonasal Stimulation in Combination with Gustatory Stimuli

Identical stimuli are processed differently when presented ortho- or retronasally. In contrast to orthonasal olfaction, retronasal odorant perception is strongly associated with flavor and food intake, which is usually followed by swallowing. Along with other stimuli, gustatory stimuli are known to influence the swallowing reflex. It was therefore the aim of present study to examine whether retronasal olfaction, in combination with simultaneous gustatory stimuli, influences swallowing in a manner different from that of orthonasal olfaction. Fifty normosmic and normogeusic subjects took part in the study. A sweet taste (glucose, delivered via an intraoral taste dispenser) was presented simultaneously with vanillin, a food-like odor, either ortho- or retronasally at random using a computer-controlled olfactometer. Ultrasound imaging of the mouth floor was recorded on videotape to continuously monitor swallowing activity. After retronasal stimulation, swallowing occurred significantly faster (7.49 vs. 9.42 s; P < 0.001) and also took place more frequently compared with swallowing after orthonasal stimulation (1.38 times vs. 1.14 times; P < 0.001). These results show that a food-like odorant presented retronasally in combination with a congruent taste stimulus can influence swallowing. Whether these results can be assigned to other, unfamiliar, unpleasant nonfood-like odors has yet to be determined.

Influence of simultaneous gustatory stimuli on orthonasal and retronasal olfaction

Orthonasal and retronasal olfaction processes differ. The aim of this study was to examine whether congruent and incongruent simultaneous gustatory stimuli influence orthonasal and retronasal odorant perception, using olfactory event-related potentials as a measure. Thirty-two young, healthy subjects (16 men, 16 women) took part in two test sessions. Olfactory event-related potentials were recorded in response to a food-like odor, vanillin, and to an odor usually not associated with foods, the rose-like phenylethylalcohol. Each session consisted of four randomized blocks of 15 stimuli each which were applied either orthonasally or retronasally. Simultaneously, sweet or sour gustatory stimuli were applied. In response to retronasal vanillin, stimuli latencies P2 of the event-related potentials were significantly shorter in the congruent “sweet condition” than the incongruent “sour condition”. In contrast, with orthonasal stimulation, shorter P2 latencies were seen for both odorants in the incongruent condition. Intensity of both odorants was perceived as less pronounced after retronasal stimulation than after orthonasal stimulation. In conclusion, application of a sweet taste significantly enhanced the processing of a congruent olfactory stimulus when presented through the retronasal route. Incongruent simultaneous gustatory stimulation applied during orthonasal olfaction seemed to induce conflict priming, also resulting in faster processing.

Synergy and Masking in Odor Mixtures: An Electrophysiological Study of Orthonasal vs. Retronasal Perception

Perceptual interactions in a model of wine woody-fruity binary mixtures were previously reported in a psychophysical study performed through orthonasal stimulation only. However, recent studies suggested that the perception of food-like and nonfood-like odors may depend on the route of stimulation. The aim of the present study was two-fold: first to examine the neural correlates of perceptual interactions using electroencephalogram (EEG)-derived event-related potentials (ERPs) and second to test the influence of the stimulation route on quality perception. Therefore, we designed an experiment with 30 subjects to study perceptual interactions in woody-fruity mixtures and compared ortho- vs. retronasal stimulation sites on perceived odor quality and ERPs. The results revealed synergy or masking of the fruity component, depending on the woody component level. Synergy was supported by larger N1 amplitude of the ERP. Furthermore, mixtures including a medium level of the woody odor elicited a strong increase of P2 amplitude only retronasally. This study evidenced for the first time electrophysiological correlates of both perceptual synergy and masking on the early component of the ERPs and confirmed that retro- vs. orthonasal stimulation route induces different neural processes that are reflected in the late component of the ERP.

Olfactory event-related potentials in response to ortho- and retronasal stimulation with odors related or unrelated to foods

The aim of this study was to investigate the perception of odor intensity following ortho- and retronasal odor presentation and to simultaneously study differences between ortho- and retronasal olfaction using an electrophysiological measure event-related potentials (ERP). Using air-dilution olfactometry, 24 young healthy subjects were investigated. For retro- and orthonasal stimulation, a technique was used that allowed precise control of stimulus characteristics. To investigate potential distinctions between the processing of food and non-food related odors, lavender and chocolate odors were used. Results indicated that, when an odor unrelated to food was presented in an unusual site, i.e., retronasally, the response was larger compared with presentation of the same odor at an orthonasal site. This was the other way around for a food-related odor. These changes indicate differences of information processing depending on the context and the route of odor presentation which has direct implications for the enjoyment of foods and drinks.

Importance of retronasal and orthonasal olfaction for odor aversion memory in rats.

The role of odors in food memory formation, especially for aversions, has long been considered secondary to taste. However, the importance of odor ingestion in conditioned odor aversion (COA) has recently challenged this assumption (B. M. Slotnick, F. Westbrook, & F. M. C. Darling, 1997). The aim of the present study was to evaluate the respective role of orthonasal and retronasal olfactory experience in COA acquisition, long-term retention, extinction, and spontaneous recovery. To this end, the odor was presented either close to the drinking spout (orthonasal stimulation) or close to and mixed with the drinking water (eliciting both orthonasal and retronasal stimulation). The authors brought evidence that odor ingestion was crucial for COA acquisition, especially when odor presentation and gastric malaise were separated by long delays. On the contrary, once formed, a distal (orthonasal) odor recognition was sufficient for COA to be retrieved. COA was odor specific and long lasting (more than 50 days). Moreover, results brought evidence for a spontaneous recovery of odor aversion tested 57 days after its extinction.

Cross-Modality of Texture and Aroma Perception Is Independent of Orthonasal or Retronasal Stimulation

To assess the influence of orthonasal and retronasal stimulation on cross-modal interactions between texture and flavor perception of food, a series of experiments have been conducted. Healthy human subjects were exposed to strawberry aroma pulses delivered by a computer-controlled stimulator based on air dilution olfactometry. Just prior to exposure to the aroma, the human subjects consumed water, custard, or protein gels with different textures without any added aroma. The aroma was delivered as a sequence of aroma pulses, in either an orthonasal or a retronasal fashion. The retronasal presentation of aroma with concomitant presentation of texture is thought to more closely mimick the in vivo flavor release of semisolid food products as compared to orthonasal stimulation. The time between oral consumption of the food, including swallowing, and the exposure to the aroma varied between 0.5 and 6.5 s. The subjects rated the intensity of the strawberry aroma. It was observed that the intensity of aroma decreased with increasing firmness of the food that was consumed. Aroma pulses delivered 6.5 s after swallowing were perceived as being more intense as compared to aroma pulses delivered immediately after swallowing. In conjunction with late delivery, the effect cross-modal interactions apparently decreased. Significantly higher odor intensities were reported for the aroma stimuli supplied orthonasally in comparison to retronasal administration. The observed cross-modal effect of texture on aroma intensity was not significantly altered by the mode of aroma delivery, i.e., orthonasal or retronasal stimulus administration.

Differences Between Orthonasal and Retronasal Olfactory Functions in Patients With Loss of the Sense of Smell

To investigate differences between orthonasal and retronasal olfaction in patients with loss of the sense of smell without taste complaints. Electrophysiological and psychophysical testing of orthonasal and retronasal olfactory functions. Outpatient clinics. A series of 18 patients who had olfactory loss due to various reasons but no "taste" complaints. Orthonasal and retronasal olfactory functions assessed by olfactory event-related potentials and psychophysical smell tests. Psychophysical testing revealed retronasal olfaction to be normal or slightly altered, whereas orthonasal olfaction was either absent or severely compromised. Findings from nasal endoscopic examinations and computed tomographic scans were within the reference range in all subjects. In response to orthonasal stimulation there were neither detectable olfactory event-related potentials nor any with small amplitudes, whereas olfactory event-related potentials in response to retronasal stimulation were clearly present in some patients. These clinical observations, together with the psychophysical and electrophysiological findings, suggest that orthonasal and retronasal olfaction might be processed differently.

Enhancement of sweetness ratings of aspartame by a vanilla odor presented either by orthonasal or retronasal routes.

When taste stimuli are presented with specific odor stimuli, the perceived intensity of taste is enhanced, a phenomenon called odor-induced taste enhancement. There is a possibility, however, that the odor substances might have stimulated the taste receptors in the oral cavity as well as odor receptors in the nasal cavity because the odor substances were dissolved in the taste solutions in some preceding studies. Schifferstein and Verlegh (1996) found that the odor-induced taste enhancement effect was not found when the subjects wore a nose clip to prevent the olfactory perception. Thus, it was suggested that the odor-induced taste enhancement did not result from the stimulation of receptors in the oral cavity. To confirm and extend their study, we presented the odor stimuli simultaneously with, but not dissolved in, the taste stimuli with a more advanced approach to stimulus presentation. The participants reported enhancement of sweetness ratings for aspartame when the taste stimuli were presented with a vanilla odor. This odor induced taste enhancement was found when the gaseous odor stimuli were presented either by the retronasal route or by the orthonasal route. There was little possibility that the vanilla odor stimulated the taste receptors during the orthonasal stimulation because the odor stimuli were presented directly into the nasal cavity. Thus, we could show that the odor-induced taste enlancement is elicited by olfactory perception. These results also suggested that there is little functional difference between retronasal and orthonasal olfaction.