Han-k Seo

The influence of olfactory loss on dietary behaviors.

Objectives: To assess dietary behavior and possible changes in food selection in patients with smell loss.

The functional neuroanatomy of odor evoked autobiographical memories cued by odors and words

Behavioral evidence indicates that odor evoked autobiographical memories (OEAMs) are older, more emotional, less thought of and induce stronger time traveling characteristics than autobiographical memories (AMs) evoked by other modalities. The main aim of this study was to explore the neural correlates of AMs evoked by odors as a function of retrieval cue. Participants were screened for specific OEAMs and later presented with the odor cue and its verbal referent in an fMRI paradigm. Because the same OEAM was retrieved across both cue formats (odor and word), potential cue dependent brain activations were investigated. The overall results showed that odor and word cued OEAMs activated regions typically associated with recollection of autobiographical information. Although no odors were presented, a verbal cuing of the OEAMs activated areas associated with olfactory perception (e.g., piriform cortex). However, relative to word cuing, an odor cuing of OEAMs resulted in more activity in MTL regions such as the parahippocampus, and areas involved in visual vividness (e.g., occipital gyrus and precuneus). Furthermore, odor cues activated areas related to emotional processing, such as limbic and tempopolar regions significantly more. In contrast, word cues relative to odor cues recruited a more widespread and bilateral prefrontal activity. Hippocampus activity did not vary as function of the remoteness of the memory, but recollection of OEAMs from the 1(st) vs the 2(nd) decade of life showed specific activation in the right OFC, whereas the 2(nd) reflected a higher activation in the left inferior frontal gyrus.

A salty-congruent odor enhances saltiness: Functional magnetic resonance imaging study

Excessive intake of dietary salt (sodium chloride) may increase the risk of chronic diseases. Accordingly, various strategies to reduce salt intake have been conducted. This study aimed to investigate whether a salty‐congruent odor can enhance saltiness on the basis of psychophysical (Experiment 1) and neuroanatomical levels (Experiment 2). In Experiment 1, after receiving one of six stimulus conditions: three odor conditions (odorless air, congruent, or incongruent odor) by two concentrations (low or high) of either salty or sweet taste solution, participants were asked to rate taste intensity and pleasantness. In Experiment 2, participants received the same stimuli during the functional magnetic resonance imaging scan. In Experiment 1, compared with an incongruent odor and/or odorless air, a congruent odor enhanced not only taste intensity but also either pleasantness of sweetness or unpleasantness of saltiness. In Experiment 2, a salty‐congruent combination of odor and taste produced significantly higher neuronal activations in brain regions associated with odor–taste integration (e.g., insula, frontal operculum, anterior cingulate cortex, and orbitofrontal cortex) than an incongruent combination and/or odorless air with taste solution. In addition, the congruent odor‐induced saltiness enhancement was more pronounced in the low‐concentrated tastant than in the high‐concentrated one. In conclusion, this study demonstrates the congruent odor‐induced saltiness enhancement on the basis of psychophysical and neuroanatomical results. These findings support an alternative strategy to reduce excessive salt intake by adding salty‐congruent aroma to sodium reduced food. However, there are open questions regarding the salty‐congruent odor‐induced taste unpleasantness. Hum Brain Mapp, 2013.

Comparison between Odor Thresholds for Phenyl Ethyl Alcohol and Butanol

UNLABELLED Aim of the study was to compare results of odor threshold test using different numbers of dilution steps, separately for butanol and phenyl ethyl alcohol (PEA). METHODS A total of 116 subjects participated (29 patients with olfactory dysfunction and 87 normosmic subjects). The olfactory threshold for butanol and PEA was examined with 8 (wide step method) and 16 (narrow step method) dilutions. With a delay of about 1 week, all 4 tests were repeated. RESULTS Test time was shortened by approximately 2 min (25%) for patients when using the wide step method. Butanol and PEA thresholds were not significantly different; in addition, a significant correlation was found between thresholds for the 2 odors (r = 0.60, P < 0.001). Threshold test with both odorants as well as with wide or narrow step method provided satisfying reproducibility (test-retest reliability: r = 0.80-0.84, P < 0.001). Patients with olfactory dysfunction could be clearly separated from normosmic subjects using all 4 different tests. DISCUSSION The results indicate that threshold testing with PEA is an alternative to butanol. The wide step method provided similar results as the narrow step method but required less time.

Dissociated Representations of Pleasant and Unpleasant Olfacto-Trigeminal Mixtures: An fMRI Study

How the pleasantness of chemosensory stimuli such as odorants or intranasal trigeminal compounds is processed in the human brain has been the focus of considerable recent interest. Yet, so far, only the unimodal form of this hedonic processing has been explored, and not its bimodal form during crossmodal integration of olfactory and trigeminal stimuli. The main purpose of the present study was to investigate this question. To this end, functional magnetic resonance imaging (fMRI) was used in an experiment comparing brain activation related to a pleasant and a relatively unpleasant olfacto-trigeminal mixture, and to their individual components (CO2 alone, Orange alone, Rose alone). Results revealed first common neural activity patterns in response to both mixtures in a number of regions: notably the superior temporal gyrus and the caudate nucleus. Common activations were also observed in the insula, although the pleasant mixture activated the right insula whereas the unpleasant mixture activated the left insula. However, specific activations were observed in anterior cingulate gyrus and the ventral tegmental area only during the perception of the pleasant mixture. These findings emphasized for the firs time the involvement of the latter structures in processing of pleasantness during crossmodal integration of chemosensory stimuli.

Background sound modulates the performance of odor discrimination task.

Even though we often perceive odors in the presence of various background sounds, surprisingly little is known about the effects of background sound on odor perception. This study aimed to investigate the question whether background sound can modulate performance in an odor discrimination task. In Experiment 1, participants were asked to perform the odor discrimination task while listening to either background noise (e.g., verbal or non-verbal noise) or no additional sound (i.e., silent condition). Participants’ performance in the odor discrimination task was significantly deteriorated in the presence of background noise compared with in the silent condition. Rather, the detrimental effect of verbal noise on the task performance was significantly higher than that of non-verbal noise. In Experiment 2, participants were asked to conduct the odor discrimination task while listening to either background music (Mozart’s sonata for two pianos in D major, K448) or no additional sound (silent condition). Background music relative to silent condition did not significantly alter the task performance. In conclusion, our findings provide new empirical evidence that background sound modulates the performance in an odor discrimination task.

Background music genre can modulate flavor pleasantness and overall impression of food stimuli

This study aimed to determine whether background music genre can alter food perception and acceptance, but also to determine how the effect of background music can vary as a function of type of food (emotional versus non-emotional foods) and source of music performer (single versus multiple performers). The music piece was edited into four genres: classical, jazz, hip-hop, and rock, by either a single or multiple performers. Following consumption of emotional (milk chocolate) or non-emotional food (bell peppers) with the four musical stimuli, participants were asked to rate sensory perception and impression of food stimuli. Participants liked food stimuli significantly more while listening to the jazz stimulus than the hip-hop stimulus. Further, the influence of background music on overall impression was present in the emotional food, but not in the non-emotional food. In addition, flavor pleasantness and overall impression of food stimuli differed between music genres arranged by a single performer, but not between those by multiple performers. In conclusion, our findings demonstrate that music genre can alter flavor pleasantness and overall impression of food stimuli. Furthermore, the influence of music genre on food acceptance varies as a function of the type of served food and the source of music performer.

Congruent Sound Can Modulate Odor Pleasantness

This study aimed to determine 1) whether certain background sounds can be matched with specific odors and 2) whether the background sounds can increase pleasantness for their congruent odors. In Experiment 1, congruent sounds increased odor pleasantness, but not odor intensity, significantly more than incongruent sounds. Experiment 2 demonstrated that certain background sounds can be paired with specific odors. For example, cinnamon, clove, and orange odors were rated significantly more congruent with a Christmas carol compared with the sound of brushing teeth and/or the beach sound. The congruent sounds increased odor pleasantness significantly more than incongruent sounds. Similarly, the congruent sound-induced odor pleasantness was observed in Experiment 3. As participants judged the pair of odor and sound to be more congruent, they rated the odor significantly more pleasant. Congruent sound assisted participants in identifying and in being familiar with the odor, thereby leading to an increase in odor pleasantness. However, the congruent sound-induced odor pleasantness was not obtained in all odors. In conclusion, this study provides new empirical evidence that pleasantness ratings for odors can increase in the presence of their congruent sounds.

A spatiotemporal comparison between olfactory and trigeminal event-related potentials

The present study compared the temporal and spatial aspects of human olfactory and trigeminal processing. A relatively selective trigeminal stimulus, CO2, and a relatively selective olfactory stimulus, H2S, were delivered with an olfactometer to young, healthy volunteers. The analysis was performed in a classical (5-electrode, main ERPs peaks) and modern approach (high topographical resolution, inverse solution, source localization). Results of microstate segmentation highlighted 5 maps that generally described the two processes at cerebral level. The trigeminal response differed from the olfactory response up to 300ms after stimulus onset. In this time range, source analysis pointed out that the olfactory stimulation involved olfactory related areas, while trigeminal stimulation involved noxious/somatosensory specific brain areas. Moreover, from 300ms on our data showed a similarity between the two processes. Statistical parametrical mapping of the differences between conditions suggested greater activation in a specific motor/sniffing network for the CO2 stimulation (probably related to a regulation of the potential noxious stimulus) and a greater activation of the ipsilateral primary olfactory cortex for H2S.

Influence of background noise on the performance in the odor sensitivity task: effects of noise type and extraversion.

Recent research demonstrated that background noise relative to silence impaired subjects’ performance in a cognitively driven odor discrimination test. The current study aimed to investigate whether the background noise can also modulate performance in an odor sensitivity task that is less cognitively loaded. Previous studies have shown that the effect of background noise on task performance can be different in relation to degree of extraversion and/or type of noise. Accordingly, we wanted to examine whether the influence of background noise on the odor sensitivity task can be altered as a function of the type of background noise (i.e., nonverbal vs. verbal noise) and the degree of extraversion (i.e., introvert vs. extrovert group). Subjects were asked to conduct an odor sensitivity task in the presence of either nonverbal noise (e.g., party sound) or verbal noise (e.g., audio book), or silence. Overall, the subjects’ mean performance in the odor sensitivity task was not significantly different across three auditory conditions. However, with regard to the odor sensitivity task, a significant interaction emerged between the type of background noise and the degree of extraversion. Specifically, verbal noise relative to silence significantly impaired or improved the performance of the odor sensitivity task in the introvert or extrovert group, respectively; the differential effect of introversion/extraversion was not observed in the nonverbal noise-induced task performance. In conclusion, our findings provide new empirical evidence that type of background noise and degree of extraversion play an important role in modulating the effect of background noise on subjects’ performance in an odor sensitivity task.