Olfactory event-related potentials in infants.

OBJECTIVES: To evaluate olfactory event-related potentials (OERPs) as an objective measurement of olfactory function in infants. STUDY DESIGN: OERPs to phenylethyl alcohol were measured in 13 infants, between 23 and 41 days of age. The odor was delivered with a computer-controlled olfactometer. Recording electrodes were applied using the 10-20 system. Data from electrodes Fz, Cz, Pz, C3, and C4 were analyzed by MatLab's Letswave toolbox (André Mouraux, Brussels, Belgium) using the canonical time-domain averaging as well as the time-frequency analyzing method. RESULTS: Ten of 13 infants finished the recording session. We observed OERPs in 7 of these 10 infants. Recordings were best in electrodes Fz and Cz. The N1 peak was visible at 328 ms followed by P2 at 505 ms. In addition, the time-frequency analysis had an increase in low frequencies (4-7 Hz) around 550 ms after odor presentation. CONCLUSIONS: We were able to record OERPs in infants. The time-domain averaging as well as the time-frequency analysis was of value for data analysis.

Olfactory bulb volume in patients with idiopathic normal pressure hydrocephalus.

INTRODUCTION: An important pathological feature of idiopathic normal pressure hydrocephalus (iNPH) is a dysfunction of cerebrospinal fluid dynamics. Considering the delicate olfactory structures it appears possible that the olfactory bulb (OB) is compromised by this disease. Reports on the anatomy of the olfactory bulb and smell function in patients with idiopathic normal pressure hydrocephalus are absent in the literature. The main purpose of the present study was to evaluate the olfactory bulb (OB) volume and smell function in iNPH. METHODS: The study comprised 17 patients with iNPH (seven women and ten men, mean age = 66 years); they were compared to a group of 24 healthy people (11 women and 13 men, mean age = 62 years). Comprehensive assessment of olfactory function was conducted with the "Sniffin' Sticks" test kit. In an additional pilot study, in a small subgroup of eight patients, measurements were performed before and approximately 7 months after surgical treatment of the hydrocephalus. RESULTS: The OB volume in patients with iNPH was significantly smaller compared to healthy controls. In our small postoperative patient population (n = 8), there was no significant change of the OB volume. CONCLUSION: In conclusion our results suggest that iNPH significantly affects OB volumes.

Taste laterality studied by means of umami and salt stimuli: an fMRI study.

Aim of the present study was to investigate laterality of the gustatory system in the human brain for the taste qualities elicited by MSG (monosodium glutamate) and NaCl (sodium chloride). A total of 23 subjects participated in a block-design functional magnetic resonance imaging (fMRI) study. Liquid stimuli were presented at supra-threshold concentrations and delivered by means of a computer controlled gustometer. Left and right sides of the mouth were stimulated separately in order to correlate statistical parametrical maps to both the site of the stimulus and the specific taste quality. Following the effects of the site of stimulation through primary and secondary gustatory cortices an effort was made to explore the laterality of the gustatory pathways. Our results showed for both tastants a predominance of ipsilateral connections at the thalamus level. Insula left and right regions were both involved for both tastants. In these regions we found a high proportion of ipsilateral connection again for both the tastants. Considering orbitofrontal/prefrontal cortex, left-sided stimulation with NaCl or MSG produced left-sided activation of the orbito-frontal cortex clearly indicating the presence of an ipsilateral path. Finally, the hypothesis of frontal operculum as primary gustatory cortex and lateral prefrontal cortex as secondary was also supported by the results from dynamic causal modeling.

Investigation of interactions between texture and ortho- and retronasal olfactory stimuli using psychophysical and electrophysiological approaches.

UNLABELLED: Flavor is a result of the complex combination of olfactory, gustatory and trigeminal sensations perceived during oral processing of foods, including thermal, painful, tactile and/or kinesthetic effects. Aim of this study was to better understand interactions between synchronous tactile (texture) and olfactory (odor) sensations, using a psychophysical and an electrophysiological approach. Texture stimuli were aliquots of lean milk and thickened lean milk. A butter aroma was presented either orthonasally or retronasally after oral processing and before swallowing the oral stimulus or in the absence of an oral stimulus. Eighteen subjects (11 women, 7 men, mean age 24 years), naïve to the expected effects, rated both odor and texture intensity of each stimulus. Event-related potentials (ERP) were obtained from five recording positions. For the psychophysical data, the presence of an oral stimulus increased odor intensity, irrespective of odor presentation route. For the electrophysiological data, both early and late chemosensory ERPs were affected by odor conditions, texture conditions, and their respective interaction. IN CONCLUSION: (1) perceptual interactions occurred between food texture and odor, with cross-modal interactions being found for both orthonasal and retronasal odor administration, and (2) these interactions between texture and odor occur at both primary-sensory and cognitive evaluative levels of stimulus processing. The temporal dimension plays then a critical role in the investigation of odor-texture interactions.

Irritancy expectancy alters odor perception: evidence from olfactory event-related potential research.

The aim of the present research was to investigate the influences of cognition on temporal processing of olfactory information in a health-relevant context. We investigated whether expecting an odor to cause adverse health effects alters perception of that odor. An irritation-free odor (Study 1: H(2)S; Study 2: phenyl ethyl alcohol [PEA]) was presented after which participants expected to experience either adverse sensory irritation (caused by intranasal CO(2) presentation) in one condition or no adverse effects in another condition, depending on a previously presented visual cue. Olfactory event-related potentials (OERPs) were measured to assess effects of expectations on the temporal course of olfactory processing. When participants expected irritancy after perceiving the odor of H(2)S, N1 and P3 peak amplitude and N1 latency were increased and shortened, respectively, suggesting more intense and faster processing of the odor as well as effects on salience and anticipation of sensory irritation. When the odor was PEA, only the N1 amplitude was increased. These results, obtained with OERP, provide converging evidence for comparable conclusions regarding the influence of cognition on odor perception reached with functional magnetic resonance imaging. Furthermore, the results suggest that a priori hedonic valence of an odor affects how susceptible the olfactory percept is to modulation via expectations.

Odorant concentration dependence in electroolfactograms recorded from the human olfactory epithelium.

Electroolfactograms (EOGs) are the summated generator potentials of olfactory receptor neurons measured directly from the olfactory epithelium. To validate the sensory origin of the human EOG, we set out to ask whether EOGs measured in humans were odorant concentration dependent. Each of 22 subjects (12 women, mean age = 23.3 yr) was tested with two odorants, either valeric acid and linalool (n = 12) or isovaleric acid and l-carvone (n = 10), each delivered at four concentrations diluted with warm (37 degrees C) and humidified (80%) odorless air. In behavior, increased odorant concentration was associated with increased perceived intensity (all F > 5, all P < 0.001). In EOG, increased odorant concentration was associated with increased area under the EOG curve (all F > 8, all P < 0.001). These findings substantiate EOG as a tool for probing olfactory coding directly at the level of olfactory receptor neurons in humans.

Pupillary responses to intranasal trigeminal and olfactory stimulation.

The aim of the present study was to investigate whether pupillary responses to odorous stimuli reflect their intensity or hedonic tone. A total of 21 healthy subjects participated in the study. Using a computer-controlled olfactometer, subjects received intranasal stimuli including odors of rose (PEA; 2 concentrations), lemon and rotten eggs, plus the trigeminal irritant CO2 (also at two concentrations). Changes in the pupil diameter were obtained ipsilaterally to the side of stimulus presentation. Both trigeminal and olfactory stimulation produced an increase in pupillary diameter. Latencies for pupillary reaction were fastest for the higher concentration of CO2 and slowest after the presentation of PEA at the low concentration. Response amplitudes were largest in response to stimulation with CO2 at the high concentration, while they were smallest in response to odorous stimulation with PEA. Response latencies decreased with increasing stimulus intensity. No such correlation was found for hedonic ratings and pupillary reactions. Thus, the change in the pupillary diameter indicates differences between stimulus modalities and stimulus strength, but not pleasantness or unpleasantness of the odors.

Evaluation of trigeminal sensitivity to ammonia in asthmatics and healthy human volunteers.

Asthmatics often report the triggering or exacerbation of respiratory symptoms following exposure to airborne irritants, which in some cases may result from stimulation of irritant receptors in the upper airways inducing reflexive bronchoconstriction. Ammonia (NH3) is a common constituent of commercially available household products, and in high concentration has the potential to elicit sensory irritation in the eyes and upper respiratory tract of humans. The goal of the present study was to evaluate the irritation potential of ammonia in asthmatics and healthy volunteers and to determine whether differences in nasal or ocular irritant sensitivity to ammonia between these two groups could account for the exacerbation of symptoms reported by asthmatics following exposure to an irritant. Twenty-five healthy and 15 mild/moderate persistent asthmatic volunteers, with reported sensitivity to household cleaning products, were evaluated for their sensitivity to the ocular and nasal irritancy of NH3. Lung function was evaluated at baseline and multiple time points following exposure. Irritation thresholds did not differ between asthmatics and healthy controls, nor did ratings of odor intensity, annoyance, and irritancy following exposure to NH3 concentrations at and above the irritant threshold for longer periods of time (30 s). Importantly, no changes in lung function occurred following exposure to NH3 for any individuals in either group. Thus, despite heightened symptom reports to environmental irritants among asthmatics, the ocular and nasal trigeminal system of mild to moderate asthmatics does not appear to be more sensitive or more reactive than that of nonasthmatics, nor does short-duration exposure to ammonia at irritant levels induce changes in lung function. At least in brief exposures, the basis for some asthmatics to experience adverse responses to volatile compounds in everyday life may arise from factors other than trigeminally mediated reflexes.

Interactions between olfaction and the trigeminal system: what can be learned from olfactory loss.

The olfactory and the trigeminal systems have a close relationship. Most odorants also stimulate the trigeminal nerve. Further, subjects with no sense of smell exhibit a decreased trigeminal sensitivity with unclear underlying mechanisms. Previous studies indicated that single stages of trigeminal processing may differently be affected by olfactory loss. A better knowledge of adaptive and compensatory changes in the trigeminal system of subjects with acquired anosmia (AA) will improve the understanding of interactive processes between the 2 sensory systems. Thus, we aimed to assess trigeminal function on different levels of processing in subjects with AA. Subjects with AA showed larger electrophysiological responses to irritants obtained from the mucosa than healthy controls. On central levels, however, they exhibited smaller event-related potentials and psychophysical measures to irritants. Over 9 months, they exhibited an increase in trigeminal sensitivity. Subjects with recovering olfactory function showed an even more increased peripheral responsiveness to irritants. These data suggest dynamic mechanisms of mixed sensory adaptation/compensation in the interaction between the olfactory and trigeminal systems, where trigeminal activation is increased on mucosal levels in subjects with AA and amplified on central levels in subjects with a functioning olfactory system.