Biomedical subjects

Thomas Hummel

Publications and source records attributed to Thomas Hummel.

At least 37 records · Page 2Linked to original sources

PubMed2006

Dendritic patterning by Dscam and synaptic partner matching in the Drosophila antennal lobe.

In the olfactory system of Drosophila melanogaster, axons of olfactory receptor neurons (ORNs) and dendrites of second-order projection neurons typically target 1 of approximately 50 glomeruli. Dscam, an immunoglobulin superfamily protein, acts in ORNs to regulate axon targeting. Here we show that Dscam acts in projection neurons and local interneurons to control the elaboration of dendritic fields. The removal of Dscam selectively from projection neurons or local interneurons led to clumped dendrites and marked reduction in their dendritic field size. Overexpression of Dscam in projection neurons caused dendrites to be more diffuse during development and shifted their relative position in adulthood. Notably, the positional shift of projection neuron dendrites caused a corresponding shift of its partner ORN axons, thus maintaining the connection specificity. This observation provides evidence for a pre- and postsynaptic matching mechanism independent of precise glomerular positioning.

Animals↗

PubMed2006

Wiring specificity in the olfactory system.

The fruitfly brain learns about the olfactory world by reading the activity of about 50 distinct channels of incoming information. The receptor neurons that compose each channel have their own distinctive odour response profile governed by a specific receptor molecule. These receptor neurons form highly specific connections in the first olfactory relay of the fly brain, each synapsing with specific second order partner neurons. We use this system to discuss the logic of wiring specificity in the brain and to review the cellular and molecular mechanisms that allow such precise wiring to develop.

Animals↗

PubMed2006

Electro-olfactograms are present when odorous stimuli have not been perceived.

After chemical stimulation of the human olfactory epithelium it is possible to record a negative response (electro-olfactogram, EOG) which is interpreted as the summated generator potential of olfactory neurons. The aim of the present investigation was to test whether the EOG is present when olfactory stimuli have not been perceived. Stimulation was performed with vanillin and eugenol at supraliminal and subliminal levels. Twelve healthy volunteers participated in the experiments. Stimuli were applied at an interstimulus interval of approximately 60s. Although recordings were successful in 4 of the 12 subjects, for both stimulants EOG could be obtained even when the stimuli had not been perceived by the subjects. EOG recordings in response to supra- and subliminal stimuli exhibited no major differences, except for the onset of the EOG in response to subliminal eugenol-stimuli which were prolonged compared to supraliminal stimulation. All in all, the present data provide a physiological basis for the subliminal influence of odorous stimuli on human behavior.

Adult↗

PubMed2006

The influence of stimulus duration on odor perception.

Although different parameters are known to alter the shape of olfactory event related potentials (ERP), ERP parameters are generally thought to be independent from stimulus duration. Evidence from recent studies investigating trigeminal ERP indicates that this may not be true. Aim of the present study was to investigate the relationship of stimulus duration and ERP. A total of 20 young healthy subjects participated. Subjects were investigated on 5 occasions on 5 different days. ERP were recorded to olfactory stimuli of two different concentrations and 3 different durations (100 ms, 200 ms, 300 ms). In two sessions olfactory ERP to PEA were recorded, in another two sessions H2S was applied. During the same sessions, intensity ratings were recorded. In the fifth session, subjects were asked to rate the duration of H2S stimuli and PEA stimuli. Whereas at weak stimulus concentrations no effect of stimulus duration could be observed, there was a clear effect of "duration" in ERP amplitudes following stimuli with higher concentrations: the longer the stimulus duration the larger the ERP amplitudes. No effect was found on ERP latencies. With regard to intensity ratings, strong stimuli and longer lasting stimuli lead to higher ratings. Similarly, ratings of stimulus duration were dependent from stimulus concentration and stimulus duration. Results of the present study showed that similar to trigeminal ERP, information about stimulus duration is encoded in olfactory ERP, mainly in amplitudes.

Adult↗

PubMed2006

A putative social chemosignal elicits faster cortical responses than perceptually similar odorants.

Social chemosignals, so-called pheromones, have recently attracted much attention in that effects on women's psychophysiology and cortical processing have been reported. We here tested the hypothesis that the human brain would process a putative social chemosignal, the endogenous steroid androstadienone, faster than other odorants with perceptually matched intensity and hedonic characteristics. Chemosensory event-related potentials (ERP) were recorded in healthy women. ERP analyses indicate that androstadienone was processed significantly faster than the control odorants. Androstadienone elicited shorter latencies for all recorded ERP components but most so for the late positivity. This finding indicates that androstadienone is processed differently than other related odorants, suggesting the possibility of a specific neuronal subsystem to the main olfactory pathway akin to the one previously reported in Old-world monkeys and emotional visual stimuli in humans.

Adult↗

PubMed2006

Olfactory function assessed with orthonasal and retronasal testing, olfactory bulb volume, and chemosensory event-related potentials.

OBJECTIVE: To investigate whether differences in olfactory function between healthy individuals and patients with olfactory loss could be detected by various diagnostic tests. DESIGN: Psychophysical testing of orthonasal and retronasal olfactory functions, magnetic resonance imaging of olfactory bulb (OB) volume, and chemosensory event-related potential (ERP) measurement performed between January 1, 2005, and October 31, 2005. SETTING: Academic tertiary referral medical center. PATIENTS: Eleven healthy individuals with normal olfactory function (NL) and 11 patients with nasal polyposis (NP), 11 with posttraumatic olfactory loss (PT), and 11 with postinfectious olfactory loss (PI) were included in this study. MAIN OUTCOME MEASURES: Orthonasal and retronasal olfactory test results, magnetic resonance imaging-based OB volume, and ERPs to both olfactory and intranasal trigeminal stimulation. RESULTS: Orthonasal and retronasal testing revealed that NL individuals had higher scores than patients with NP, PT, or PI. Retronasal scores were higher in NP patients compared with PT and PI patients. The OB volumes were higher in NL individuals compared with NP, PT, and PI patients. The OB volumes in PT patients were significantly lower than those from NP and PI patients. Olfactory ERPs were different between NL individuals and NP, PT, and PI patients, and trigeminal ERPs were significantly different when comparing NL individuals with NP patients. For the entire cohort, a significant correlation was found between orthonasal testing and OB volume, between retronasal testing and OB volume, and between both orthonasal and retronasal testing and olfactory ERP amplitudes. Olfactory ERPs were recorded in the 11 NL individuals and in 3 NP, 3 PT, and 4 PI patients, defined as responders. Orthonasal and retronasal test scores, OB volume, and olfactory ERPs were significantly larger in responders compared with nonresponders. CONCLUSIONS: Significant differences in various tests that evaluate olfactory function were detectable in a cohort of NL individuals and NP, PT, and PI patients. This finding suggests that these diagnostic tools provide information in terms of the clinical assessment of olfactory function. Future studies will investigate their combined use in terms of the prognosis of olfactory function in patients with olfactory loss.

Action Potentials↗

PubMed2006

Recovery of olfactory function following closed head injury or infections of the upper respiratory tract.

OBJECTIVE: To investigate the outcome of olfactory function in patients with olfactory loss following infections of the upper respiratory tract (post-URTI) or head trauma. DESIGN: Retrospective patient-based study. SETTING: Smell and Taste Outpatient Clinic at a university hospital. PATIENTS: A total of 361 patients (228 women, 133 men) were included. MAIN OUTCOME MEASURES: Olfactory function was assessed using the "Sniffin' Sticks" test battery, which result in a threshold, discrimination, and identification score. The mean interval between first and last visit was 14 months. RESULTS: In comparing the overall threshold, discrimination, and identification scores between the last and first visit, olfactory function improved in 26% of the patients whereas it decreased in 6%. The cause of olfactory impairment had a significant effect on the recovery rate of olfactory function. Within the post-URTI group (n = 262), 32% of the patients improved, but in the posttraumatic group (n = 99) only 10% improved. In patients with post-URTI olfactory loss, a negative correlation was found between age and recovery of olfactory function. In general, the factor "sex" had no significant effect on recovery of smell function. CONCLUSIONS: To our knowledge, the series of patients presented herein is the largest in the literature to date in which standardized testing methods were used to assess the progression of impaired olfaction. It showed that the rate of improvement of olfactory function was significantly higher in patients with post-URTI dysosmia compared with patients with posttraumatic dysosmia. During an observation period of approximately 1 year, more than 30% of patients with post-URTI olfactory loss experienced improvement, whereas only 10% of patients with posttraumatic olfactory loss experienced improvement. Furthermore, age plays a significant role in the recovery of olfactory function.

Adolescent↗

PubMed2006

Different swelling mechanisms in nasal septum (Kiesselbach area) and inferior turbinate responses to histamine: an optical rhinometric study.

OBJECTIVE: To determine whether the inferior turbinate, which contains swelling bodies, and the nasal septum (Kiesselbach area), characterized by a dense arterial mesh, exhibit different swelling mechanisms in allergic nasal reactions. DESIGN: Two optical rhinometers were used to examine 11 patients in the clinic. Optical rhinometry is based on the transillumination of the nasal septum and inferior turbinate or the whole nose with monochromatic light. The instrument's wavelength can be adjusted to the absorption characteristics of reduced hemoglobin, oxygen-saturated hemoglobin, and water. SETTING: Outpatient university otolaryngology clinic. PATIENTS: Eleven young, healthy, nonsmoking, nonpregnant subjects (6 men and 5 women), mean age, 32.4 years (age range, 27-37 years), with no history of exposure to toxic substances, allergies, or other significant diseases. INTERVENTIONS: Optic rhinometry evaluation during the course of nasal histamine administration. MAIN OUTCOME MEASURES: Light extinction at various wavelengths. RESULTS: Following administration of histamine, in the nasal septum, the wavelength of 950 nm (edema) showed the strongest increase of light extinction; in the inferior turbinate, it was the wavelength of 786 nm (oxygenated hemoglobin). In the whole nose, the wavelength of 880 nm (edema plus hemoglobin) exhibited the largest increase of extinction. CONCLUSIONS: Swelling of the nasal septum (Kiesselbach area) in nasal allergic reactions is caused mainly by edema, whereas swelling of the inferior turbinate is due mainly to an increase in volume of blood that is highly saturated with oxygen. Swelling of the whole nose is characterized by the combination of both, edema and increase in blood volume.

Adult↗

PubMed2006

Extrapyramidal symptoms in Wilson's disease are associated with olfactory dysfunction.

Wilson's disease is a rare autosomal recessive disorder characterized by the accumulation of copper, mainly in the liver and the brain. As copper accumulation in the brain leads to disturbances in basal ganglia function, neurological-type patients typically present with hypo- and hyperkinetic extrapyramidal symptoms, with Parkinsonism being very common. Although there are numerous reports on olfactory deficits in primary neurodegenerative disorders, olfactory function has not been investigated in metabolic disorders presenting with extrapyramidal features. Twenty-four patients with Wilson's disease participated in the investigation. All patients were treated pharmacologically. They comprised patients with liver disease alone (including mild enzyme elevation in asymptomatic individuals; n = 11) and/or neurological symptoms (n = 13) at the time of testing. Twenty-one patients underwent both [18F]fluoro-2-deoxy-D-glucose positron emission tomography ([18F]FDG-PET) and magnetic resonance imaging (MRI). The severity of extrapyramidal symptoms was judged using a clinical score system ranging from 0 (no symptoms) to 3 (severe symptoms). In all patients, psychophysical testing was performed using the Sniffin' Sticks, which involved tests for odor threshold, discrimination, and identification. Results from the present study revealed that Wilson's disease patients with neurological symptoms show a significant olfactory dysfunction compared to hepatic-type patients. Individuals who are more severely neurologically affected also present with a more pronounced olfactory deficit. Of interest, there was no significant effect of long-term treatment with penicillamine on olfactory function. Olfactory function did not correlate significantly with the presence of MRI visible lesions in the basal ganglia or with any regional glucose metabolism as measured by [18]F-FDG-PET. In conclusion, these findings indicate that the underlying pathological alterations with degeneration in the basal ganglia and neuronal loss in association with a marked increase of the copper content in this brain region play a role in the olfactory deficit.

Adult↗

PubMed2006

On the trigeminal percept of androstenone and its implications on the rate of specific anosmia.

Specific anosmia is a term that describes an inability to perceive a particular odorant in the context of an otherwise normal olfactory acuity. The most common example, for the odor of androstenone, has been ascribed a prevalence ranging from 2 to 45%. In two experiments we sought to determine whether this wide range could be explained by the difference in steroid concentrations used, and by the degree to which the trigeminal system contributes to perception of androstenone. Experiment 1 demonstrated that high concentrations of androstenone stimulated the trigeminal system, as indicated by electrophysiological recordings. Experiment 2 demonstrated that conscious detection of androstenone is possible based solely on the trigeminal system. Interestingly, detection seems to interact with olfactory acuity in that subjects with a low olfactory sensitivity to androstenone were better able to detect its trigeminal component. The agreement between conscious experience and behavioral discrimination was not well calibrated, in that subjects demonstrated a clear overconfidence in their abilities. Altogether, the current study suggests that androstenone is an odorant that produces a concentration-dependent degree of trigeminal stimulation. This trigeminal component explains the diversity of the reported prevalence of specific anosmia for androstenone and might have implications on future use of specific anosmia as a tool to understand odor processing.

Adult↗

PubMed2006

Vomeronasal versus olfactory epithelium: is there a cellular basis for human vomeronasal perception?

The vomeronasal organ (VNO) constitutes an accessory olfactory organ that receives chemical stimuli, pheromones, which elicit behavioral, reproductive, or neuroendocrine responses among individuals of the same species. In many macrosmatic animals, the morphological substrate constitutes a separate organ system consisting of a vomeronasal duct (ductus vomeronasalis, VND), equipped with chemosensory cells, and a vomeronasal nerve (nervus vomeronasalis, VNN) conducting information into the accessory olfactory bulb (AOB) in the central nervous system (CNS). Recent data require that the long-accepted dual functionality of a main olfactory system and the VNO be reexamined, since all species without a VNO are nevertheless sexually active, and species possessing a VNO also can sense other than "vomeronasal" stimuli via the vomeronasal epithelium (VNE). The human case constitutes a borderline situation, as its embryonic VNO anlage exerts a developmental track common to most macrosmatics, but later typical structures such as the VNN, AOB, and probably most of the chemoreceptor cells within the still existent VND are lost. This review also presents recent information on the VND including immunohistochemical expression of neuronal markers, intermediate filaments, lectins, integrins, caveolin, CD44, and aquaporins. Further, we will address the issue of human pheromone candidates.

Animals↗

PubMed2006

Effects of long-term exposure to volatile irritants on sensory thresholds, negative mucosal potentials, and event-related potentials.

This study examined whether repetitive exposure to an irritant stimulant leads to desensitization and whether such modulation influences the psychological or the physiological response to that chemical. Subjects were exposed to acetic acid vapor in their home environment. Before, during, and after 3 weeks of daily exposure, the authors obtained electrophysiological recordings at peripheral and central levels in combination with psychophysical responses to acetic acid and acetone. Responses to acetic acid decreased during and following exposure. This did not generalize to the control irritant. Thresholds measured 1 year following exposure returned to baseline levels. In summary, repetitive exposure to an irritant vapor results in a specific desensitization to irritancy from that chemical, which appears to originate at a peripheral level.

Acetic Acid↗

PubMed2006

The human mu-opioid receptor gene polymorphism 118A > G decreases cortical activation in response to specific nociceptive stimulation.

The authors sought to investigate the role of a common single nucleotide polymorphism in the mu-opioid receptor gene (OPRM1) 118A > G for nociceptive sensory processing using event-related potentials (ERPs). Specific nociceptive (carbon dioxide [CO-sub-2]: 40% volume-to-volume [vol/vol] and 60% vol/vol) and nonnociceptive (hydrogen sulfide, 2 parts per million [ppm] and 4 ppm) stimuli were applied to the nasal mucosa of 45 volunteers. ERPs were recorded from a central lead. In this random sample, we found 37 noncarriers, 7 heterozygous carriers, and 1 homozygous carrier of the variant OPRM1 118G allele (allelic frequency, 10%). Amplitudes of nociceptive ERP in carriers of this allele were, on average, half as high as those of noncarriers. In discriminant analysis, ERP amplitude N1 response to the weaker nociceptive stimuli was the only ERP parameter that discriminated statistically significantly between carriers and noncarriers of the variant 118G allele. On the basis of N1-CO-sub-2 (40% vol/vol), the authors correctly backclassified 68.6% of the cases as carriers or noncarriers of the allele. The OPRM1 118A > G polymorphism specifically modulates nociceptive but not nonnociceptive cortical activation.

Adult↗

PubMed2006

Olfactory function and olfactory bulb volume in patients with postinfectious olfactory loss.

OBJECTIVE: The study aimed to investigate whether the degree of postinfectious olfactory loss is reflected in volume of the olfactory bulb (OB). STUDY DESIGN: Retrospective study of 26 patients with postinfectious olfactory loss. MATERIALS AND METHODS: Olfactory function was assessed with the "Sniffin' Sticks" test kit, and the magnetic resonance imaging study focused on OB volume and the olfactory sulcus. RESULTS: The study revealed that 1) OB volume varies with regard to olfactory function, 2) OB volume decreases with duration of olfactory loss, and 3) patients with parosmia had smaller OB volumes than patients who did not report such smell distortions, although their overall olfactory function was not significantly different from each other. CONCLUSION: The study emphasizes that OB volume is a gauge of olfactory function.

Adult↗

PubMed2006

Retronasal and orthonasal olfactory function in relation to olfactory bulb volume in patients with posttraumatic loss of smell.

OBJECTIVE: The aims of this study were to evaluate olfactory function with orthonasal and retronasal testing in patients with posttraumatic olfactory loss and to investigate the relation between residual olfactory function and olfactory bulb (OB) volume. METHOD: A retrospective study of 25 patients with posttraumatic olfactory loss was performed. Orthonasal olfactory function was assessed with the Sniffin' Sticks test kit; retronasal olfactory function was assessed with intraorally applied odors. Magnetic resonance imaging was used to determine OB volume and cortical damage in the frontal and temporal areas. RESULTS: The main outcomes of the present study were the demonstration of a correlation between olfactory function and OB volume, which was more pronounced for retronasal than for orthonasal olfactory function; retronasal olfactory function was most affected in the patients with the most extensive cerebral damage and was least compromised in patients without such damage; OB volumes were smaller in patients with parosmia compared with those without; and the presence of parosmia was clearly associated with the presence of cerebral damage. CONCLUSION: The data confirm that OB volume is an indicator of olfactory function but, interestingly, in this study, it is largely determined by retronasal olfactory sensitivity. In addition, these results emphasize the role of higher cortical centers in olfactory function, and especially in parosmia, which may, at least in some cases, be related to lesions in the fronto-orbital and anterior temporal cortices. It would be of interest to investigate OB volume further in relation to the prognosis of the disorder.

Adult↗

PubMed2006

Contact endoscopic comparison of morphology of human fungiform papillae of healthy subjects and patients with transected chorda tympani nerve.

BACKGROUND: The chorda tympani nerve (CTN) carries gustatory fibers from taste buds of fungiform papillae (fPap) of the anterior portion of the tongue. Accordingly, middle ear surgery with transection of the CTN may result in gustatory impairment. With use of contact endoscopy, the present study aimed to compare number and shape of fPap and subepithelial vessel formation in patients after CTN transection with that of healthy controls. MATERIAL AND METHODS: The number of fPap per square centimeter was obtained in addition to measures of gustatory sensitivity using electrogustometry and intensity ratings of natural taste stimuli. Data from 32 healthy subjects (mean age 40 yr; 16 female, 16 male) were compared with those from 14 patients whose CTN had been cut and partly resected during middle ear surgery because of cholesteatoma (mean age 38 yr; 7 female, 7 male). Middle ear surgery was performed by two of the authors. RESULTS: In healthy subjects, a higher fPap density was found on the tongue's tip compared with its edge; younger subjects had higher densities than older subjects. No sex-related differences were observed. Patients with transected CTN exhibited a significant decrease of taste function as measured with both natural and electric stimuli. In patients, we found significantly fewer and flatter fPap on the side of the tongue where surgery had been performed in comparison with the contralateral side. In addition, fPap density at the ipsilateral side was significantly lower compared with fPap density on the respective side in healthy controls. CONCLUSION: As established through contact endoscopy, the number of fPap decreases in relation to deafferentation and also in relation to the subjects' age, both of which are accompanied by a decreased gustatory sensitivity.

Adolescent↗

PubMed2006

Loss of trigeminal sensitivity reduces olfactory function.

The trigeminal and olfactory nerves share overlapping innervation areas in the nasal cavity and seem to work in an interactive way. Loss of olfactory function leads to a decreased trigeminal sensitivity, as shown in anosmic subjects. To report the impact of disturbed trigeminal sensitivity on the olfactory function, we present a patient with unilateral loss of trigeminal function resulting from a meningeoma. Thresholds to a selective olfactory stimulus were elevated by a factor of 64 on the affected side. Recordings of event-related potentials in response to olfactory stimuli showed a significantly reduced response on the affected side. This report indicates that loss of trigeminal function may affect the sense of smell.

Female↗

PubMed2006

Clinical significance of results from olfactory testing.

BACKGROUND: Although widely used in healthy subjects and patients with olfactory loss, the significance of changes of scores from validated olfactory tests is unknown. AIM AND METHODS: The aim of the present study was to relate the self-assigned changes of olfactory function in terms of "better," "unchanged," and "worse" in patients with smell disorders with the results from olfactory testing by means of a validated test set. Olfactory function of 83 anosmic or hyposmic patients (40 women, 43 men; age 12-84 yr) was tested on two occasions (mean interval 136 days, minimum 7 days, maximum 6.7 yr). Olfactory function was assessed using a validated technique ("Sniffin' Sticks"). This test consists of three subtests, one for odor threshold (T), odor discrimination (D), and odor identification (I), with possible results ranging up to 16 points each. From the sum of the results from the three subtests a composite "TDI" score was obtained. RESULTS: Forty-four patients indicated an improvement of olfactory function, whereas 39 patients reported no change. No subject reported deterioration of olfactory sensitivity. Subjects assigned to group BETTER had higher TDI scores in the second olfactory tests than subjects assigned to the group UNCHANGED, both in absolute terms and as compared with the first olfactory test (effect "test occasion" by "self-assessed improvement," P < .001). There was no significant difference between groups with respect to age and sex (P = .99 and .84, respectively). Logistic regression showed that more than 60% of the subjects reported an improvement of olfactory sensitivity when the TDI score increased by 5.5 points. CONCLUSION: We show that there is a statistically significant relation between measured and perceived improvement of olfactory function in patients who first presented with the diagnosis of anosmia or hyposmia. The results indicate that improved olfactory function in patients with olfactory deficiency is perceived as such in everyday life and is quantitatively related to an improvement in the composite TDI score of the "Sniffin' Sticks" olfactory test battery. This is the basis for the application of a specific therapy for olfactory loss because of a possible gain in quality of life for the patients.

Adolescent↗