White matter changes in the perforant path area in patients with amyotrophic lateral sclerosis.

OBJECTIVE: The aim of this study was to test the hypothesis that white matter degeneration of the perforant path - as part of the Papez circuit - is a key feature of amyotrophic lateral sclerosis (ALS), even in the absence of frontotemporal dementia (FTD) or deposition of pTDP-43 inclusions in hippocampal granule cells. METHODS: We used diffusion Magnetic Resonance Imaging (dMRI), polarized light imaging (PLI) and immunohistochemical analysis of post mortem hippocampus specimens from controls (n = 5) and ALS patients (n = 14) to study white matter degeneration in the perforant path. RESULTS: diffusion Magnetic Resonance Imaging demonstrated a decrease in fractional anisotropy (P = 0.01) and an increase in mean diffusivity (P = 0.01) in the perforant path in ALS compared to controls. PLI-myelin density was lower in ALS (P = 0.05) and correlated with fractional anisotropy (r = 0.52, P = 0.03). These results were confirmed by immunohistochemistry; both myelin (proteolipid protein, P = 0.03) and neurofilaments (SMI-312, P = 0.02) were lower in ALS. Two out of the fourteen ALS cases showed pTDP-43 pathology in the dentate gyrus, but with comparable myelination levels in the perforant path to other ALS cases. CONCLUSION: We conclude that degeneration of the perforant path occurs in ALS patients and that this may occur before, or independent of, pTDP-43 aggregation in the dentate gyrus of the hippocampus. Future research should focus on correlating the degree of cognitive decline to the amount of white matter atrophy in the perforant path.

Endovascular stroke treatment does not preclude high thrombolysis rates.

BACKGROUND AND PURPOSE: In 1995 intravenous recombinant tissue plasminogen activator (IVRTPA) was the first reperfusion therapy to be approved in patients with acute ischaemic stroke (AIS). The significance and impact of IVRTPA in times of modern endovascular stroke treatment (EST) were analysed in a German academic stroke centre. METHODS: A retrospective observational cohort analysis of 1034 patients with suspected AIS presenting at the emergency department in 2014 was performed. Patients were evaluated for baseline characteristics, reperfusion procedures, IVRTPA eligibility, clinical outcome, symptomatic intracranial haemorrhage (sICH) and mortality. Data acquisition was part of an investigator-initiated, prospective and blinded end-point registry. RESULTS: In 718 (69%) patients the diagnosis of symptomatic AIS was confirmed. 419 (58%) patients presented within 4.5 h of symptom onset and of those 260 (62%) received reperfusion therapy (IVRTPA alone, n = 183; combination or bridging therapy, n = 60; EST alone, n = 17). Subtracting cases with absolute contraindications for IVRTPA resulted in an effective thrombolysis rate of 82%. sICH occurred in two patients treated with IVRTPA alone (1.1%). The median door-to-needle interval was 30 min. Fifty (17%) non-EST eligible AIS patients presenting within 4.5 h without absolute contraindications did not receive IVRTPA mainly due to mild or regressive symptoms. Most of these untreated IVRTPA eligible patients (82%) were discharged with a good clinical outcome (modified Rankin Scale ≤ 2). CONCLUSIONS: Intravenous recombinant tissue plasminogen activator remains the most frequently applied reperfusion therapy in AIS patients presenting within 4.5 h of onset in a tertiary stroke centre. An effective thrombolysis rate of over 80% can be achieved without increased rates of sICH.

Instrument Calibration of the Interface Region Imaging Spectrograph (IRIS) Mission.

The Interface Region Imaging Spectrograph (IRIS) is a NASA small explorer mission that provides high-resolution spectra and images of the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The IRIS data are archived in calibrated form and made available to the public within seven days of observing. The calibrations applied to the data include dark correction, scattered light and background correction, flat fielding, geometric distortion correction, and wavelength calibration. In addition, the IRIS team has calibrated the IRIS absolute throughput as a function of wavelength and has been tracking throughput changes over the course of the mission. As a resource for the IRIS data user, this article describes the details of these calibrations as they have evolved over the first few years of the mission. References to online documentation provide access to additional information and future updates.

Implant-specific follow-up imaging of treated intracranial aneurysms: TOF-MRA vs. metal artifact reduced intravenous flat panel computed tomography angiography (FPCTA).

AIM: To compare the diagnostic quality of time-of-flight magnetic resonance angiography (TOF-MRA) and metal-artefact-reduction (MAR) flat-panel-detector computed tomography angiography (FPCTA) and to determine the imaging technique best suited for evaluation endovascular and surgically treated aneurysms. METHODS: The image quality of TOF-MRA and MAR-FPCTA of 44 intracranial implants (coiling: n=20; clipping: n=15; coiling + stenting: n=9) in a patient cohort of 25 was evaluated by two independent readers. Images obtained using MAR-FPCTA (20 second scan time, 496 projections, intravenous contrast medium administration; Artis Zee, Siemens Healthcare, Forchheim) were compared with TOF-MRA-images (1.5 or 3 T). Nominal data were analysed using McNemar's chi-square test and ordinal variables using the Wilcoxon rank test. RESULTS: Compared to TOF-MRA, MAR-FPCTA was significantly better suited to detect aneurysm remnants and to evaluate parent vessels after clipping (p<0.01). For coil packages >160 mm3, TOF-MRA provided significantly better assessment than MAR-FPCTA (p<0.01). For small coil packages (<160 mm3), no significant difference between TOF-MRA and MAR-FPCTA (p=0.232) was observed. For different clip sizes (cut-off 492 mm3) likewise no significant differences were found. The interobserver comparison showed high interrater agreement. CONCLUSION: MAR-FPCTA is significantly better suited for follow-up examinations of clipped aneurysms, whereas for larger coil packages TOF-MRA is preferable. Smaller coil packages can be analysed using MAR-FPCTA or TOF-MRA.

Butyrate restores HFD-induced adaptations in brain function and metabolism in mid-adult obese mice.

OBJECTIVE: Midlife obesity affects cognition and increases risk of developing dementia. Recent data suggest that intake of the short chain fatty acid butyrate could improve memory function, and may protect against diet-induced obesity by reducing body weight and adiposity. SUBJECTS: We examined the impact of a high-fat diet (HFD) followed by intervention with 5% (w/w) dietary butyrate, on metabolism, microbiota, brain function and structure in the low-density-lipoprotein receptor knockout (LDLr-/-) mouse model in mid and late life. RESULTS: In mid-adult mice, 15 weeks of HFD-induced adiposity, liver fibrosis and neuroinflammation, increased systolic blood pressure and decreased cerebral blood flow, functional connectivity assessed with neuroimaging. The subsequent 2 months butyrate intervention restored these detrimental effects to chow-fed control levels. Both HFD and butyrate intervention decreased variance in fecal microbiota composition. In late-adult mice, HFD showed similar detrimental effects and decreased cerebral white and gray matter integrity, whereas butyrate intervention attenuated only metabolic parameters. CONCLUSION: HFD induces detrimental effects in mid- and late-adult mice, which can be attenuated by butyrate intervention. These findings are consistent with reported associations between midlife obesity and cognitive impairment and dementia in humans. We suggest that butyrate may have potential in prevention and treatment of midlife obesity.

Neurothrombectomy in acute ischaemic stroke: a prospective single-centre study and comparison with randomized controlled trials.

BACKGROUND AND PURPOSE: In the last few months five multicentre, randomized controlled trials (RCTs) unequivocally showed the superiority of mechanical thrombectomy in large vessel occlusion acute ischaemic stroke compared to systemic thrombolysis. Despite varying inclusion criteria and time intervals from onset to revascularization overall increases of good functional outcome between 55% and 81% were reported. However, only a minority of screened patients (approximately 1%) were eligible for intra-arterial (IA) therapy. METHODS: An investigator-initiated, single-centre, prospective and blinded end-point analysis was performed of 3123 consecutive patients with acute ischaemic stroke presenting between February 2010 and December 2014. RESULTS: One hundred and fifty-four patients [4.9%, age (years) mean (SD), median (interquartile range) 71.2 (±14), 74.7 (65.9-81.4)] met the inclusion criteria of sparse early ischaemic signs on initial standard cranial computed tomography (CT) (ASPECT score ≥7), large vessel occlusion in the anterior circulation on CT angiography and start of treatment within 6 h of onset of symptoms. After consensual interdisciplinary treatment decisions 130 patients (4.2%) received IA treatment - in the majority stent-assisted thrombectomy in combination with intravenous (IV) recombinant tissue plasminogen activator - and 24 patients (0.7%) standard IV thrombolysis. On 3 months' follow-up an overall significant improvement of disability (P = 0.05) as measured by the modified Rankin Scale was shown in favour of the IA treatment group. Good functional outcome was achieved in about twice as many patients (IA vs. IV, 41.2% vs. 21.2%; P = 0.078). CONCLUSION: By choosing pragmatic inclusion criteria state-of-the-art IA therapy of a specialized tertiary stroke centre can be safely applied under real-world conditions to a higher percentage of patients with similar success to the recently published RCTs.

Transient cortical blindness after diagnostic cerebral angiography - A single center report.

Background: Transient cortical blindness (TCB) has been reported as a complication after diagnostic cerebral angiography in 0.3-1% of cases. Our aim was to observe the frequency of TCB after diagnostic cerebral angiography over a period of 11 years using only hypo-osmolar, nonionic contrast agents and following a protocol to reduce both the total volume of injected contrast agent and the number of angiography series obtained. Methods: We retrospectively included all 2431 patients who received diagnostic cerebral angiographies at our institution. Primary outcome measure was the occurrence of TCB after diagnostic cerebral angiography, hypothesizing that the occurrence of TBC depends on the volume of contrast agent and angiography of the vertebrobasilary arteries. Results: Over the analyzed time period of 11 years, we did not observe a single case of TCB following diagnostic cerebral angiography. The median contrast volume used was 100 ml (IQR, 100-200), ranging from 15 ml to 500 ml. In our cohort, 61.5% of patients received a selective catheterization of the vertebrobasilary territory. In 99.8% of angiographies iopamidol was used a contrast agent. Conclusion: Our results indicate that following to certain aspects of the angiography protocol (using the hypoosmolar, non-ionic contrast agent iopamidol and reducing the number of catheterized vessels and angiography series to a diagnostic minimum) the frequency of transient cortical blindness as a complication of diagnostic cerebral angiography considerably can be very low.

Natural history of cerebral dot-like cavernomas.

AIM: To elucidate the natural history of dot-like or "black spot" cavernomas. MATERIALS AND METHODS: Data of 18 children with black spot cavernomas were analysed retrospectively. RESULTS: Eleven boys and seven girls presented 187 black spot cavernomas during a mean observation period of 5.5 years. Mean and median age at diagnosis of the 187 cavernomas was 9.6 years. There were 70 de novo black spot cavernomas. Boys presented significantly more cavernomas than girls. There were three KRIT1 mutation carriers and four PDCD 10 mutation carriers. Children with a PDCD 10 mutation presented significantly more lesions than those children with a KRIT1 mutation (mean number of lesions per patient: 23.3 versus 3.3, respectively). There were 10 radiological haemorrhagic events caused by 10 black spot lesions. Two of these events were symptomatic. The haemorrhage rate of black spot cavernomas was 0.7% per lesion-year. CONCLUSIONS: A mean bleeding rate of 0.7% per lesion-year is lower than the overall haemorrhage rates provided in the literature. Nonetheless, black spot cavernomas are not purely benign lesions. Furthermore, genetic mutations may play a role in the natural history of black spot cavernomas.

Results of Temporary Stent-assisted Coil Embolization (CATS) for the Treatment of Wide-neck Aneurysms : A 10-year Single Center Experience.

PURPOSE: In intracranial wide-neck aneurysms, simple coil embolization is often not a feasible treatment option. Balloon-assisted coiling comes with the drawback of blood flow impairment, whereas permanent stent placement requires long-term antiplatelet therapy. Temporary stent-assisted coiling (coiling assisted by temporary stenting, CATS) is an alternative that eliminates both disadvantages. Because prior studies included only small numbers of patients, it was our aim to analyze the safety and effectiveness of this technique in a larger cohort of patients. METHODS: We retrospectively evaluated all endovascular aneurysm treatments at our institution from 2011 to 2020. Out of a total of 688 aneurysm treatments, we intended to perform 95 (14%) with temporary stent-assisted coiling and included them in our study. RESULTS: Sixty-four (64)% of aneurysms were acutely ruptured, 3% were symptomatic but unruptured, and 33% were incidental. Successful stent recovery was possible in 93% of treatments. Initial complete and adequate occlusion rate were 53% and 82%, respectively. Long-term follow-up at 6 and 12 months was available for 71% and 44% of cases. Aneurysm recurrence was observed in 10% of cases after 6 months, and in 17% after 1 year or later. Periprocedural complications were noted in 12 cases (13%), of which only 1 complication was definitely associated with temporary stent-assisted coiling (1%). One of the periprocedural complications resulted in neurological damage, the other complications were asymptomatic. CONCLUSION: Temporary stent-assisted coiling appears to be a safe and effective treatment method in intracranial wide-neck aneurysms. Procedural safety appears to be comparable with balloon remodeling or permanent stent-assisted coiling, but it comes with the further benefit of diminished need for posttreatment antiplatelet therapy, which may improve the outcome of patients. However, to define the true value and potential benefit of this technique, further prospective studies are required.

Investigation of Cerebral Hemodynamics During Endovascular Aspiration: Development of an Experimental and Numerical Setup.

PURPOSE: Acute ischemic stroke is a life-threatening emergency caused by an occlusion of a cerebral artery through a blood clot. Aspiration thrombectomy is an endovascular therapy for the removal of vessel occlusions. However, open questions regarding the hemodynamics during the intervention remain, motivating investigations of blood flow within cerebral arteries. In this study, we present a combined experimental and numerical approach to analyze hemodynamics during endovascular aspiration. METHODS: We have developed an in vitro setup for investigations of hemodynamic changes during endovascular aspiration within a compliant model of patient-specific cerebral arteries. Pressures, flows, and locally resolved velocities were obtained. In addition, we established a computational fluid dynamics (CFD) model and compared the simulations during physiological conditions and in two aspiration scenarios with different occlusions. RESULTS: Flow redistribution within cerebral arteries after ischemic stroke is strongly dependent on the severity of the occlusion and on the volume flow extracted by endovascular aspiration. Numerical simulations exhibit an excellent correlation of R = 0.92 for flow rates and a good correlation of R = 0.73 for pressures. Further on, the local velocity field inside the basilar artery had a good agreement between CFD model and particle image velocimetry (PIV) data. CONCLUSION: The presented setup allows for in vitro investigations of artery occlusions and endovascular aspiration techniques on arbitrary patient-specific cerebrovascular anatomies. The in silico model provides consistent predictions of flows and pressures in several aspiration scenarios.

Causes of Death in Endovascularly Treated Patients with Acute Stroke.

BACKGROUND AND PURPOSE: Because stroke therapy has changed with the introduction of endovascular stroke treatment as a standard approach, studies on intrahospital causes of death from stroke are no longer up-to-date. The purpose of this observational study was to present the causes of death during hospitalization of patients with ischemic stroke who received endovascular stroke treatment, with the focus on a differentiation of curative and secondary palliative treatment. MATERIALS AND METHODS: We studied a total cohort of 1342 patients who received endovascular stroke treatment in a tertiary stroke center (Aachen, Germany) between 2010 and 2020 and analyzed the causes of death in all 326 consecutive deceased patients. We distinguished between curative treatment and a secondary palliative approach and analyzed causes of death and treatment numbers across the years. RESULTS: In the entire cohort of 326 deceased patients, the most common cause of death was of a cerebrovascular nature (51.5%), followed by pneumonia and sepsis (25.8%) and cardiovascular causes (8.3%). Neurovascular causes constituted 75.8% of reasons for palliation. In the group with a secondary palliative approach, causes of death were neurovascular in 54.0% of patients and pneumonia and sepsis in 26.0% of patients. CONCLUSIONS: Cerebrovascular causes in patients with stroke play a major role in the intrahospital causes of death and reasons for palliation. Considering the large proportion of secondarily palliative-treated patients, reasons for palliation should be considered instead of causes of death to avoid concealment by, for example, life-terminating measures.

Diagnostic Performance of Whole-Body Ultra-Low-Dose CT for Detection of Mechanical Ventriculoperitoneal Shunt Complications: A Retrospective Analysis.

BACKGROUND AND PURPOSE: Radiographic shunt series are still the imaging technique of choice for radiologic evaluation of VP-shunt complications. Radiographic shunt series are associated with high radiation exposure and have a low diagnostic performance. Our aim was to investigate the diagnostic performance of whole-body ultra-low-dose CT for detecting mechanical ventriculoperitoneal shunt complications. MATERIALS AND METHODS: This retrospective study included 186 patients (mean age, 54.8 years) who underwent whole-body ultra-low-dose CT (100 kV[peak]; reference, 10 mAs). Two radiologists reviewed the images for the presence of ventriculoperitoneal shunt complications, image quality, and diagnostic confidence. On a 5-point Likert scale, readers scored image quality and diagnostic confidence (1 = very low, 5 = very high). Sensitivity, specificity, positive predictive value, and negative predictive value were calculated. Radiation dose estimation of whole-body ultra-low-dose CT was calculated and compared with the radiation dose of a radiographic shunt series. RESULTS: 34 patients positive for VP-shunt complications were correctly identified on whole-body ultra-low-dose CT by both readers. No false-positive or -negative cases were recorded by any of the readers, yielding a sensitivity of 100% (95% CI, 87.3%-100%), a specificity of 100% (95% CI, 96.9%-100%), and perfect agreement (κ = 1). Positive and negative predictive values were high at 100%. Shunt-specific image quality and diagnostic confidence were very high (median score, 5; range, 5-5). Interobserver agreement was substantial for image quality (κ = 0.73) and diagnostic confidence (κ = 0.78). The mean radiation dose of whole-body ultra-low-dose CT was significantly lower than the radiation dose of a conventional radiographic shunt series (0.67 [SD, 0.4] mSv versus 1.57 [SD, 0.6] mSv; 95% CI, 0.79-1.0 mSv; P < .001). CONCLUSIONS: Whole-body ultra-low-dose CT allows detection of ventriculoperitoneal shunt complications with excellent diagnostic accuracy and diagnostic confidence. With concomitant radiation dose reduction on contemporary CT scanners, whole-body ultra-low-dose CT should be considered an alternative to the radiographic shunt series.

Model-free fMRI group analysis using FENICA.

Exploratory analysis of functional MRI data allows activation to be detected even if the time course differs from that which is expected. Independent Component Analysis (ICA) has emerged as a powerful approach, but current extensions to the analysis of group studies suffer from a number of drawbacks: they can be computationally demanding, results are dominated by technical and motion artefacts, and some methods require that time courses be the same for all subjects or that templates be defined to identify common components. We have developed a group ICA (gICA) method which is based on single-subject ICA decompositions and the assumption that the spatial distribution of signal changes in components which reflect activation is similar between subjects. This approach, which we have called Fully Exploratory Network Independent Component Analysis (FENICA), identifies group activation in two stages. ICA is performed on the single-subject level, then consistent components are identified via spatial correlation. Group activation maps are generated in a second-level GLM analysis. FENICA is applied to data from three studies employing a wide range of stimulus and presentation designs. These are an event-related motor task, a block-design cognition task and an event-related chemosensory experiment. In all cases, the group maps identified by FENICA as being the most consistent over subjects correspond to task activation. There is good agreement between FENICA results and regions identified in prior GLM-based studies. In the chemosensory task, additional regions are identified by FENICA and temporal concatenation ICA that we show is related to the stimulus, but exhibit a delayed response. FENICA is a fully exploratory method that allows activation to be identified without assumptions about temporal evolution, and isolates activation from other sources of signal fluctuation in fMRI. It has the advantage over other gICA methods that it is computationally undemanding, spotlights components relating to activation rather than artefacts, allows the use of familiar statistical thresholding through deployment of a higher level GLM analysis and can be applied to studies where the paradigm is different for all subjects.

Correlation analyses of detection thresholds of four different odorants.

The detection threshold task of the Sniffin` Sticks can be conducted using two different odorants - n-butanol or phenylethyl alcohol (PEA). Previous studies show contradictory results regarding the correlation analysis of the two odorants. The current study investigated the relationship between PEA and n-butanol with respect to previous findings and subject population. We compared four different odorants (PEA, n-butanol, isoamyl butyrate, isobutanol) in an olfactory detection threshold task depending on subject population. Test odorants were applied to 73 healthy subjects. The experiment was divided into two sessions performed on two different days. The correlation coefficient between individual thresholds of PEA and n-butanol was not significant when exclusively normosmic subjects were included, but significant when additionally hyposmic, older subjects were studied. Comparable results were found for the analysis of the odorants n-butanol and isoamyl butyrate. Correlation between n-butanol and isobutanol was significant, both for exclusively normosmic, and additionally older, hyposmic subjects. The analyses of all other odorants revealed no significant correlations. Results give explanations for previous contradictory findings regarding investigations of PEA and n-butanol in a detection threshold task, and indicate that a formal validation of the Sniffin` Sticks with PEA as odorant is required.

[Bilateral wrist drop - central or peripheral lesion?]. / Bilaterale Fallhand - Zentrale oder Periphere Läsion?

The wrist drop, also called carpoptosis or drop hand, is a common clinical presentation in case of peripheral damage to the radial nerve. But what about the picture of a bilateral finger/wrist drop?! We report the case of a 61-year-old female patient who was admitted to the hospital for myocardial infarction. Subsequently she developed a right dominant bilateral wrist drop. Further neurological examination revealed a positive Wartenberg sign pointing towards a central motoric dysfunction. The following native cerebral CT scan demonstrated bilateral hypodense lesions in both hand knobs in the precentral gyri. Subsequent MRI confirmed acute cerebral infarction in these two but also several other, clinically silent, locations. Further diagnostic work-up revealed a hypokinetic cardiac apex suggesting cardiac embolism to be the cause for cerebral thrombembolism and the clinically leading symptom of right-dominant bilateral finger/wrist drop. Besides the case presentation also the differential diagnosis and clinical test for diagnostic work-up of wrist drops are presented and discussed.

Chemosensory properties of human sweat.

Human sweat contains a mixture of odorants with trigeminal as well as olfactory properties. It has been shown that trigeminal perception is necessary to localize odors and that humans are not able to localize substances that only activate the olfactory system. To analyze the chemosensory properties of human sweat, we studied humans' ability to localize sweat stimuli to the different nostrils. Human sweat was collected during a bicycle workout (20 males) and was then applied to 34 different subjects (17 females) during odor detection and localization experiments by using an olfactometer. During the detection experiment, subjects were instructed to discriminate between sweat stimuli (20) and blanks (10). During the localization experiment, they were assigned to allocate the stimuli to either the right (15) or the left nostril (15). We found that subjects were able to detect the sweat stimuli with moderate to high sensitivity. However, they failed to localize the sweat stimuli to the accurate nostril above chance level. Due to this inability to localize the stimuli, we conclude that human sweat does not activate the intranasal trigeminal system but only the olfactory system.

Outcome prediction in traumatic brain injury: comparison of neurological status, CT findings, and blood levels of S100B and GFAP.

OBJECTIVE: To investigate the predictive value of early serum levels of S100B and glial fibrillary acidic protein (GFAP) in traumatic brain injury. METHODS: Sixty patients admitted within 24 h of trauma were included. Neurological status on admission (Glasgow Coma Scale), initial cranial computed tomography (CCT) studies (Marshall Computed Tomographic Classification), and outcome after 6 months (Glasgow Outcome Scale) were evaluated. S100B and GFAP levels were determined on admission and 24 h after trauma. RESULTS: Blood levels of S100B and GFAP were elevated following head trauma and quantitatively reflected the severity of trauma. S100B levels after 24 h and on admission were of higher predictive value than CCT findings or clinical examination. GFAP, but not S100B levels rapidly declined after trauma. CONCLUSIONS: Blood levels of S100B and GFAP indicate the severity of brain damage and are correlated with neurological prognosis after trauma. Both methods can yield additional prognostic information if combined with clinical and CCT findings.

Comparison of two different odorants in an olfactory detection threshold test of the Sniffin’ Sticks.

The olfactory test battery Sniffin' Sticks is a test of nasal chemosensory function that is based on pen-like devices for odour presentation. It consists of three olfactory subtests: threshold, discrimination, and identification. The detection threshold can be measured using two different odorants--n-butanol or PEA (phenylethyl alcohol). Both tasks are commonly applied in published studies, but little is known about the formal comparison of values obtained using them. Unlike the Sniffin' Sticks with n-butanol as odorant, there is poor validation for the threshold subtest with the odorant PEA. The purpose of this study was to compare these two different odorants. Both odorants were applied to 100 normosmic, healthy subjects (50 females). The experiment was divided into two sessions performed on two different days. After each threshold test the discrimination and identification subtests were conducted. We obtained significant differences in detection thresholds of PEA and n-butanol. The mean score of PEA threshold and PEA TDI (sum of threshold, discrimination, identification) was significantly higher compared to n-butanol. No significant correlation between individual PEA and n-butanol thresholds was observed. The differences between both odorants indicate that a formal validation of the Sniffin' Sticks with PEA as odorant for probing olfactory thresholds may be required.

Investigation of breathing parameters during odor perception and olfactory imagery.

Compared with visual and auditory imagery, little is known about olfactory imagery. There is evidence that respiration may be altered by both olfactory perception and olfactory imagery. In order to investigate this relationship, breathing parameters (respiratory minute volume, respiratory amplitude, and breathing rate) in human subjects during olfactory perception and olfactory imagery were investigated. Fifty-six subjects having normal olfactory function were tested. Nasal respiration was measured using a respiratory pressure sensor. Using an experimental block design, we alternately presented odors or asked the subjects to imagine a given smell. Four different pleasant odors were used: banana, rose, coffee, and lemon odor. We detected a significant increase in respiratory minute volume between olfactory perception and the baseline condition as well as between olfactory imagery and baseline condition. Additionally we found significant differences in the respiratory amplitude between imagery and baseline condition and between odor and imagery condition. Differences in the breathing rate between olfactory perception, olfactory imagery, and baseline were not statistically significant. We conclude from our results that olfactory perception and olfactory imagery both have effects on the human respiratory profile and that these effects are based on a common underlying mechanism.