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.

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.

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.

Potential impact of a 32-channel receiving head coil technology on the results of a functional MRI paradigm.

PURPOSE: The authors investigated the potential of a 32-channel (32ch) receiving head coil for functional magnetic resonance imaging (fMRI) compared to a standard eight-channel (8ch) coil using a motor task. MATERIAL AND METHODS: Brain activation was analyzed in 14 healthy right-handed subjects performing finger tapping with the right index finger (block design) during two experimental sessions, one with the 8ch and one with the 32ch coil (applied in a pseudorandomized order). Additionally, a phantom study was performed to compare signal-to-noise ratios (SNRs) of both coils. RESULTS: During both fMRI sessions, analysis of motor conditions resulted in an activation of the left "hand knob" (precentral gyrus). Application of the 32ch coil obtained additional activation clusters in the right cerebellum, left superior frontal gyrus (SMA), left supramarginal gyrus, and left postcentral gyrus. The phantom study revealed a significantly higher SNR for the 32ch coil compared to the 8ch coil in superficial cortical areas located near the surface of the brain. CONCLUSION: The 32ch technology has a potential impact on fMRI studies, especially in paradigms that result in activation of cortical areas located near the surface of the brain.

Trigeminal perception is necessary to localize odors.

The human ability to localize odorants has been examined in a number of studies, but the findings are contradictory. In the present study we investigated the human sensitivity and ability to localize hydrogen sulphide (H(2)S), which in low concentrations stimulates the olfactory system selectively, the olfactory-trigeminal substance isoamyl acetate (IAA), and the trigeminal substance carbon dioxide (CO(2)). A general requirement for testing of localization was the conscious perception of the applied stimuli by the participants. Using Signal Detection Theory, we determined the human sensitivity in response to stimulation with these substances. Then the subjects' ability to localize the three different substances was tested. We found that humans can detect H(2)S in low concentration (2 ppm) with moderate sensitivity, and possess a high sensitivity in response to stimulation with 8 ppm H(2)S, 17.5% IAA, 50% v/v CO(2). In the localization experiment, subjects could localize neither the low nor the high concentration of H(2)S. In contrast, subjects possessed the ability to localize IAA and CO(2) stimuli. These results clearly demonstrate that humans, in spite of the aware perception, are not able to localize substances which only activate the olfactory system independent of their concentration, but they possess an ability to localize odorants that additionally excite the trigeminal system.