The Impact of Acoustic fMRI-Noise on Olfactory Sensitivity and Perception.

Sensory perception is neither static nor simple. The senses influence each other during multisensory stimulation and can be both suppressive and super-additive. As most knowledge of human olfactory perception is derived from functional neuroimaging studies, in particular fMRI, our current understanding of olfactory perception has systematically been investigated in an environment with concurrent loud sounds. To date, the confounding effects of acoustic fMRI-noise during scanning on olfactory perception have not yet been investigated. In this study we investigate how acoustic noise derived from the rapid switching of MR gradient coils, affects olfactory perception. For this, 50 subjects were tested in both a silent setting and an fMRI-noise setting, in a randomised order. We found that fMRI-related acoustic noise had a significant negative effect on the olfactory detection threshold score. No significant effects were identified on olfactory discrimination, identification, identification certainty, hedonic rating, or intensity rating.

Pepper with and without a sting: Brain processing of intranasal trigeminal and olfactory stimuli from the same source.

Humans have distinct and overlapping brain regions for the processing of intranasal olfactory or trigeminal stimuli. It may be assumed that trigeminal stimulants and "trigeminal-free" odorous stimuli from the same source are processed differently in the human brain. Using functional magnetic resonance imaging (fMRI), this study investigated the question whether the black pepper (Piper nigrum) derived trigeminal active compound piperine and the trigeminal-free pepper essential oil (pepperEO) are processed in relation to their degree of trigeminal stimulation. Twenty-one young healthy adults underwent a fMRI scan where piperine and pepperEO were delivered orthonasally using an olfactometer. Ratings for intensity, irritability, and pleasantness of each stimulus were obtained at the end of the scanning session. Results showed brain activation of the trigeminal network in response to piperine, and olfactory-related areas in response to pepperEO. PepperEO induced larger activations in the trigeminal network as compared to piperine. This was possibly due to the associative learning for the pungent sensations of pepperEO. In addition, conjunction analyses showed that the secondary somatosensory area, insula, and thalamus were involved in the processing of both piperine and pepperEO. In conclusion, the results strongly suggest that the cerebral representations of trigeminal irritants can be evoked by learned associations.

Androstenol--a steroid derived odor activates the hypothalamus in women.

BACKGROUND: Whether pheromone signaling exists in humans is still a matter of intense discussion. In the present study we tested if smelling of Androstenol, a steroid produced by the human body and reported to affect human behavior, may elicit cerebral activation. A further issue was to evaluate whether the pattern of activation resembles the pattern of common odors. METHODOLOGY: PET measurements of regional cerebral blood flow (rCBF) were conducted in 16 healthy heterosexual women during passive smelling of Androstenol, four ordinary odors (OO), and odorless air (the base line condition). PRINCIPAL FINDINGS: Smelling Androstenol caused activation of a portion of the hypothalamus, which according to animal data mediates the pheromone triggered mating behavior. Smelling of OO, on the other hand, engaged only the classical olfactory regions (the piriform cortex, lateral amygdala, anterior insular and anterior cingulate cortex). CONCLUSIONS: The observed pattern of activation is very similar to the pattern previously detected with 4,16-androstadien-3-one in heterosexual females. It suggests that several compounds released by human body may activate cerebral networks involved in human reproduction.

Pheromone signal transduction in humans: what can be learned from olfactory loss.

Because humans seem to lack neuronal elements in the vomeronasal organ (VNO), many scientists believe that humans are unable to detect pheromones. This view is challenged by the observations that pheromone-like compounds, 4,16-androstadien-3-one (AND) and oestra-1,3,5(10),16-tetraen-3-ol (EST), activate the human hypothalamus. Whether these activations are mediated via VNO, venous blood or olfactory mucosa is presently unknown. To disentangle between the three alternatives, we conducted activation studies in 12 heterosexual males with chronic anosmia because of nasal polyps. Polyposis hampers signal transduction via the olfactory mucosa without interfering with the VNO or the pheromone transport via venous blood. Twelve healthy men served as controls. Subjects were investigated with (15)O-H(2)O PET during smelling of odorless air (base line), AND, EST, vanillin, and acetone. Smelling of EST activated the anterior hypothalamus in controls, but not anosmics. Neither did the anosmics display cerebral activations with AND or vanillin. Clusters were detected only with the trigeminal odorant acetone, and only in the thalamus, brainstem, the anterior cingulate, and parts of the sensorimotor cortex. Direct comparisons with controls (controls-anosmics) showed clusters in the olfactory cortex (amygdala and piriform cortex) with AND, vanillin, and acetone, and in the anterior hypothalamus with EST. The observed absence of olfactory and presence of trigeminal activations in anosmics indicates that polyposis primarily affected signal processing via the olfactory mucosa. The anosmics inability to activate the hypothalamus with EST, therefore, suggests that in healthy men EST signals were primarily transmitted via the olfactory system.

Functional mapping of human brain in olfactory processing: a PET study.

This study describes the functional anatomy of olfactory and visual naming and matching in humans, using positron emission tomography (PET). One baseline control task without olfactory or visual stimulation, one control task with simple olfactory and visual stimulation without cognition, one set of olfactory and visual naming tasks, and one set of olfactory and visual matching tasks were administered to eight normal volunteers. In the olfactory naming task (ON), odors from familiar items, associated with some verbal label, were to be named. Hence, it required long-term olfactory memory retrieval for stimulus recognition. The olfactory matching task (OM) involved differentiating a recently encoded unfamiliar odor from a sequentially presented group of unfamiliar odors. This required short-term olfactory memory retrieval for stimulus differentiation. The simple olfactory and visual stimulation resulted in activation of the left orbitofrontal region, the right piriform cortex, and the bilateral occipital cortex. During olfactory naming, activation was detected in the left cuneus, the right anterior cingulate gyrus, the left insula, and the cerebellum bilaterally. It appears that the effort to identify the origin of an odor involved semantic analysis and some degree of mental imagery. During olfactory matching, activation was observed in the left cuneus and the cerebellum bilaterally. This identified the brain areas activated during differentiation of one unlabeled odor from the others. In cross-task analysis, the region found to be specific for olfactory naming was the left cuneus. Our results show definite recruitment of the visual cortex in ON and OM tasks, most likely related to imagery component of these tasks. The cerebellar role in cognitive tasks has been recognized, but this is the first PET study that suggests that the human cerebellum may have a role in cognitive olfactory processing as well.

Neural mechanisms involved in odor pleasantness and intensity judgments.

Olfactory processing in the human brain was examined using positron emission tomography. Twelve normal volunteers were scanned while smelling pairs of odors: they were asked to judge which odor was more pleasant in one condition, and which was more intense in a second condition; they also were scanned while sniffing an odorless stimulus. As in prior studies, greater cerebral blood flow was found in the right orbitofrontal cortex during both pleasantness and intensity judgments as compared to baseline. Cerebellar activity was also seen, but contrary to expectations no activity was detected in the primary olfactory (piriform) cortex. Only the pleasantness judgment elicited additional activity within the hypothalamus, suggesting that this structure may be involved in affective processing that requires access to information about internal state.