Olfactory system activation from sniffing: effects in piriform and orbitofrontal cortex.

Department of Neurology, Neuropsychology Section (RI 1773), Indiana University School of Medicine, Indianapolis, IN 46202, USA.
NeuroImage (Impact Factor: 6.13). 06/2004; 22(1):456-65. DOI: 10.1016/j.neuroimage.2004.01.008
Source: PubMed

ABSTRACT Neuroimaging studies suggest that piriform cortex is activated at least in part by sniffing. We used H(2)(15)O positron emission tomography (PET) to study 15 healthy volunteers while they participated in four conditions, two of which were sniffing odorants and odorless air. The remaining two conditions involved a constant, very low flow of either odorized or odorless air during velopharyngeal closure (VPC), a technique that prevents subject-induced airflow through the nasal passages. Contrary to expectation, sniffing under odorless conditions did not induce significant piriform and surrounding cortical (PC+) activity when compared to odorless VPC, even at a liberal statistical threshold. However, a small correlation emerged in PC+ between the difference signal of [odorless sniffing - odorless VPC] and peak rate of nasal pressure change. PC+ activity was, however, strongly evoked by odorant exposure during sniffing and VPC, with neither technique showing greater activation. Activity in orbitofrontal (olfactory association) cortex was absent during odorant stimulation (OS) with VPC, but present during odorant sniffing. Sniffing may therefore play an important role in facilitating the higher-order analysis of odors. A right orbitofrontal region was also activated with odorless sniffing, which suggests a possible orbitofrontal role in guided olfactory exploration.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An important challenge in olfaction research is to understand how percepts relate to the molecular structure of stimuli. Previous psychophysical studies showed that, whereas structurally simple odorant molecules evoked a more uniform qualitative perception as revealed by the use of a small number of labels to describe their olfactory quality, more complex odorants evoked a larger variety of olfactory qualities, reflecting a more heterogeneous qualitative perception. The present study examined how this influence of odorant molecular complexity on perception is reflected in the human brain. To this end, participants were stimulated with structurally simple and complex odorant molecules and their brain responses were assessed by fMRI. Low and high complexity odorants were judged to have the same intensity, pleasantness and familiarity (p>0.05 in all cases), whereas complex odorants induced more quality labels than simple odorants (p<0.02) as expected. Imaging analysis of complex vs. simple odorants revealed significant activation in dorsal anterior cingulate gyrus, but not in primary olfactory areas. Taken together, these findings suggest dissociated neural representations of uniform and heterogeneous olfactory perception, highlighting for the first time the impact of odorant complexity on activity of cingulate gyrus. Copyright © 2014. Published by Elsevier Ltd.
    Neuroscience 12/2014; · 3.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this article is to investigate the cortical metabolic arrangements in olfactory processing by using F fluorodeoxyglucose (FDG) positron emission tomography/computed tomography.Twenty-six normosmic individuals (14 women and 12 men; mean age 46.7 ± 10 years) were exposed to a neutral olfactory condition (NC) and, after 1 month, to a pure olfactory condition (OC) in a relatively ecological environment, that is, outside the scanner. All the subjects were injected with 185-210 megabecquerel of F FDG during both stimulations. Statistical parametric mapping version 2 was used in order to assess differences between NC and OC.As a result, we found a significant higher glucose consumption during OC in the cuneus, lingual, and parahippocampal gyri, mainly in the left hemisphere. During NC, our results show a relative higher glucose metabolism in the left superior, inferior, middle, medial frontal, and orbital gyri as well as in the anterior cingulate cortex.The present investigation, performed with a widely available functional imaging clinical tool, may help to better understand the neural responses associated to olfactory processing in healthy individuals and in patients with olfactory disorders by acquiring data in an ecologic, noise-free, and resting condition in which possible cerebral activations related to unwanted attentional processes might be avoided.
    Medicine. 10/2014; 93(19):e103.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The plasticity of brain function, especially reorganization after stroke or sensory loss, has been investigated extensively. Based upon its special characteristics, the olfactory system allows the investigation of functional networks in patients with smell loss, as it holds the unique ability to be activated by the sensorimotor act of sniffing, without the presentation of an odor. In the present study, subjects with chronic peripheral smell loss and healthy controls were investigated using functional magnetic resonance imaging (fMRI) to compare functional networks in one of the major olfactory areas before and after an olfactory training program. Data analysis revealed that olfactory training induced alterations in functional connectivity networks. Thus, olfactory training is capable of inducing neural reorganization processes. Furthermore, these findings provide evidence for the underlying neural mechanisms of olfactory training.
    Neural Plasticity 11/2014; · 2.86 Impact Factor

Full-text (2 Sources)

Available from
Jun 1, 2014