Abstract
PurposeThe diagnosis of olfactory dysfunction is mainly based on psychophysical measurements. The aim of the current study was to investigate how well the olfactory functional magnetic resonance imaging (fMRI) can effectively distinguish between normosmic people and subjects with olfactory dysfunction.MethodsThirty-eight participants were recruited for the study. Group 1 consisted of 22 subjects with olfactory dysfunction (mean age = 44.3 years, SD = 18.6), and Group two consisted of 16 participants with normal olfactory function (mean age = 49.6 years, SD = 11.6). Olfactory functions were assessed in great detail for all participants, and brain activation in response to odorous stimulation was assessed using fMRI.ResultsThe between-group comparison showed stronger odor induced brain activation of the primary olfactory area and the insular cortex among the normosmic group as compared to the dysosmic group. As indicated by the individual analysis, positive responses in the primary olfactory cortex were significantly higher in normosmic people (94%) than in subjects with olfactory dysfunction (41%). However, there was no association between individual fMRI parameters (including the percentage of BOLD signal change, activated cluster size and peak z value), and psychophysical olfactory test scores. Receiver operating characteristic analysis suggested the subjects could not be differentiated from normosmics based on their BOLD signal from the primary olfactory area, orbitofrontal cortex, or the insular cortex.ConclusionThere are large inter-individual variabilities for odor-induced brain activation among normosmic subjects and subjects with olfactory dysfunction, due to this variation, at present it appears problematic to diagnose olfactory dysfunction on an individual level using fMRI.
Highlights
Olfactory disorders are common with about one-fifth of the general population exhibiting decreased olfactory acuity and approximately 5% showing anosmia [1]
Previous studies have confirmed on a group level that subjects with olfactory dysfunction had reduced brain activation to odor stimuli in primary olfactory areas (POC), orbitofrontal cortex (OFC), and insular cortex compared to normosmic groups with normal olfaction [10,11,12]
Brain activations to odor stimulation in the normosmic group were shown in Fig. 3a, the local maxima of the main activated areas were found in the left POC (Montreal Neurological Institute [MNI] peak coordinates −26, −2, −18), insula (MNI peak coordinates −38, −8, 6 and 36, 0, 16), no obvious activations were found in the OFC (Fig. 3a)
Summary
Olfactory disorders are common with about one-fifth of the general population exhibiting decreased olfactory acuity and approximately 5% showing anosmia [1]. Odor information is first processed in the primary olfactory areas (POC) including the piriform cortex, entorhinal cortex and amygdala. Previous studies have confirmed on a group level that subjects with olfactory dysfunction had reduced brain activation to odor stimuli in POC, OFC, and insular cortex compared to normosmic groups with normal olfaction [10,11,12]. No research has been done to look into olfactory fMRI on an individual level among subjects with olfactory dysfunction. The present study set out to examine how well fMRI signals to odorous stimuli could discriminate between individuals with normal olfactory function and people with little or no olfactory function
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