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Objective: To investigate the differences in regions of brain activation in response to olfactory stimulation by functional magnetic resonance imaging in conditions of prior warning of an odor and without., Methods: Participants were 17 normal right-handed volunteers; 8 participants received prior warning of the odor (informed condition) and 9 participants were not pre-warned (naïve condition). The odorant used was isovaleric acid., Results: In the informed condition with prior warning, activation was observed in the putamen extending to the insula, amygdala, and inferior frontal gyrus, and there was instant reification of the odor, while in the naïve condition without prior warning, activation was observed in the anterior cingulate cortex, entorhinal cortex, putamen and inferior frontal gyrus, and recognition of the odor was difficult., Conclusions: These results suggest that the condition prior to olfactory stimulation, i.e., with or without prior warning, can affect recognition and regions of brain activation in response to olfactory stimulation using isovaleric acid. Differences in recognition and regions of brain activation between both conditions could be associated with response latencies, or degree of attention, expectation and/or concentration.

Objective: Olfactory dysfunction is common in patients with mild cognitive impairment (MCI) or Alzheimer's disease (AD). We sought to elucidate brain regions associated with olfactory dysfunction in patients with MCI and early AD by using 123I-IMP-SPECT to detect regional cerebral blood flow (CBF).Methods: We included 218 patients diagnosed with AD or MCI, who underwent a comprehensive battery of neuropsychiatric and neuropsychological tests, Alzheimer's Disease Assessment Scale-Cognitive Part (ADAS-Cog), and forward- and backward-digit span. Olfactory function was assessed using T&T olfactometry of five odors; patients stated whether they experienced any smell (detection test) and identified the odor (identification test). The association between single-photon emission computerized tomography based regional CBF and olfactory function was examined by voxel-by-voxel multiple regression analysis, considering sex, age, and education as covariate parameters.Results: Of the 218 patients, 78 had mildly impaired olfactory detection and 15 had olfactory detection loss; additionally, 213 had mild olfactory identification impairment. The odor detection score correlated significantly with the ADAS-Cog word recall score (r = 0.193, p = 0.004). The odor identification score correlated significantly with the ADAS memory (r = 0.408, p < 0.001) and ADAS orientation (r = 0.292, p < 0.001) scores. The odor identification score correlated negatively with CBF in the left temporal pole, entorhinal area, and bilateral frontal poles (p < 0.001).Conclusion: Olfactory identification dysfunction in patients with MCI and AD is attributable to reduced CBF of the left temporal pole, entorhinal area, and bilateral frontal pole. [ABSTRACT FROM AUTHOR]