Affiliations: [a] Departments of Radiology, Pennsylvania State University College of Medicine, Hershey, PA, USA
| [b] Departments of Neurology, Pennsylvania State University College of Medicine, Hershey, PA, USA
| [c] Departments of Neural & Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, PA, USA
| [d] Departments of Neurosurgery, Pennsylvania State University College of Medicine, Hershey, PA, USA
| [e] Unity Rehabilitation and Neurology at Ridgeway, Rochester, NY, USA
Correspondence:
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Correspondence to: Qing X. Yang, PhD, Department of Radiology, Pennsylvania State University College of Medicine, 500 University Drive, H066, Hershey, PA 17033, USA. Tel.: +1 717 531 6069; Fax: +1 717 531 8486; E-mail: qyang@hmc.psu.edu.
Note: [1] Present address: Department of Neurology, University ofCalifornia Los Angeles, Los Angeles, CA, USA
Abstract: Background: Olfactory deficits are present in early Alzheimer’s disease (AD) and mild cognitively impaired (MCI) patients. However, whether these deficits are due to dysfunction of the central or peripheral olfactory nervous system remains uncertain. This question is fundamentally important for developing imaging biomarkers for AD using olfactory testing. Objective: This study sought to use olfactory functional magnetic resonance imaging (fMRI) to further demonstrate the involvement of the central olfactory system in olfactory deficits in MCI and AD. Methods: We investigated the central olfactory system in 27 cognitively normal controls (CN), 21 MCI, and 15 AD subjects using olfactory fMRI with an odor-visual association paradigm during which a visual cue was paired with lavender odorant (odor condition) or odorless air (no-odor condition). Results: The CN subjects had significantly greater activated volume in the primary olfactory cortex during both the odor and no-odor conditions compared to either the MCI or AD groups (p < 0.05). No significant differences were observed between the odor and no-odor conditions within each group. No-odor condition activation in AD and MCI correlated with the cognitive and olfactory assessments. Conclusion: The no-odor condition, allowing investigation of activation patterns when the peripheral olfactory system was not directly involved, elicited the same functional response as the odor condition for each of the three groups. Thus, the olfactory activation deficits present in AD and MCI patients are most likely caused by degeneration of the central olfactory nervous system.
