Neuropsychiatric Disease and Treatment (Apr 2021)
Comparative Effects of Repetitive Odor Identification and Odor Memory Tasks on Olfactory Engagement in Older Populations – A Pilot fMRI Study
Abstract
Narayan Rai,1,* Maria Mananita Hipolito,1,* John W VanMeter,2 Riya Seth,3 Ayokunnumi Adenuga,3 Myeshia Shelby,4 Magdalena Misiak-Christian,5 Charles Nwaokobia,3 Kebreten F Manaye,5 Thomas O Obisesan,6 Evaristus Nwulia1,3 1Department of Psychiatry and Behavioral Sciences, Howard University, Washington DC, USA; 2Department of Neurology, Center for Functional and Molecular Imaging, Georgetown University Medical Center, Washington DC, USA; 3Evon Medics LLC, Elkridge, MD, USA; 4Howard University Graduate School, Washington DC, USA; 5Department of Physiology, Howard University, Washington DC, USA; 6Department of Medicine, Howard University, Washington DC, USA*These authors contributed equally to this workCorrespondence: Evaristus NwuliaDepartment of Psychiatry and Behavioral Sciences, Howard University, Washington DC, WA, USAEmail [email protected]: This study evaluated human Blood Oxygen Level-Dependent (BOLD) responses in primary and higher-order olfactory regions of older adults, using odor memory and odor identification tasks. The goal was to determine which olfactory and memory regions of interest are more strongly engaged in older populations comparing these two odor training tasks.Methods: Twelve adults 55– 75 years old (75% females) without intranasal or major neurological disorders performed repetitive odor memory and identification tasks using a 3-tesla magnetic resonance scanner. Odors were presented intermittently at 10-second bursts separated by 20-second intervals of odorless air. Paired t-tests were used to compare differences in the degree of activation between odor identification and odor memory tasks within individuals. An FDR cluster-level correction of p< 0.05 was used for multiplicity of tests (with a cluster-defining threshold set at p< 0.01 and 10 voxels).Results: Odor identification compared to memory (ie, odor identification > odor memory) contrasts had several areas of significant activation, including many of the classical olfactory brain regions as well as the hippocampus. The opposite contrast (odor memory > odor identification) included the piriform cortex, though this was not significant. Both tasks equally activated the piriform cortex, and thus when the two tasks are compared to each other this area of activation appears to be either absent (OI > OM) or only weakly observed (OM > OI).Conclusion: These findings from a predominantly African American sample suggest that odor identification tasks may be more potent than memory tasks in targeted olfactory engagement in older populations. Furthermore, repetitive odor identification significantly engaged the hippocampus – a region relevant to Alzheimer’s disease – more significantly than did the odor memory task. If validated in larger studies, this result could have important implications in the design of olfactory training paradigms.Keywords: blood oxygen level dependent responses, BOLD, odor memory, odor identification, olfactory engagement, olfactory training
