ofMRI

ofMRI, short for olfactory functional magnetic resonance imaging, is a specialized use of functional MRI that investigates the neural processing of smell. By presenting odor stimuli while measuring blood-oxygenation level-dependent signals, ofMRI maps brain activity associated with odor detection, discrimination, and evaluation. The olfactory system involves pathways from the olfactory bulb to primary and secondary cortices, including the piriform cortex, orbitofrontal cortex, amygdala, insula, and hippocampus.

Methods: Odor delivery is achieved with computer-controlled olfactometers that synchronize stimulus onset with MRI triggers. Designs commonly employ block or event-related paradigms. Imaging typically uses BOLD fMRI at 3 Tesla, with higher-field studies at 7 Tesla offering improved spatial resolution but greater susceptibility to artifacts. Researchers face challenges maintaining stable odor concentration and controlling sniffing, which can introduce motion and global signal changes.

Data analysis focuses on preprocessing, motion and physiological noise correction, and region-of-interest or whole-brain analyses. Odor identity, intensity, valence, and pleasantness can differentially engage neural circuits, with primary responses in olfactory cortex and higher-order areas such as the orbitofrontal cortex encoding odor quality, reward value, and memory associations.

Applications: ofMRI is used to study normal olfactory perception and to investigate olfactory dysfunction in conditions such as anosmia, Parkinson's disease, and Alzheimer's disease. It can contribute to understanding odor memory, flavor perception, and affective processing of smells.

Limitations: The olfactory bulb and orbitofrontal cortex are near air-tissue interfaces, making signals prone to susceptibility and physiological noise. Odor delivery variability and sniffing behavior complicate cross-subject comparisons, and results require careful interpretation in the context of task design and any use of anesthesia or sedation.