The neural cascade of olfactory processing: a combined fMRI-EEG study

Area of Science:

• Neuroscience
• Olfactory Neuroscience
• Cognitive Neuroscience

Background:

• Olfaction, the sense of smell, relies on respiration to deliver odorants to the nasal cavity.
• Previous research used electroencephalogram dipole modeling (EEG/DT) to identify an inspiration-triggered neural cascade in olfactory processing.
• This cascade progresses from limbic olfactory regions to frontal cortical areas.

Purpose of the Study:

• To replicate and extend previous findings on the olfactory neural cascade using both fMRI and EEG.
• To investigate the spatiotemporal dynamics of odor perception.
• To validate the spatial profile of the olfactory cascade identified by EEG source modeling.

Main Methods:

• Integration of functional magnetic resonance imaging (fMRI) for spatial resolution and electroencephalogram (EEG) for temporal resolution.
• Leveraging the time-locked relationship between inspiration and olfactory processing.
• EEG/DT was used to detect transient activity in primary olfactory regions.

Main Results:

• Both fMRI and EEG identified converging brain activation in the orbitofrontal cortex association regions.
• This activation occurred between approximately 150-300 ms after inspiration onset.
• EEG/DT detected earlier, transient activity in the parahippocampal gyrus and amygdala around 50 ms post-inspiration.

Conclusions:

• The study partially validates the spatial profile of the olfactory cascade previously identified by EEG source modeling.
• The findings highlight the complementary strengths of fMRI and EEG in studying olfactory processing.
• This research opens new avenues for investigating human olfaction.