Tractography indicates lateralized differences between trigeminal and olfactory pathways.

Area of Science:

• Neuroscience
• Sensory Perception
• Neuroimaging

Background:

• Odorous sensations involve both olfactory and trigeminal nerve pathways.
• The piriform cortex and orbitofrontal cortex (OFC) are key olfactory processing centers.
• The thalamus acts as a relay for sensory information, but its direct role in odor perception is less understood.

Purpose of the Study:

• To quantify white matter tracts connecting the piriform cortex to the OFC and thalamus using diffusion MRI.
• To investigate correlations between these neural pathways and subjective trigeminal and olfactory sensory perceptions.

Main Methods:

• Diffusion MRI was performed on 38 healthy subjects.
• Regions of interest were defined in the piriform cortex, OFC, and thalamus.
• Tractography was used to measure the number of streamlines (representing white matter connections) between these regions.

Main Results:

• A higher number of streamlines were found between the piriform cortex and thalamus in the left hemisphere.
• Conversely, more streamlines were observed between the piriform cortex and OFC in the right hemisphere.
• Streamlines connecting the piriform cortex and thalamus positively correlated with trigeminal odor intensity.
• Streamlines between the piriform cortex and OFC correlated with trigeminal odor detection thresholds.

Conclusions:

• Different chemosensory stimuli, including olfactory and trigeminal inputs, are processed via distinct neural networks.
• The thalamus and OFC play differential roles in processing odor intensity and detection thresholds, respectively.
• This study provides novel insights into the structural connectivity underlying chemosensory perception.